Flaws and pitfalls in the chemical analysis of feathers: bad news-good news for avian chemoecology and toxicology

Influence of paternal factors on plastic ingestion and brominated chemical exposure in East Tropical Atlantic Procellariid chicks

The presence of plastic debris and organo-brominated compounds in the marine environment poses a concern to wildlife. Plastic can absorb and release chemical compounds, making their ingestion potentially harmful, while chemical compounds have become omnipresent, with a tendency to bioaccumulate in the food web. Seabirds are often used as indicators of marine plastic pollution, yet studies on the exposure of tropical communities to plastic contamination are still scarce. In this study we monitored the amounts of plastics in faeces and organo-brominated compounds ingested/assimilated in feathers by adults and chicks of Cape Verde shearwaters and Bulwer's petrels from Cabo Verde. Anthropogenic pollutants, polybrominated diphenyl ethers (PBDEs), and naturally generated methoxylated-PBDEs (MeO-PBDEs) were among the probed compounds. The frequency of plastic debris ingestion was similar in both species' adults and chicks, although, the characteristics of the ingested plastic differed. Frequency and number of microplastics increased throughout the nestling season for chicks from both species. All species and age groups showed the presence of PBDEs and MeO-PBDEs. Among PBDEs, Bulwer's petrels exhibited higher concentrations than Cape Verde shearwaters, and chicks had higher concentration profiles than adults. Specifically, Bulwer's petrel chicks showed higher concentrations than Cape Verde shearwater chicks. On the contrary, Cape Verde shearwater adults exhibited higher occurrence and concentrations of MeO-PBDEs when compared to Cape Verde shearwater chicks. We found no effect of plastic loadings or loadings of organohalogen contaminants on body condition or size, although harmful effects may be hidden or reveal themselves in a medium- to long-term. Feather samples from both adults and chicks were shown to be useful for comparing intraspecific contamination levels and appear suitable for the long-term assessment of organohalogen contaminants in seabirds. Species-specific foraging and feeding strategies are likely the drivers of the observed variation in organochlorine contamination burdens among seabird species.

Is minimally-invasive sampling the future of persistent organic pollutant (POP) research in birds? A meta-analysis on tissue comparisons

Persistent organic pollutants (POPs) bioaccumulate in the food chain and can cause ecotoxicity. In wild bird populations, various tissues are used to determine POP levels, including invasive (e.g., brain, fat, kidney, liver, muscle) and minimally-invasive tissues (e.g., blood, feather, preen oil). Minimally-invasive sampling, which does not require the death of the animal, opens new prospects for sampling birds as sentinels of environmental pollution and its consequences on fitness. However, POP variability between tissues is understudied, which is an essential prerequisite for making a reasoned choice about which tissues to sample. Here, we performed a meta-analysis of eight tissues across 115 studies comparing tissues across POP groups. We demonstrate increased use of minimally-invasive measures between 1974 and 2020. When grouping tissue correlations into three groups, "invasive:invasive", "invasive:minimally-invasive" and "minimally-invasive:minimally-invasive", we found that all three groups produced moderate to strong positive correlations with no difference seen between comparison groups. We demonstrate (1) lower POP concentrations in preen oil than fat, but no difference in detection frequencies, supporting preen oil use; (2) blood showed high concentration variability dependent on POP group but detection frequencies were comparable to liver and kidney; and (3) feathers demonstrated a significantly lower detection frequency than other matrices measured. By further researching minimally-invasive tissues, we increase our understanding of whether minimally-invasive tissues are ecologically representative of body-level toxicity. Our study supports blood and preen oil as substitutes for invasive measures when sampling living bird populations as they represent internal POP concentrations and provide significant benefits both practically and ethically.

Feather's Composition of South Polar Skua (Stercorarius maccormicki) Using WDXRF

This study investigated the feathers' composition of South polar skua (Stercorarius maccormicki) using WDXRF, evaluating the concentration of essential and non-essential elements in the feathers, and dividing it into rachis and barb parts. We collected South polar skuas feathers from Hennequin Point, King George Island, South Shetland, Antarctic Peninsula in January of 2013. Our results show that 18 elements were observed in the composition of the feathers, with a different concentration between the rachis and barbs, qualitatively and quantitatively. Only 3 elements observed were classified as non-essentials but still mostly elements do not have a function described in the literature to the feathers. According to our knowledge, this is the first study that uses this technique to evaluate the concentration of different elements in the feathers. The findings of this study highlight the use of alternative techniques to biomonitoring elements in the ecosystem and bring baseline information for future studies.

Mercury in Neotropical birds: a synthesis and prospectus on 13 years of exposure data

Environmental mercury (Hg) contamination of the global tropics outpaces our understanding of its consequences for biodiversity. Knowledge gaps of pollution exposure could obscure conservation threats in the Neotropics: a region that supports over half of the world's species, but faces ongoing land-use change and Hg emission via artisanal and small-scale gold mining (ASGM). Due to their global distribution and sensitivity to pollution, birds provide a valuable opportunity as bioindicators to assess how accelerating Hg emissions impact an ecosystem's ability to support biodiversity, and ultimately, global health. We present the largest database on Neotropical bird Hg concentrations (n = 2316) and establish exposure baselines for 322 bird species spanning nine countries across Central America, South America, and the West Indies. Patterns of avian Hg exposure in the Neotropics broadly align with those in temperate regions: consistent bioaccumulation across functional groups and high spatiotemporal variation. Bird species occupying higher trophic positions and aquatic habitats exhibited elevated Hg concentrations that have been previously associated with reductions in reproductive success. Notably, bird Hg concentrations were over four times higher at sites impacted by ASGM activities and differed by season for certain trophic niches. We developed this synthesis via a collaborative research network, the Tropical Research for Avian Conservation and Ecotoxicology (TRACE) Initiative, which exemplifies inclusive, equitable, and international data-sharing. While our findings signal an urgent need to assess sampling biases, mechanisms, and consequences of Hg exposure to tropical avian communities, the TRACE Initiative provides a meaningful framework to achieve such goals. Ultimately, our collective efforts support and inform local, scientific, and government entities, including Parties of the United Nations Minamata Convention on Mercury, as we continue working together to understand how Hg pollution impacts biodiversity conservation, ecosystem function, and public health in the tropics.

Mercury toxicity risk and corticosterone levels across the breeding range of the Yellow-breasted Chat

Mercury (Hg) is an environmental contaminant that can negatively impact human and wildlife health. For songbirds, Hg risk may be elevated near riparian habitats due to the transfer of methylmercury (MeHg) from aquatic to terrestrial food webs. We measured Hg levels in tail feathers sampled across the breeding range of the Yellow-breasted Chat (Icteria virens), a riparian songbird species of conservation concern. We assessed the risk of Hg toxicity based on published benchmarks. Simultaneously, we measured corticosterone, a hormone implicated in the stress response system, released via the hypothalamus-pituitary-adrenal axis. To better understand range-wide trends in Hg and corticosterone, we examined whether age, sex, subspecies, or range position were important predictors. Lastly, we examined whether Hg and corticosterone were correlated. Hg levels in chats were relatively low: 0.30 ± 0.02 µg/g dry weight. 148 out of 150 (98.6%) had Hg levels considered background, and 2 (1.6%) had levels considered low toxicity risk. Hg levels were similar between sexes and subspecies. Younger chats (<1 year) had higher Hg levels than older chats (>1 year). Hg levels were lowest in the northern and central portion of the eastern subspecies' range. Corticosterone concentrations in feathers averaged 3.68 ± 0.23 pg/mm. Corticosterone levels were similar between ages and sexes. Western chats had higher levels of corticosterone than eastern chats. Hg and corticosterone were not correlated, suggesting these low Hg burdens did not affect the activity of the hypothalamus-pituitary-adrenal axis. Altogether, the chat has low Hg toxicity risk across its breeding range, despite living in riparian habitats.

