Identifying the African wintering grounds of hybrid flycatchers using a multi-isotope (δ2H, δ13C, δ15N) assignment approach

Genetics and Evolution of Bird Migration

Bird migration has long been a subject of fascination for humankind and is a behavior that is both intricate and multifaceted. In recent years, advances in technology, particularly in the fields of genomics and animal tracking, have enabled significant progress in our understanding of this phenomenon. In this review, we provide an overview of the latest advancements in the genetics of bird migration, with a particular focus on genomics, and examine various factors that contribute to the evolution of this behavior, including climate change. Integration of research from the fields of genomics, ecology, and evolution can enhance our comprehension of the complex mechanisms involved in bird migration and inform conservation efforts in a rapidly changing world.

The association between haemosporidian infection and non-breeding moult location in great reed warblers revisited by combining feather stable isotope profiles and geolocator data

Stable isotope analysis provides valuable insights into the ecology of long-distance migratory birds during periods spent away from a specific study site. In a previous study, Swedish great reed warblers (Acrocephalus arundinaceus) infected with haemosporidian parasites differed in feather isotope ratios compared to non-infected birds, suggesting that infected and non-infected birds spent the non-breeding season in different locations or habitats. Here, we use a novel dataset comprising geolocator data, isotopes, and haemosporidian infection status of 92 individuals from four Eurasian populations to investigate whether parasite transmission varies with geography or habitats. We found that the probability of harbouring Plasmodium and Leucocytozoon parasites was higher in birds moulting in the eastern region of the non-breeding grounds. However, no geographic pattern occurred for Haemoproteus infections or overall infection status. In contrast to the previous study, we did not find any relationship between feather isotope ratios and overall haemosporidian infection for the entire current dataset. Plasmodium-infected birds had lower feather δ15N values indicating that they occupied more mesic habitats. Leucocytozoon-infected birds had higher feather δ34S values suggesting more coastal sites or wetlands with anoxic sulphate reduction. As the composition and prevalence of haemosporidian parasites differed between the old and the current dataset, we suggest that the differences might be a consequence of temporal dynamics of haemosporidian parasites. Our results emphasize the importance of replicating studies conducted on a single population over a restricted time period, as the patterns can become more complex for data from wider geographical areas and different time periods.

A feather hydrogen (δ2H) isoscape for Brazil

Spatial patterns of stable isotopes in animal tissues or “isoscapes” can be used to investigate animal origins in a range of ecological and forensic investigations. Here, we developed a feather hydrogen isotope (δ²H_f) isoscape for Brazil based on 192 samples of feathers from the family Thraupidae from scientific collections. Raw values of δ²H_f ranged from -107.3 to +5.0‰, with higher values at the Caatinga biome (northeast Brazil) and lower values at the Amazon and Pantanal. A Random Forest (RF) method was used to model the spatial surface, using a range of environmental data as auxiliary variables. The RF model indicated a negative relationship between δ²H_f and Mean Annual Precipitation, Precipitation in the Warmest Quarter, and Annual Temperature Range and positive relationships for amount-weighted February-April precipitation δ²H (δ²H_p(Feb-April)) and Mean Annual Solar Radiation. Modelled δ²H_f values ranged from -85.7 to -13.6‰. Ours is the first δ²H_f isoscape for Brazil that can greatly assist our understanding of both ecological and biogeochemical processes controlling spatial variation in δ²H for this region. This isoscape can be used with caution, due to its poor predictive power (as found in other tropical regions) and can benefit from new sample input, new GNIP data, ecological and physiological studies, and keratin standard material better encompassing the range in feather samples from Brazil. So, we encourage new attempts to build more precise feather H isoscapes, as well as isoscapes based on other elements.

Feather stable isotopes (δ2Hf and δ13Cf) identify the Sub-Saharan wintering grounds of turtle doves from Europe

Conservation of migratory birds requires knowledge of breeding and nonbreeding ranges and the connections between them. European turtle doves (Streptopelia turtur) are Palearctic-African long-distance migrants with wintering areas in the Sub-Saharan belt that are classed as vulnerable due to strong population declines. However, detailed non-breeding locations of individuals from different migratory flyways are unknown. To identify wintering regions of turtle doves, we measured stable isotopes of feathers grown on the wintering grounds and used a dual-isotope (hydrogen (δ2Hf) and carbon (δ13Cf)) probabilistic assignment to analyse origins of individuals migrating through the western and central/eastern flyways. The most probable wintering areas for turtle dove samples from both flyways were in the western and central Sub-Sahara. However, we found differences in δ2Hf and δ13Cf values between turtle doves following different migratory routes (western vs central/eastern flyway). This result suggests a higher likelihood of origins in the central Sub-Sahara for central and eastern migrants, while turtle doves using the western flyway originated primarily in the western Sub-Sahara, highlighting the importance of both regions for the future conservation of turtle doves from European breeding populations. The establishment of migratory connectivity of populations requires sampling from birds from the European as well as Asian continent; however, we provide important results that can be used to test hypotheses regarding population declines resulting from factors experienced over the full annual cycle for some populations.