Spatial and dietary sources of elevated mercury exposure in white-tailed eagle nestlings in an Arctic freshwater environment

Human-induced mercury (Hg) contamination is of global concern and its effects on wildlife remain of high concern, especially in environmental hotspots such as inland aquatic ecosystems. Mercury biomagnifies through the food web resulting in high exposure in apex predators, such as the white-tailed eagle (Haliaeetus albicilla), making them excellent sentinel species for environmental Hg contamination. An expanding population of white-tailed eagles is inhabiting a sparsely populated inland area in Lapland, northern Finland, mainly around two large reservoirs flooded 50 years ago. As previous preliminary work revealed elevated Hg levels in this population, we measured Hg exposure along with dietary proxies (δ¹³C and δ¹⁵N) in body feathers collected from white-tailed eagle nestlings in this area between 2007 and 2018. Mercury concentrations were investigated in relation to territory characteristics, proximity to the reservoirs and dietary ecology as potential driving factors of Hg contamination. Mercury concentrations in the nestlings (4.97-31.02 μg g^-1 dw) were elevated, compared to earlier reported values in nestlings from the Finnish Baltic coast, and exceeded normal background levels (≤5.00 μg g^-1) while remaining below the tentative threshold of elevated risk for Hg exposure mediated health effect (>40.00 μg g^-1). The main drivers of Hg contamination were trophic position (proxied by δ¹⁵N), the dietary proportion of the predatory fish pike (Esox lucius), and the vicinity to the Porttipahta reservoir. We also identified a potential evolutionary trap, as increased intake of the preferred prey, pike, increases exposure. All in all, we present results for poorly understood freshwater lake environments and show that more efforts should be dedicated to further unravel potentially complex pathways of Hg exposure to wildlife.

Evaluation of homing pigeon feather tissue as a biomonitor of environmental metal concentrations in China

Biomonitoring provides direct evidence of the bioavailability and accumulation of toxic elements in the environment, and homing pigeons have been proposed as a biomonitor of atmospheric pollution. We evaluated metal concentrations in homing pigeon feather tissue as a biomonitoring tool. We measured cadmium, lead, and mercury concentrations in feathers collected from 5-6-yo homing pigeons from Guangzhou, Beijing, and Harbin, China during 2011, and feathers of 1, 5, and 10-yo homing pigeons collected from Guangzhou, Beijing, and Harbin, China during 2015-16. We compared metal concentrations in feathers between sexes and among ages and evaluated spatio-temporal differences. Correlations between feather metal concentrations and previously evaluated kidney and liver metal concentrations are reported. There were no significant differences in feather metal concentrations between male and female pigeons or among 1, 5, and 10-yo pigeons. Cadmium, lead, and mercury concentrations in feathers of 1-yo pigeons were significantly correlated with concentrations in liver and kidney tissues, although the correlations were not consistent. Spatio-temporal differences in feather metal concentrations suggest the usefulness of feathers in identifying areas of concern and remedial effectiveness. Homing pigeon feather metal concentrations appear to be useful as a screening biomonitoring tool.

Comparison of Two Different Feather Sampling Methods to Measure Corticosterone in Wild Greater Flamingos (Phoenicopterus roseus) and Wild Mallards (Anas platyrhynchos)

Simple Summary

The common standard sampling method to determine corticosterone in feathers (CORTf) is to pluck them from the bird’s skin. This procedure is considered to be painful, and the animals have to be caught and fixated firmly. Therefore, an animal experiment approval is required according to European and German legislation. In this study, we compared two methods: plucking vs. cutting feathers. The aim was to confirm the validation of an alternative less-invasive sampling technique. The specimens of this project were wild adult Mallards (Germany) and wild 1st-calender-year juvenile Greater Flamingos (Spain). In summary, there were no significant differences between the methods in terms of corticosterone results for both species. Additionally, no differences were found in CORTf between females and males of both species. In conclusion, these findings underline the suitability of cutting feathers as a sampling method for the determination of CORTf levels.

Abstract

This research project had the aim to validate the possible alternative and less-painful sampling method of cutting feathers close to the skin instead of plucking them for subsequent feather corticosterone analysis, confirming recently-published results for other species in captivity. Analyzing CORTf is often used in animal welfare studies in combination with behavioral monitoring. The background of this idea was to act in the sense of animal welfare and reduce the burden of animal studies according to the 3-R-Principle (Replacement, Reduction, and Refinement) by refining procedures. To confirm the hypothesis that the sampling method itself has no influence on CORTf levels measured, plucked and cut samples of the respective bird were collected. Birds of two wild species were used: the Mallard (Anas platyrhynchos) and the Greater Flamingo (Phoenicopterus roseus). The CORTf was measured by using an enzyme-linked immunosorbent assay (ELISA). The determined values were inspected for their mean values, standard deviation (SD), and average differences. Afterwards, the CORTf levels of both species were compared, according to the sampling method, with the concordance correlation coefficient (CCC). In the Bland-Altman (BA) plot the differences of the methods were displayed against the mean values. Additionally, sex, as a possible factor influencing CORTf, was analyzed using the Mann-Whitney U test. The values of CCC showed poor agreement in the comparability of the two methods, whereas the concordance of the BA plot was decent. The average differences between the methods were marginal for both species (Mallards: −0.16 pg/mm, Flamingos −0.13 pg/mm). In summary, all anomalies or differences between the methods were negligible. Therefore, the alternative sampling method seems to be as suitable as the common standard method. No significant difference was found between females and males. Nevertheless, our results suggest that CORTf should not be interpreted in just considering the values themselves, but the results they should be analyzed in the context of a wider set of parameters. Hence, further studies are encouraged to create a larger data pool.

Investigation of keratinase digestion to improve steroid hormone extraction from diverse keratinous tissues

Monitoring the physiology of wild populations presents many technical challenges. Blood samples, long the gold standard of wildlife endocrinology studies, cannot always be obtained. The validation and use of non-plasma samples to obtain hormone data have greatly improved access to more integrated information about an organism's physiological state. Keratinous tissues like skin, hair, nails, feathers, or baleen store steroid hormones in physiologically relevant concentrations, are stable across decades, and can be used to retrospectively infer physiological state at prior points in time. Most protocols for steroid extraction employ physical pulverization or cutting of the sample, followed by mixing with a solvent. Such methods do produce repeatable and useful data, but low hormone yield and detectability issues can complicate research on small or rare samples. We investigated the use of keratinase, an enzyme that breaks down keratin, to improve the extraction and yield of corticosterone from vertebrate keratin tissues. Corticosterone content of keratinase-digested extracts were compared to non-keratinase extracts for baleen from three species of whale (blue, Balaenoptera musculus; bowhead, Balaena mysticetus; southern right, SRW; Eubalaena australis), shed skin from two reptiles (tegu lizard, Salvator merianae; narrow-headed garter snake, Thamnophis rufipunctatus), hair from arctic ground squirrel (AGS; Urocitellus parryii), feathers from Purple Martins (PUMA; Progne subis), and spines from the short-beaked echidna (Tachyglossus aculeatus). We tested four starting masses (10, 25, 50, 100 mg) for each sample; digestion was most complete in the 10 and 25 mg samples. A corticosterone enzyme immunoassay (EIA) was validated for all keratinase-digested extracts. In all sample types except shed skin from reptiles, keratinase digestion improved hormone yield, with PUMA feathers and blue whale baleen having the greatest increase in apparent corticosterone content (100% and 66% more hormone, respectively). The reptilian shed skin samples did not benefit from keratinase digestion, actually yielding less hormone than controls. With further optimization and refinement, keratinase digestion could greatly improve yield of steroid hormones from various wildlife epidermal tissue types, allowing more efficient use of samples and ultimately improving understanding of the endocrine physiology of wild populations.

Research Note: A sip of stress. Effects of corticosterone supplementation in drinking water on feather corticosterone concentrations in layer pullets

The measurement of feather corticosterone concentrations (fCORT) is a comparatively new method for the evaluation of stress in wild and captive birds and may be a useful indicator in animal welfare research. The aim of this study was to assess the suitability of fCORT as an indicator of stress, and for this purpose a prolonged stress period was experimentally simulated by oral intake of corticosterone via drinking water and corticosterone concentrations were analyzed in feathers grown during this period. Layer pullets of both a control group (n = 20) and a CORT group (n = 20) were offered drinking water ad libitum throughout the entire experimental phase. The drinking water of the CORT group was supplemented with corticosterone at a concentration of 20 mg/l from the 64th to the 114th day of life. The vaned parts of the primaries 5 (P5s) were clipped on d 114 and fCORT was analyzed by ELISA after extraction. Body weights increased from day 64 until d 114 in both groups, however, at the end of the experiment, mean body mass in the CORT group was significantly lower than in the control group (P < 0.001). Pullets of the CORT group also showed shorter and lighter P5s as well as a retarded molt of the primaries. The supplementation of drinking water with corticosterone increased the average fCORT in the P5s of the CORT pullets compared with the control group (median: 110.3 pg/mm [interquartile range (IQR): 47.2] vs. 10.0 pg/mm [IQR: 2.5], P < 0.001). The results show that experimentally increased systemic corticosterone concentrations over a period of seven weeks in layer pullets are reflected in corticosterone concentrations of feathers grown during that time. This indicates that the measurement of fCORT may be a useful and minimally invasive tool for the evaluation of long-term stress in chicken and provides the basis for further investigations on its use in animal welfare research.

Trace elements fingerprint of feathers differs between breeding and non-breeding areas in an Afro-Palearctic migratory bird, the barn swallow (Hirundo rustica)

Trace elements are widespread contaminants that can potentially threaten ecosystems and human health. Considering their distribution and toxicity, monitoring their presence in animals represents a priority in environmental risk assessment. Migratory birds have been suggested to be useful biomonitors for trace elements because they can provide information on contaminants even from remote areas that they may exploit during their life cycle. The aim of this study was to analyse the contamination fingerprint of trace elements of African non-breeding staging grounds and European breeding areas in a long-distance migratory passerine bird, the barn swallow (Hirundo rustica). We collected feathers grown in the African non-breeding grounds and those grown in the breeding areas of Northern Italy and measured the levels of 12 trace elements (Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se and Zn) by DRC-ICP-MS. Multivariate analysis showed that elemental profiles of feathers grown in African non-breeding areas and in the Italian breeding ones clearly differed, with feathers grown in Africa showing higher concentrations of Al, Cu, Fe, Mn and Ni, but lower concentrations of As, Se and Zn, compared to those grown in Italy. In addition, levels of trace elements were age-dependent, with higher levels in older individuals than in younger ones. Our results add to the growing evidence that feathers of long-distance migratory birds are useful tools to monitor trace elements contamination profiles across continents.

Untangling causes of variation in mercury concentration between flight feathers

Bird feathers are one of the most widely used animal tissue in mercury biomonitoring, owing to the ease of collection and storage. They are also the principal excretory pathway of mercury in birds. However, limitations in our understanding of the physiology of mercury deposition in feathers has placed doubt on the interpretation of feather mercury concentratoins. Throughout the literature, moult sequence and the depletion of the body mercury pool have been taken to explain patterns such as the decrease in feather mercury from the innermost (P1) to the outermost primary feather (P10) of the wing. However, it has been suggested that this pattern is rather a measurement artefact as a result of the increased feather mass to length ratio along the primaries, resulting in a dilution effect in heavier feathers. Here, we attempt to untangle the causes of variation in feather mercury concentrations by quantifying the mercury concentration as μg of mercury (i) per gram of feather, (ii) per millimetre of feather, and (iii) per day of feather growth in the primary feathers of Bulwer's Petrel Bulweria bulwerii chicks, effectively controlling for some of the axes of variation that may be acting in adults, and monitoring the growth rate of primary feathers in chicks. The mercury concentration in Bulwer's Petrel chicks' primaries increased from the innermost to the outermost primary for all three concentration measures, following the order of feather emergence. These observations confirm that the pattern of mercury concentration across primary feathers is not an artefact of the measure of concentration, but is likely an effect of the order of feather growth, whereby the earlier grown feathers are exposed to higher blood mercury concentrations than are later moulted feathers as a result of blood mercury depletion.

Bird feathers are potential biomonitors for airborne elemental carbon

Birds can serve as effective biomonitors of air pollution, yet few studies have quantified external particulate matter accumulation on bird feathers. Biomonitoring of airborne elemental carbon (EC) is of critical significance because EC is a component of particulate matter with adverse effects on air quality and human health. To assess their effectiveness for use in EC monitoring, we compared EC accumulation on bird feathers at two sites that differed in vehicular traffic volume in an urban environment within the Dallas-Fort Worth Metropolitan Area, USA. Moulted flight feathers from domestic chickens were experimentally exposed to ambient EC pollution for 5 days in two urban microenvironments 1.5 km distant from each other that differed in traffic volume--adjacent to an interstate highway and a university campus bus stop. Feathers near the highway accumulated approximately eight times more EC (307 ± 34 μg m^-2 day^-1), on average, than feathers near the bus stop (40 ± 9 μg m^-2 day^-1). These findings indicate that EC accumulation on feathers varies over short distances within urban areas and that bird feathers potentially can be used for biomonitoring airborne EC.

Reconstructing avian mercury concentrations through time using museum specimens from New York State

We examined how variation in MeHg concentrations through time is reflected in birds, a taxon commonly used as a biological indicator of ecosystem health. Using museum specimens collected from 1880 to 2016, we measured feather MeHg concentrations in six species of birds that breed in New York State and have distinct dietary and habitat preferences. We predicted that MeHg concentrations in feathers would mirror Hg emission patterns in New York State and increase through time until 1980 then decrease thereafter in response to increased regulation of anthropogenic Hg emissions. We found that MeHg concentrations increased with δ¹⁵N, and that MeHg feather concentrations for some individuals from four of the six species examined exceeded concentrations known to cause negative sublethal effects in birds. In contrast to our prediction, MeHg concentrations in feathers did not parallel global or local Hg emissions through time and varied by species, even after controlling for possible changes in diet and habitat. MeHg concentrations varied substantially within species and individual specimens, suggesting that high within-individual variation in feather MeHg concentrations caused by spatiotemporal variation in molt, environmental Hg exposure, or mobility decoupling Hg uptake from breeding sites, may obscure trends in MeHg through time. Our study provides a unique assessment of feather MeHg in six species not typically analyzed using this retrospective approach.

Validation of an Alternative Feather Sampling Method to Measure Corticosterone

Simple Summary

Research projects on birds’ welfare or their stress physiology are often complemented by measurements of corticosterone level in feathers. Until now, the common standard for this method is to collect the feathers by plucking, a procedure which on living birds is presumed to be painful and to cause stress. Therefore, in most European countries an animal experiment application is required. The aim of this study was to validate an alternative, possibly less stressful sampling method: cutting the feathers close to the skin. The examined species were geese and ducks from a conventional poultry husbandry. There was no relevant difference between the two methods assessed according to statistical analysis. In conclusion, it is reasonable to assume that feather cutting could be established as an alternative sampling method for measuring corticosterone. Nevertheless, we recommend further research on other species to confirm these results.

Abstract

The most common feather sampling method for feather corticosterone measurement is by plucking the feathers from the bird’s skin. This procedure performed on living, restrained birds is qualified as an animal experiment according to German/European legislation, which has to be applied for from the competent authorities. The Directive 2010/63/EU requires the full implementation of the 3-R Principle of Russel and Burch in animal experiments, which means not only to replace the use of animals, but also to reduce the number of animals used and to refine procedures whenever possible. In response to this issue, the aim of this study was to validate an alternative, less invasive sampling method by cutting feathers close to the skin in comparison to the gold standard of plucking them. For this proof-of-principle study, a conventional poultry husbandry with trial groups of geese (Anser anser domesticus) and ducks (Anas sterilis) was selected. All birds were kept under the same living conditions to standardize the influencing factors regarding husbandry, and thus, their stress levels. Feather samples were collected between the shoulders from 46 geese and 51 ducks, both by cutting as well as by plucking, directly after slaughter for meat production. Feather corticosterone levels were measured with Enzyme-Linked Immunosorbent Assay (ELISA). Results were compared using Bland–Altman plots and concordance correlation coefficients (CCC). It could be seen that concordance between corticosterone levels in cut and plucked feathers was rather poor: 0.38 for Anser, and 0.57 for Anas. However, comparing the mean corticosterone values in pg/mm of each species with their respective standard deviations, the differences between the methods were negligible. As the results showed that the differences between the individuals were markedly greater than the differences between the methods, the determination of corticosterone levels in cut feathers is valid compared to using plucked feathers. The validation tests of ELISA showed only acceptable repeatability and reliability. Hence, the results should be verified in further studies. In conclusion, it is recommended for future research to use cut instead of plucked feathers for corticosterone measurement.