Soil δ13C and δ15N baselines clarify biogeographic heterogeneity in isotopic discrimination of European badgers (Meles meles)

Isotopic techniques have been used to study phenomena in the geological, environmental, and ecological sciences. For example, isotopic values of multiple elements elucidate the pathways energy and nutrients take in the environment. Isoscapes interpolate isotopic values across a geographical surface and are used to study environmental processes in space and time. Thus, isoscapes can reveal ecological shifts at local scales, and show distribution thresholds in the wider environment at the macro-scale. This study demonstrates a further application of isoscapes, using soil isoscapes of ¹³C/¹²C and ¹⁵N/¹⁴N as an environmental baseline, to understand variation in trophic ecology across a population of Eurasian badgers (Meles meles) at a regional scale. The use of soil isoscapes reduced error, and elevated the statistical signal, where aggregated badger hairs were used, and where individuals were identified using genetic microarray analysis. Stable isotope values were affected by land-use type, elevation, and meteorology. Badgers in lowland habitats had diets richer in protein and were adversely affected by poor weather conditions in all land classes. It is concluded that soil isoscapes are an effective way of reducing confounding biases in macroscale, isotopic studies. The method elucidated variation in the trophic and spatial ecology of economically important taxa at a landscape level. These results have implications for the management of badgers and other carnivores with omnivorous tendencies in heterogeneous landscapes.

The Use of Intrinsic Markers for Studying the Migratory Movements of Bats

Mortality of migratory bat species at wind energy facilities is a well-documented phenomenon, and mitigation and management are partially constrained by the current limited knowledge of bat migratory movements. Analyses of biochemical signatures in bat tissues ("intrinsic markers") can provide information about the migratory origins of individual bats. Many tissue samples for intrinsic marker analysis may be collected from living and dead bats, including carcasses collected at wind energy facilities. In this paper, we review the full suite of available intrinsic marker analysis techniques that may be used to study bat migration, with the goal of summarizing the current literature and highlighting knowledge gaps and opportunities. We discuss applications of the stable isotopes of hydrogen, oxygen, nitrogen, carbon, sulfur; radiogenic strontium isotopes; trace elements and contaminants; and the combination of these markers with each other and with other extrinsic markers. We further discuss the tissue types that may be analyzed for each and provide a synthesis of the generalized workflow required to link bats to origins using intrinsic markers. While stable hydrogen isotope techniques have clearly been the leading approach to infer migratory bat movement patterns across the landscape, here we emphasize a variety of lesser used intrinsic markers (i.e., strontium, trace elements, contaminants) that may address new study areas or answer novel research questions.

Isotope record tracks changes in historical wintering ranges of a passerine in sub-Saharan Africa

Billions of birds migrate from the Palaearctic to sub-Saharan Africa, yet we are unaware about where exactly they stay over winter and how consistent they have been using these wintering areas over historical times. Here, we inferred the historical wintering areas of Eurasian Golden Orioles (Oriolus oriolus) from stable isotope ratios of feathers. Over the past 200 years, Golden Orioles used two major wintering grounds. Between 1895 and 1971, the relative use of these areas depended on local rainfall intensities. Golden Orioles may depend strongly on humid wintering areas in sub-Saharan Africa, which may put this species at stake when the global climate continues to change.

Autumn migration direction of juvenile willow warblers (Phylloscopus t. trochilus and P. t. acredula) and their hybrids assessed by qPCR SNP genotyping

BACKGROUNDS

Geographic regions, where two closely related taxa with different migration routes come into contact, are known as migratory divides. Hybrids originating from migratory divides are hypothesized to migrate intermediately relative to the parental populations. Few studies have tested this hypothesis in wild birds, and only in hybrids that have completed the migration back to the breeding grounds. Here, we make use of the well-established migration routes of willow warblers (Phylloscopus trochilus), for which the subspecies trochilus and acredula have migration-associated genetic markers on chromosomes 1 and 5. The genetic approach enabled us to analyze the geographic distribution of juveniles during their first autumn migration, predicting that hybrids should be more frequent in the central flyway over Italy than along the typical SW routes of trochilus and SE routes of acredula.

METHODS

Blood and feather samples were collected from wintering birds in Africa (n = 69), and from juveniles during autumn migration in Portugal (n = 33), Italy (n = 38) and Bulgaria (n = 32). Genotyping was carried out by qPCR SNP assays, on one SNP each on chromosome 1 (SNP 65) and chromosome 5 (SNP 285). Both these SNPs have alternative alleles that are highly fixed (> 97%) in each of the subspecies.

RESULTS

The observed combined genotypes of the two SNPs were associated with the known migration routes and wintering distributions of trochilus and acredula, respectively. We found hybrids (HH) among the juveniles in Italy (5/38) and in Portugal (2/33). The proportion of hybrids in Italy was significantly higher than expected from a background rate of hybrid genotypes (1.5%) in allopatric populations of the subspecies.