Songbird feathers as indicators of mercury exposure: high variability and low predictive power suggest limitations

Although feathers are commonly used to monitor mercury (Hg) in avian populations, their reliability as a sampling matrix has not been thoroughly assessed for many avian species, including most songbirds (Order Passeriformes). To better understand relationships between total Hg (THg) concentrations in feathers and other tissues for birds in the thrush and sparrow families, we (1) examined variation in THg concentrations among tissues, including feathers from six different tracts, nails, liver, and muscle; (2) tested relationships between THg concentrations in the various feather tracts and those in internal tissues from the same birds, to assess the predictive power of feather THg, and; (3) compared these relationships to those between THg concentrations in nails and internal tissues, to assess the viability of nails as a non-lethal sampling alternative. THg concentrations in all feather tracts and nails were consistently higher than those in the liver and muscle, and THg was higher in the thrushes than the sparrows. When comparing feather tracts, we observed high variation within some individuals, suggesting that estimates of Hg exposure could vary depending on which feather was sampled. Despite this variation, feather type had little effect on the predictive power of feather THg concentrations, which ranged from extremely weak in the sparrows (0.09 ≤ R² ≤ 0.16) to moderate (0.29 ≤ R² ≤ 0.42) in the thrushes. Alternatively, we found that nail samples better predicted internal tissue THg concentrations in both the thrushes (0.44 ≤ R² ≤ 0.48) and sparrows (0.70 ≤ R² ≤ 0.78). Nails have been used to monitor Hg in mammals and reptiles, but their reliability as a sampling matrix for monitoring Hg in avian populations has yet to be assessed for most taxa. While nails exhibit stronger relationships to internal tissue THg concentrations, they may not be an effective sampling option for all avian species because the collection of sizable nail samples could harm living birds, particularly small songbirds. However, this method may be reasonable for retrospective museum studies. Overall, our results suggest that, despite their current use in the literature, feathers are not a suitable sampling matrix for Hg monitoring in some songbird species.

Corticosterone in feathers of laying hens: an assay validation for evidence-based assessment of animal welfare

Studies indicate that the evaluation of animal welfare in birds may be carried out with the measurement of the stress-related hormone corticosterone in feathers. However a standardized procedure for corticosterone measurements in feathers is lacking, a validation needs to be carried out for each new species before implementation. The aim of the present study was to establish a valid method to measure corticosterone concentrations in feathers of laying hens in a precise and repeatable manner using an established and commercially available ELISA. Validation was performed with feather pools of tail and interscapular feathers of commercial Lohmann Brown laying hens. Assessment groups, consisting of 5 replicates, were created. All replicates of an assessment group were processed at the same time. Each replicate was run in 4 repetitions by ELISA. Intra-assay and interassay CV was 7.5 and 6.4%, respectively. The serial dilution showed linearity and parallelism. Examining the hormone extraction efficiency by using different methanol volumes resulted in no statistical differences (P > 0.05). Pulverized feathers showed higher corticosterone values than minced feathers (P > 0.05). Differences were shown between 2 feather types (tail vs. interscapular feathers; P < 0.05), as well as between vane and rachis (P < 0.05). Performance of a freeze-thaw cycle led to a decrease of corticosterone concentrations in the samples. A possible effect of UV-A radiation on the stability of corticosterone in the feathers was not found (P > 0.05). With the present study, a valid protocol, feasible for analyzing feather pools of laying hens, was developed. It may provide fundamentals for further investigations on corticosterone in feathers as a noninvasive indicator to evaluate aspects of animal welfare.

Exposure of a small Arctic seabird, the little auk (Alle alle) breeding in Svalbard, to selected elements throughout the course of a year

The Arctic marine ecosystem can be altered by processes of natural and anthropogenic origin. Spatio-temporal variation in species exposure to contamination is still poorly understood. Here, we studied elemental concentrations in the non-lethally collected samples from the most numerous seabird in European Arctic, the little auk (Alle alle) nesting in one breeding colony in Svalbard. This seabird spent the breeding season in the high-Arctic zone and the non-breeding period in sub-Arctic areas what may implicate spatio-temporal variation in elements bioaccumulation. We determined concentrations of 19 elements in adults feathers to determine levels of exposure during part of the pre-breeding (n = 74) and post-breeding (n = 74) seasons, feathers from nestlings (n = 18) to determine local contamination, and chick down (n = 16) and post-hatching eggshells (n = 18) to determine maternal input to offspring. During the pre-breeding period adults accumulated in their feathers significantly more Hg (one third of feathers exceeded the established toxicity threshold), Se and Mn compared to the post-breeding period. It reflects a higher exposition of birds to contaminants in pre-breeding moult areas outside the High Arctic compared to the post-breeding moult in the High Arctic. Sex differences in adult feathers representing the post-breeding period were found only for Ca and Zn with higher values in females. Chick down was characterized by high levels of several essential elements, an intermediate level of Hg and Se, and the highest Se:Hg molar ratios of all groups. Chick body feathers had the highest level of Cu and K among all the studied groups. Post-hatching eggshells were characterized by high Sr level (exceeding 2000 μg/g). Concentrations of several non-essential elements (Bi, Cd, Cr, Hg, Ni and Pb) in them were below method detection limits.

Methylmercury exposure in wildlife: A review of the ecological and physiological processes affecting contaminant concentrations and their interpretation

Exposure to methylmercury (MeHg) can result in detrimental health effects in wildlife. With advances in ecological indicators and analytical techniques for measurement of MeHg in a variety of tissues, numerous processes have been identified that can influence MeHg concentrations in wildlife. This review presents a synthesis of theoretical principals and applied information for measuring MeHg exposure and interpreting MeHg concentrations in wildlife. Mercury concentrations in wildlife are the net result of ecological processes influencing dietary exposure combined with physiological processes that regulate assimilation, transformation, and elimination. Therefore, consideration of both physiological and ecological processes should be integrated when formulating biomonitoring strategies. Ecological indicators, particularly stable isotopes of carbon, nitrogen, and sulfur, compound-specific stable isotopes, and fatty acids, can be effective tools to evaluate dietary MeHg exposure. Animal species differ in their physiological capacity for MeHg elimination, and animal tissues can be inert or physiologically active, act as sites of storage, transformation, or excretion of MeHg, and vary in the timing of MeHg exposure they represent. Biological influences such as age, sex, maternal transfer, and growth or fasting are also relevant for interpretation of tissue MeHg concentrations. Wildlife tissues that represent current or near-term bioaccumulation and in which MeHg is the predominant mercury species (such as blood and eggs) are most effective for biomonitoring ecosystems and understanding landscape drivers of MeHg exposure. Further research is suggested to critically evaluate the use of keratinized external tissues to measure MeHg bioaccumulation, particularly for less-well studied wildlife such as reptiles and terrestrial mammals. Suggested methods are provided to effectively use wildlife for quantifying patterns and drivers of MeHg bioaccumulation over time and space, as well as for assessing the potential risk and toxicological effects of MeHg on wildlife.

Feather Corticosterone Measurements of Greater Flamingos Living under Different Forms of Flight Restraint

Deflighting zoo birds is a practice that receives increasing criticism due to its presumed incompatibility with animal welfare. To our knowledge, this is the first approach to address this problem in a scientific way. To do this, we compared feather corticosterone (CORTf) from Greater Flamingos (Phoenicopterus roseus, n = 151) of different flight status (i.e., pinioned, feather clipped, airworthy) from twelve different zoological institutions. To complement the hormone measurements, behavioral observations (scan samplings) were conducted prior to feather sampling within the presumed time frame of feather growth. We hypothesized that CORTf of the deflighted flamingos would differ from CORTf of their airworthy conspecifics. No significant difference in CORTf was found between the three groups, and our hypothesis was rejected. However, the impact of the institution itself (i.e., the housing conditions) proved to be the most dominant variable (variance between the institutions = 53.82%). Due to high variability, the behavioral observations were evaluated descriptively but did not give rise to doubt the findings in CORTf. Therefore, we assume that the method of flight restraint of Greater Flamingos does not have a measurable effect on CORTf. We consider this model for evaluating animal welfare of zoo birds a useful tool and provide ideas for further adjustments for consecutive studies.

Temporal trends of mercury differ across three northern white-tailed eagle (Haliaeetus albicilla) subpopulations

The spatiotemporal trends of mercury (Hg) are crucial for the understanding of this ubiquitous and toxic contaminant. However, uncertainties often arise from comparison among studies using different species, analytical and statistical methods. The long-term temporal trends of Hg exposure were reconstructed for a key sentinel species, the white-tailed eagle (Haliaeetus albicilla). Body feathers were sampled from museum collections covering 150 years in time (from 1866 to 2015) from West Greenland (n = 124), Norway (n = 102), and Sweden (n = 87). A significant non-linear trend was observed in the Norwegian subpopulation, with a 60% increase in exposure occurring from 1866 to 1957 followed by a 40% decline until 2015. In the Swedish subpopulation, studied at a later period, the Hg exposure showed a drastic decline of 70% from 1967 to 2011. In contrast, no significant trend could be observed in the Greenland subpopulation. The additional analysis of dietary proxies (δ¹³C and δ¹⁵N) in general increased performance of the temporal trend models, but this was dependent on the subpopulation and study period. The downward trend of Hg coincided with the decreasing δ¹³C and δ¹⁵N in the Norwegian subpopulation, suggesting a potential dietary mitigation of Hg contamination. Hg exposure in both the Greenland and Norwegian subpopulations was consistently below the suggested threshold for adverse health effects (40.0 μg g^-1), while the maximum exposure in the Swedish subpopulation was distinctively elevated (median: 46.0 μg g^-1) and still remains well above natural background concentrations (maximum 5.0 μg g^-1).

Accumulation of trace elements in feathers of the Kentish plover Charadrius alexandrinus

A non-invasive study of trace element accumulation in tail feathers of the Kentish plover (Charadrius alexandrinus) was performed along the coastline of the northern littoral strip of the Venice Lagoon, with the aim to verify whether contamination may be a factor affecting conservation status of Kentish plover populations. Body burdens in feathers of 11 trace elements including toxic metals/metalloids and essential elements (As, Cd, Co, Cr, Cu, Hg, Ni, Pb, Se, V, Zn) were quantified by ICP-MS, then concentrations were normalized to feather's age calculated using ptilochronology in order to obtain daily deposition rates. Mercury emerged as a major threat to the conservation of the species, since average feather concentration was clearly above the adverse-effect threshold associated with impairment in the reproductive success in a number of bird species. Also Cd and Se occurred at levels that may impact on the conservation status of the studied species at local scale, even if to a lesser extent than Hg. Gender-related differences in trace element accumulation emerged only for As, although for this element the risks associated to environmental exposure seem to be negligible.

Mercury Concentrations Vary Within and Among Individual Bird Feathers: A Critical Evaluation and Guidelines for Feather Use in Mercury Monitoring Programs

Feathers are widely used to represent mercury contamination in birds. Yet, few recommendations exist that provide guidance for using bird feathers in mercury monitoring programs. We conducted a literature review and 5 experiments to show that mercury concentrations vary substantially within (vane >100% higher than calamus) and among (>1000%) individual feathers from the same bird. We developed a research tool and guidelines for using bird feathers for mercury studies based on 3 components: 1) variability of feather mercury concentrations within an individual bird (coefficient of variation), 2) desired accuracy of the measured mercury concentration, and 3) feather and bird mass. Our results suggest a general rule that if the goal is to limit analytical and processing costs by using whole feathers in only one sample boat, then to achieve an accuracy within 10% of a bird's overall average feather mercury concentration a bird with a coefficient of variation ≤10% must be <190 g (size of a large shorebird). To achieve an accuracy within 20%, a bird with a coefficient of variation ≤10% must be <920 g (a large duck). When more than one sample boat is needed to fit the required number of feathers to achieve the desired accuracy, the results suggest homogenizing feathers and analyzing an aliquot of ≥20 mg for mercury. The present study suggests increasing the number of feathers typically used per bird to assess mercury concentrations. Environ Toxicol Chem 2019;38:1164-1187. Published 2019 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Detecting fluoxetine and norfluoxetine in wild bird tissues and feathers

The contamination of the environment with human pharmaceuticals is widespread and demand for such products is mounting globally. Wild vertebrates may be at particular risk from any effects from pharmaceuticals, because of the evolutionary conservation of drug targets. However, exposure of wildlife to pharmaceuticals is poorly characterised, partly due to challenges associated with detecting rapidly metabolised compounds. As part of a wider study on the behavioural effects of fluoxetine (Prozac) on Eurasian starlings (Sturnus vulgaris), we investigated which avian samples are best suited for detecting exposure to fluoxetine in free-living birds. We analysed plasma, various tissues and tail feathers (grown both in the wild and in captivity during the dosing period) from fluoxetine-treated birds (dosed daily with 0.035 mg kg^-1 bodyweight for 28 weeks), and liver tissue and tail feathers from sham-dosed birds. We detected fluoxetine in only two of twelve plasma samples from dosed birds. In dosed birds, median concentrations of free fluoxetine/norfluoxetine in tissues (two hour post-final dose) were: 111.2/67.6 ng g^-1 in liver, 29.6/5.7 ng g^-1 in kidney, 14.2/4.0 ng g^-1 in lung, 15.1/1.6 ng g^-1 in brain. We estimated that fluoxetine would remain detectable in liver and kidney approximately 4.5 times longer (90 h) than in brain (20h). In dosed birds, fluoxetine was detected in feathers regrown during the dosing period (median concentration = 11.4 ng g^-1) at concentrations significantly higher than in regrown feathers from control birds. Fluoxetine residues were detected in wild-grown feathers (grown before the birds were brought into captivity) at concentrations up to 27.0 ng g^-1, providing some evidence of likely exposure in the wild. Our results show liver and kidney can be used for detecting fluoxetine in avian carcasses and provide a first indication that feathers may be useful for assessing exposure to fluoxetine, and possibly other pharmaceuticals.

Analysis of 11 trace elements in flight feathers of Italian Sparrows in southern Italy: A study of bioaccumulation through age classes, variability in three years of sampling, and relations with body condition

Trace elements have been acknowledged as one of the subtlest environmental hazards in all compartments of the total environment. Enhanced by activities in the anthroposphere, they accumulate in the atmosphere, lithosphere, and hydrosphere. Eventually, trace elements can bioaccumulate or biomagnifiy in the biosphere, with harmful effects on animals occupying higher trophic levels, including humans. Accordingly, there is great interest in assessing and monitoring trace element concentrations in the biosphere, and birds, especially passerines, have been commonly chosen as biomonitors. In this study, the concentration of 11 trace elements was measured (i.e. aluminum, chromium, manganese, iron, nickel, copper, zinc, arsenic, cadmium, barium, and lead) in flight feathers of Italian Sparrows, a common bird species hitherto not analysed in this respect. Samples were collected in an agricultural area in southern Italy, where a mosaic of natural environments, urbanized areas and industrial facilities can be found. Linear mixed modelling was applied to the analysis of flight feathers in juveniles, juvenile birds moulting to adulthood, and adults in three sampling years on 184 birds. Results are timely as they add new data to the scarce available information on Ba and As in bird feathers and showed clear bioaccumulation patterns from juveniles to adults for As, Cr, and Cd. Moreover, the modelling approach showed that the concentration of elements such as As, Cd and Cr can be variable across the years and that some elements, notably Cd and Ba, were inversely correlated with body mass and wing length, respectively, suggesting potential negative effects on bird health. Finally, when modelling bird body condition and trace elements, results showed that Cd and Ba negatively affect birds regardless of age or sampling year. Thus, the Italian Sparrow could be considered as a valuable biomonitor for trace elements in the total environment, especially for Cd and Ba.

Exposure to Pb impairs breeding success and is associated with longer lifespan in urban European blackbirds

Although several factors have been highlighted to explain the influence of urbanization on bird fitness and survival, the role of persistent toxicants such as lead (Pb), which is typically present in urban areas worldwide, has seldom been studied despite the ecological importance of such a widespread stressor. Studying free-living European blackbirds (Turdus merula) in city parks, we tested the hypothesis that low-dose chronic exposure to Pb could shape the life-history traits of urban birds. The feather concentrations of Pb and cadmium were typical of urban areas and low-to-moderate contamination of sites. Although the lifetime breeding success of females decreased with increasing exposure to Pb, the lifespan and survival probabilities of blackbirds increased with Pb contamination regardless of gender. Breeding effort-dependent patterns in the relationship between lifespan and Pb levels were highlighted. No significant relationships were detected between cadmium and life-history traits. The results suggest a possible trade-off between self-maintenance and reproduction, with the most affected birds redirecting allocations towards their own survival, which is consistent with the “stress hormone hypothesis”. These findings suggest that Pb pollution in urban environments may shape avian ecological features and be one of the drivers of wildlife responses to urbanization and that some urban areas may function as ecological traps driven by pollutants.

Determination of testosterone and corticosterone in feathers using liquid chromatography-mass spectrometry

Feathers gradually accumulate hormones and reflect long-term average plasma steroid levels during their growth. Feather hormone levels thus provide for the measurement of plasma hormones concentrations integrated over a period of several days or weeks. In this study, we focused on the development of a method to determine testosterone (TEST) and corticosterone (CORT) levels in extracts from feathers of small bodied birds with a limited amount of feathers available per individual. For this purpose, the method had to be verified for a small weight of samples. The present study describes the effect of the conditions of sample preparation and keto-derivatisation on the sensitivity of the LC-ESI-MS/MS analysis of TEST and CORT. Generally, chemical derivatization improves the sensitivity and selectivity of LC-MS/MS analysis. It can be used particularly in situations when the total amount of collected sample is limited (such as in our studies). Both the conditions of feather sample preparation (the selection of the extraction solvent, the time of extraction, and the conditions of solid phase extraction) and the reaction conditions affecting the formation of keto-derivatives (such as reaction temperature and reaction time) were tested. Methanol as the extraction solvent, 8 h as the extraction time, 50 °C as the reaction temperature of derivatization, and 90 min as the reaction time of derivatization are the most suitable conditions in terms of achieving a high sensitivity of analyses. Calibration curves are linear, at least in the range 25-2500 pg mL^-1, which is usually found in feather extracts. The limit of detection (LOD) for TEST and CORT was 1.0 and 0.3 pg per mL, respectively. The limit of quantification (LOQ) for TEST and CORT was 3.3 and 1.0 pg per mL, respectively. The optimized procedure was successfully applied for the analysis of TEST and CORT in real feather samples. The method could be used in a variety of research direction including wildlife, agricultural or veterinary studies.

Using a keratinase to degrade chicken feathers for improved extraction of glucocorticoids

Stress in animals is a concern in conservation breeding programs and livestock production facilities. The biological stress response is mediated by the release of glucocorticoids, which can suppress reproduction, growth, and immunity if recurrently activated. Feathers can be used to extract and monitor concentrations of corticosterone, a primary glucocorticoid in birds. However, current techniques for extracting feather corticosterone present challenges, including difficulty assessing extraction efficiency or hormone recovery, inconsistent extraction across feather lengths or pieces, and several uncertainties regarding the mechanisms of hormone deposition into feathers. To overcome such challenges and to provide tools useful for facilitating conservation breeding and livestock production, we developed and validated an alternative procedure for extracting feather glucocorticoids. We first developed a protocol to enzymatically digest the protein matrix of feathers using a keratinase, such that non-protein analytes could be isolated by organic extraction. We then developed an extraction protocol and evaluated techniques by measuring extraction efficiency and by testing parallelism and hormone recovery (accuracy) using radioimmunoassay. Our results demonstrated high and consistent extraction efficiency, as well as high accuracy and reliable parallelism to a standard curve upon measurement of corticosterone concentrations from extracts. By dissolving feather material into solution prior to extraction, we were able to replicate hormone deposition into the feather matrix and ensure consistent extraction across feathers. This work provides additional support for the validity and practicality of extracting glucocorticoids from feathers. Our extraction protocol is likely to extend to other applications as well, including the isolation of numerous non-protein analytes from various keratinized tissues.

Assessment of Commercially Available Immunoassays to Measure Glucocorticoid Metabolites in African Grey Parrot (Psittacus Erithacus) Droppings: A Ready Tool for Non-Invasive Monitoring of Stress

Simple Summary

The African Grey Parrot is a very popular bird commonly found in zoological collections. However, captivity can prevent it from meeting its natural needs and so become an ongoing stressor, leading sometimes to clinical and/or behavioral disorders. Non-invasive forms of stress assessment are of definite interest for monitoring welfare in captive bird populations. One notable stress outcome is the excretion of glucocorticoid metabolites (from the stress hormone corticosterone) in droppings. The aim of this study was to carefully assess methods of glucocorticoid metabolites extraction and measurement in droppings from African Grey Parrots. Several extraction and enzyme immunoassays procedures were tested, based on the evaluation of analytical quality parameters and biological relevance. The best procedure was found to be a combination of a 60% methanol extraction with the use of a commercial corticosterone enzyme immunoassay. To determine whether this method was suitable for assessing different stress levels, a significant correlation with another reliable stress marker in birds, the Heterophil: Lymphocyte Ratio, was evidenced. This method can thus be used to evaluate stress in African Gray Parrots in a non-invasive way and help to monitor their welfare in zoo populations for instance.

Abstract

Despite being undomesticated, African Grey Parrots (Psittacus erithacus) are commonly found in captivity, in zoos or as pets. Captivity can be an ongoing stressor. Non-invasive glucocorticoid metabolites (GCM) measurements from bird droppings are of interest for assessing stress but require careful evaluation in each newly studied species. This study describes the assessment of such methods for Psittacus erithacus to provide tools for evaluating stress and monitoring welfare. We evaluated 12 method combinations of GCM extraction and enzyme immunoassay (EIA) from a pool of African Grey Parrot droppings, through the validation of several analytical parameters. Then, Heterophil: Lymphocyte Ratios (HLR), another reliable stress marker, were determined and correlated to individual dropping GCM concentrations for 29 birds to determine whether the method is biologically relevant. We found that the best procedure to measure GCM in African Grey Parrot droppings is a combination of 60% methanol extraction measured using a Corticosterone EIA kit (Cayman Chemical Company) from fresh or dry droppings. The establishment of a significant correlation (Pearson coefficient correlation = 0.48; p = 0.0082) between HLR and GCM in the studied population confirmed the method biological relevance. This method can thus be applied to assess stress in Psittacus erithacus and support welfare monitoring in zoo populations.

Do wild-caught urban house sparrows show desensitized stress responses to a novel stressor?

While urbanization exposes individuals to novel challenges, urban areas may also constitute stable environments in which seasonal fluctuations are buffered. Baseline and stress-induced plasma corticosterone (cort) levels are often found to be similar in urban and rural populations. Here we aimed to disentangle two possible mechanisms underlying such pattern: (i) urban environments are no more stressful or urban birds have a better ability to habituate to stressors; or (ii) urban birds developed desensitized stress responses. We exposed wild-caught urban and rural house sparrows (Passer domesticus) to combined captivity and diet treatments (urban versus rural diet) and measured corticosterone levels both in natural tail feathers and in regrown homologous ones (cort_f). Urban and rural house sparrows showed similar cort_f levels in the wild and in response to novel stressors caused by the experiment, supporting the growing notion that urban environments are no more stressful during the non-breeding season than are rural ones. Still, juveniles and males originating from urban populations showed the highest cort_f levels in regrown feathers. We did not find evidence that cort_f was consistent within individuals across moults. Our study stresses the need for incorporating both intrinsic and environmental factors for the interpretation of variation in cort_f between populations.

Summary: Corticosterone in natural and regrown feathers was similar between urban and rural birds. Sex and age related to corticosterone in regrown feathers. Feather corticosterone was not consistent across different moults.

Selection of tawny owl (Strix aluco) flight feather shaft for biomonitoring As, Cd and Pb pollution

In this study, we determined the concentrations of As, Cd and Pb in the shaft of all primary flight feathers from ten tawny owl (Strix aluco) specimens, with the aim of selecting which shaft of the corresponding primary feather should be used in biomonitoring surveys to enable inter-individual comparisons of the levels of these metals. The birds had died between 2006 and 2013 and their bodies were stored in the various Wildlife Recovery Centres in Galicia (NW Spain). The analyses revealed a high degree of inter-shaft variability, mainly in the concentrations of As and Cd. However, it was possible to identify the most representative samples in each case: for As, the shaft of primary flight feather number 5 (S5) (which represented 11% of the total As excreted in all of the primary flight feathers); for Cd, the shaft of primary flight feather number 2 (S2) (11% of the total excreted); and for Pb, the shaft of primary flight feather number 8 (S8) (14% of the total excreted). However, the difficulties associated with the analytical determination of these pollutants in the shaft should be taken into account when this technique is applied in biomonitoring studies.

Elemental composition in feathers of a migratory passerine for differentiation of sex, age, and molting areas

The bulk analysis of single feathers of 263 feathers belonging to 238 individuals of a migratory passerine (collared flycatcher, Ficedula albicollis, originating from a breeding population in the Pilis-Visegrád Mountains in Hungary) by inductively coupled plasma sector field mass spectrometry (ICP-SF-MS) for determination of elements after proper dissolution allowed the quantitative determination of 38 elements. Calcium, Mg, Mn, Fe, and Zn were found to have a quantitative determination frequency larger than 80 % and a concentration greater than 100 μg/g. Among ecotoxicologically relevant elements, Ni, Cd, Hg, and Pb could be determined in more than 55 % of the tail feather samples. The concentration of Hg with a quantification limit of 0.006 μg/g and Pb with that of 0.015 μg/g was higher than 1 and 10 μg/g, respectively, in more than 80 % of the investigated samples, but generally lower than levels that could cause adverse behavioral effects. The principal component analyses of elemental concentration data followed by the application of general linear models revealed that, for male collared flycatchers, the concentration of Sn, Pb, Ni, Sr, Mg, Zn, Ba, and Sc differed significantly in the wing and tail feathers collected from the same individuals. With females, only the Ca and Sc concentration showed a significant difference between wing and tail feathers. Moreover, the concentration of rare earth elements, V, Fe, Sr, Mg, Mn, Zn, Pb, and Ba in tail feathers allowed differentiation between sexes while the concentration of Se, Bi, and Sc between yearling and adult male individuals. At the same time, Sc differentiated age categories in females. Distribution of major elements along the rachis of feathers could be monitored by laser ablation ICP-SF-MS after normalization of the intensities to either ¹³C or ³⁴S signals.

Quantifying corticosterone in feathers: validations for an emerging technique

Feather corticosterone measurement is becoming a widespread tool for assessing avian physiology. Corticosterone is deposited into feathers during growth and provides integrative and retrospective measures of an individual's hypothalamic-pituitary-adrenal (HPA) axis function. Although researchers across disciplines have been measuring feather corticosterone for the past decade, there are still many issues with the extraction and measurement of corticosterone from feathers. In this paper, we provide several directives for refining the methodology for feather hormone analysis. We compare parallelism between the standard curve and serially diluted feather tissue from wild turkeys, Canada jays, and black-capped chickadees to demonstrate the wide applicability across species. Through a series of validations, we compare methods for feather preparation, sample filtration and extract reconstitution prior to corticosterone quantification using a radioimmunoassay. Higher corticosterone yields were achieved following pulverization of the feather however, more variation between replicates was observed. Removal of the rachis also increased the amount of corticosterone detected per unit mass while glass versus paper filters had no effect, and using ethanol in the reconstution buffer decreased intra-assay variation. With these findings and continued methodological refinement, feather corticosterone has the potential to be a powerful tool for both ecologists and physiologists working with historical and contemporary specimens.

Retrospective biomonitoring of mercury and other elements in museum feathers of common kestrel Falco tinnunculus using instrumental neutron activation analysis (INAA)

This study examines the potential to use instrumental neutron activation analysis (INAA) to explore temporal and geographical variation in exposure to heavy metals and other selected elements in common kestrel Falco tinnunculus using feathers from a natural history collection. The study gathered samples of two breast feathers from each of 16 adult male kestrel specimens from Naturalis Biodiversity Centre, collected in The Netherlands between 1901 and 2001. Feather samples were analysed for more than 50 elements, using INAA at the Reactor Institute Delft. Results (in mg/kg dw) were transformed into ratios of milligram of element per millimetre of feather length. The distribution of the mass fractions and ratios was plotted for each element against time and by geographical area. Observed mass fractions and/or ratios are discussed for selected elements (Hg, Cd, Zn, Pt, Pd, Se, Al, Rb, As, Sb, Cr, V, Cl, Br) known to have, at certain concentrations, adverse effects on raptors. Some samples show mass fractions of certain elements (Cr, Cd, Se, As) above levels known to have adverse effects. We conclude that the analysis of museum feathers using INAA provides reference values for concentrations of selected elements, including those of high societal concern such as Hg and Cd, against which to assess concentrations of these elements in feathers of present-day living raptor populations.

Supplementary feeding increases nestling feather corticosterone early in the breeding season in house sparrows

Several studies on birds have proposed that a lack of invertebrate prey in urbanized areas could be the main cause for generally lower levels of breeding success compared to rural habitats. Previous work on house sparrows Passer domesticus found that supplemental feeding in urbanized areas increased breeding success but did not contribute to population growth. Here, we hypothesize that supplementary feeding allows house sparrows to achieve higher breeding success but at the cost of lower nestling quality. As abundant food supplies may permit both high‐ and low‐quality nestlings to survive, we also predict that within‐brood variation in proxies of nestling quality would be larger for supplemental food broods than for unfed broods. As proxies of nestling quality, we considered feather corticosterone (CORT_f), body condition (scaled mass index, SMI), and tarsus‐based fluctuating asymmetry (FA). Our hypothesis was only partially supported as we did not find an overall effect of food supplementation on FA or SMI. Rather, food supplementation affected nestling phenotype only early in the breeding season in terms of elevated CORT_f levels and a tendency for more variable within‐brood CORT_f and FA. Early food supplemented nests therefore seemed to include at least some nestlings that faced increased stressors during development, possibly due to harsher environmental (e.g., related to food and temperature) conditions early in the breeding season that would increase sibling competition, especially in larger broods. The fact that CORT_f was positively, rather than inversely, related to nestling SMI further suggests that factors influencing CORT_f and SMI are likely operating over different periods or, alternatively, that nestlings in good nutritional condition also invest in high‐quality feathers.

Exposure, Effects and Absorption of Lead in American Woodcock (Scolopax minor): A Review

Due to long term declines of American Woodcock (Scolopax minor) and widespread distribution of environmentally available lead (Pb) throughout their geographic range, it is important to assess if Pb exposure is a potential contributor to these declines. Woodcock are exposed to Pb through various environmental sources and are known to exhibit relatively high bone-Pb concentrations. Absorption of Pb by birds, and woodcock specifically, is not well understood. Some studies show that interactions among calcium, phosphorus, iron, zinc, and vitamin D levels may play an important role in Pb absorption. Therefore, when future Pb studies are performed for woodcock, and other birds, interactions among these elements should be considered. For example, these interactions are relevant in the acquisition and mobilization of calcium in female birds during egg development and shell calcification. These factors should be considered to understand potential mechanisms of Pb exposure, Pb absorption, and subsequent Pb toxicity to birds in general, and woodcock specifically. This review discusses Pb exposure routes, effects of Pb toxicity, and the distribution of Pb in American woodcock and identifies areas for future research in woodcock and other avian species.

The Topobiology of Chemical Elements in Seabird Feathers

The highly organized morphogenesis of bird feathers holds important phylo- and ontogenetic information on the evolution of birds, organogenesis, tissue regeneration, and the health status of individual animals. Altered topobiological patterns are regularly used as retrospective evidence for disturbed developmental trajectories due to the past exposure to environmental stressors. Using the most advanced high-resolution (5–70 µm) X-ray fluorescence microscopy (XFM), we describe in the feathers from three species of Procellariiformes hitherto unknown, depositions of elements (Zn, Ca, Br, Cu, Fe) that are independent of pigmentation or any underlying variation in density or polymer structure. In the case of Zn, the pattern across several species of Procellariiformes, but not other species, consisted of highly regular bands of Zn numbering 30–32, which may reflect the estimated number of days of active feather growth or the duration of the moult period. Thus, speculatively, the highly consistent Zn pattern might be the result of a so far unknown diurnal systemic regulation rather than local heterogeneity amongst the follicular stem cells.

The effect of social group size on feather corticosterone in the co-operatively breeding Smooth-billed Ani (Crotophaga ani): An assay validation and analysis of extreme social living

Living closely with others can provide a myriad of fitness benefits, from shared territory defense to co-operative resource acquisition. Costs of social aggregation are not absent, however, and likely influence optimal and observed groups’ sizes in a social species. Here, we explored optimal group size in a joint-nesting cuckoo species (the Smooth-billed Ani, Crotophaga ani) using endocrine markers of stress physiology (corticosterone, or CORT). Smooth-billed Anis exhibit intense reproductive competition that is exacerbated in atypically large groups. We therefore hypothesized that intra-group competition (measured by social group size) mediates the desirability and physiological cost of social group membership in this species. To test this hypothesis, we captured 47 adult Smooth-billed Anis (31 males, 16 females) during the breeding seasons of 2012-2014 in south-western Puerto Rico, and documented social group sizes. Tail feathers were sampled and used to quantify CORT (pg/mg) in enzyme-linked immunosorbent assays (ELISAs) (n = 50). Our analyses show significant differences in feather-CORT of adults between categorical group sizes, with individuals from atypically large social groups (≥ x + 1SD) having highest mean concentrations (33.319 pg/mg), and individuals from atypically small social groups (≤ x − 1SD) having lowest mean concentrations (8.969 pg/mg). Whether reproductive competition or effort is responsible for elevated CORT in atypically large social groups, however, remains unclear. Our results suggest that living in atypically large groups is physiologically expensive and may represent an evolutionarily unstable strategy. To our knowledge, this is the first study to explore a correlation between stress physiology and group size in a joint-nesting species.

The first exposure assessment of legacy and unrestricted brominated flame retardants in predatory birds of Pakistan

The exposure to legacy polybrominated diphenyl ethers (PBDEs), hexabromocyclododecanes (HBCDDs) and unrestricted 1,2-bis (2,4,6-tribromophenoxy) ethane (BTBPE), bis (2-ethylhexyl)-2,3,4,5-tetrabromophthalate (BEH-TEBP) and 2-ethylhexyl-2,3,4,5-tetrabromo-benzoate (EH-TBB) was examined in tail feathers of 76 birds belonging to ten predatory species inhabiting Pakistan. In addition, different feather types of six individuals of Black kite (Milvus migrans) were compared for their brominated flame retardant (BFR) levels. Black kite was found to be the most contaminated species with a median (minimum-maximum) tail feather concentration of 2.4 (0.70-7.5) ng g^-1 dw for ∑PBDEs, 1.5 (0.5-8.1) ng g^-1 dw for ∑HBCDDs and 0.10 (<LOQ-0.1) ng g^-1 dw for BTBPE. Among unrestricted BFRs, BTBPE was detected only in Black kite and Little owl (Athene noctua), whereas BEH-TEBP and EH-TBB were not detected in any species. BDE-47 was found to be the most prevalent BFR compound in aquatic species, while BDE-99 and -153 were more abundant in terrestrial species. For HBCDDs, α-isomer was generally recorded as the most prevalent BFR in both terrestrial and aquatic species. The concentrations of BFRs differed significantly (all P < 0.01) among species, trophic guilds and between habitats, the latter for PBDEs only (P < 0.04), whereas differences among taxonomic affiliations and groups with different feeding regimes were not significant (P > 0.05 for both). Similarly, no significant concentration differences were observed among different feather types (all P > 0.05) suggesting their similar exposure. While variables such as species, trophic guild and δ¹⁵N values were evaluated as major predictors for BFR accumulation in the studied species, we predict that combined effects of just mentioned factors may govern the intra- and interspecific differences in BFR contamination profiles. We urge for further investigation of BFR exposure and potential toxicological effects in predatory birds from Asia with a more extensive sample size per species and location.

Temporal overlap and repeatability of feather corticosterone levels: practical considerations for use as a biomarker

The measurement of corticosterone (CORT) levels in feathers has recently become an appealing tool for the conservation toolbox, potentially providing a non-invasive, integrated measure of stress activity throughout the time of feather growth. However, because the mechanism of CORT deposition, storage and stability in feathers is not fully understood, it is unclear how reliable this measure may be, especially when there is an extended interval between growth and feather collection. We compared CORT levels of naturally grown feathers from tree swallows (Tachycineta bicolor) that were moulted and regrown concurrently and therefore expected to have similar CORT levels. Specifically, we compared the same feather from the left and right wing (moulted symmetrically) and different types of feathers (wing, back and tail) expected to have been moulted within the same time period. We found that larger, heavier feathers held more CORT per unit length. In addition, we found a lack of concordance in CORT levels both within the same feather type and between different feather types, even after taking into account differences in feather density. Our results indicate that naturally grown feathers may not consistently provide an indication of stress status. Additionally, conflict in results may arise depending on the feather assayed, and total feather volume may be an important consideration when interpreting feather CORT levels. Future work is necessary to determine explicitly the mechanisms of CORT deposition, the effects of environmental exposure and feather wear on the permanence of the feather CORT signal, and the influence of responses to wild stressors on feather CORT levels, before feather CORT can be implemented effectively as a tool for ecological and conservation applications.

Use of feathers to assess polychlorinated biphenyl and organochlorine pesticide exposure in top predatory bird species of Pakistan

Little is known about the levels of organochlorines (OCs) in predatory bird species from Asia or the factors governing their concentrations. This study is the first report on concentrations of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in predatory birds of Pakistan. The concentrations of PCBs and OCPs were investigated using tail feathers of ten different species of predatory birds. In addition, concentration differences among body, tail, primary and secondary feathers were investigated for six individuals of black kite (Milvus migrans). Ranges of concentrations were highest for dichlorodiphenyldichloroethylene (p,p'-DDE: 0.11-2163ngg(-1) dry wt.) followed by dichlorodiphenyltrichloroethane (p,p'-DDT: 0.36-345ngg(-1) dry wt.), hexachlorobenzene (HCB: 0.02-34ngg(-1) dry wt.), ∑PCBs (0.03-16ngg(-1) dry wt.) and trans-nonachlor (TN; 0.01-0.13ngg(-1) dry wt.). CB 118, 153, 138, and 180 along with p,p'-DDE were found as the most prevalent compounds. ∑PCBs and ∑DDTs were significantly different among species (both p<0.01) and omnivorous, scavengers, carnivorous and piscivorous trophic guilds (all p<0.03). Only ∑PCBs were significantly differentamong different families of birds (p<0.01). Values of stable isotopes (δ(13)C and δ(15)N) differed significantly (all p<0.01) among species, families, trophic guilds as well as terrestrial and aquatic habitat but not between nocturnal and diurnal predators (p=0.22 for δ(13)C; p=0.50 for δ(15)N). Concentrations of ∑PCBs, ∑DDTs and trans-nonachlor, but not HCB (p=0.86), were significantly different among different feather types (all p<0.01). Trophic and taxonomic affiliation as well as dietary carbon sources (δ(13)C) for species were identified as the variables best explaining the observed variation in exposure to the studied compounds. The significance of contributing factors responsible for OC contamination differences in predatory birds should be further elucidated in future studies.