CONCLUSIONS

Our genetic approach to assign individuals to subspecies and hybrids allowed us to investigate migration direction in juvenile birds on their first migration, which should better reflect the innate migratory direction than studies restricted to successful migrants. The excess of hybrids in Italy, suggests that they employ an intermediate route relative to the parental populations. Our qPCR SNP genotyping method is efficient for processing large sample sizes, and will therefore be useful in migration research of species with known population genetic structure.

From stable isotope ecology to forensic isotope ecology - Isotopes' tales

Stable isotope ecology and forensic isotope ecology are not only linked by name. More often than not, knowledge and insights gained through the former serve as a springboard for application focused work of the latter. This review aims to offer a glimpse into the fascinating world of both though with more emphasis on forensic isotope ecology. To this end a selection of past and recent published work is presented and discussed to highlight both potential and limitations of isotopic analytical approaches to the detection of illegal trade in plants and animals.

Interspecific transfer of parasites following a range-shift in Ficedula flycatchers

Human-induced climate change is expected to cause major biotic changes in species distributions and thereby including escalation of novel host-parasite associations. Closely related host species that come into secondary contact are especially likely to exchange parasites and pathogens. Both the Enemy Release Hypothesis (where invading hosts escape their original parasites) and the Novel Weapon Hypothesis (where invading hosts bring new parasites that have detrimental effects on native hosts) predict that the local host will be most likely to experience a disadvantage. However, few studies evaluate the occurrence of interspecific parasite transfer by performing wide-scale geographic sampling of pathogen lineages, both within and far from host contact zones. In this study, we investigate how haemosporidian (avian malaria) prevalence and lineage diversity vary in two, closely related species of passerine birds; the pied flycatcher Ficedula hypoleuca and the collared flycatcher F. albicollis in both allopatry and sympatry. We find that host species is generally a better predictor of parasite diversity than location, but both prevalence and diversity of parasites vary widely among populations of the same bird species. We also find a limited and unidirectional transfer of parasites from pied flycatchers to collared flycatchers in a recent contact zone. This study therefore rejects both the Enemy Release Hypothesis and the Novel Weapon Hypothesis and highlights the complexity and importance of studying host-parasite relationships in an era of global climate change and species range shifts.

Matching geographical assignment by stable isotopes with African non-breeding sites of barn swallows Hirundo rustica tracked by geolocation

Knowledge on whereabouts within the annual cycle of migratory species is prerequisite for many aspects in ecology and biological conservation. Spatial assignments of stable isotopes archived in tissues allows for later inference on sites where the specific tissue had been grown. It has been rarely tested whether spatial assignments match directly tracked non-breeding residences, especially for migratory songbirds. We here compare assignments of stable isotopes from feathers of Palaearctic Barn swallows Hirundo rustica with their African non-breeding residence sites tracked by geolocation.Assignments based on δ²H, δ¹³C and δ¹⁵N isotope compositions delineate three main non-breeding regions: a main cluster in central Africa, a second in West Africa, and the third cluster in Northern Africa. Using δ¹³C, δ¹⁵N only, non-breeding sites ranged from clusters in West/Southwest Africa to South East Africa with a centre in Central Africa. The non-breeding areas (50% and 75% Kernel density estimates, KDE) of the birds tracked by geolocation stretched from West Africa via central Africa to southern Africa. We found little overlap of 0.3% (assuming a 1:1 odds ratio) to 1.4% (3:1 odds ratio) in the three element assignments and KDEs for only 2 and 13 individuals out of 32 birds. Assignment maps for two elements (δ¹³C, δ¹⁵N) and KDEs showed higher consistencies with an overlap of 3.6 and 8.5% for 12 and 18 birds. We argue that the low matching between stable isotope assignments and non-breeding sites in our study arise from insufficient baseline data for Africa (concerning both isoscapes and specific discrimination functions). However, other factors like aerial foraging habit of the species, and a potential mismatch of non-breeding site location and the spatial origin of aerial plankton might further hamper accurate assignments. Finally we call for concerted analyses of tissues i.e. feathers and claws of birds which are grown at known sites across the continent and from species with various ecological requirements (diverse habitats, foraging behaviours, and diet compositions) to establish isoscapes for general applicability.

Investigating human geographic origins using dual-isotope (87Sr/86Sr, δ18O) assignment approaches

Substantial progress in the application of multiple isotope analyses has greatly improved the ability to identify nonlocal individuals amongst archaeological populations over the past decades. More recently the development of large scale models of spatial isotopic variation (isoscapes) has contributed to improved geographic assignments of human and animal origins. Persistent challenges remain, however, in the accurate identification of individual geographic origins from skeletal isotope data in studies of human (and animal) migration and provenance. In an attempt to develop and test more standardized and quantitative approaches to geographic assignment of individual origins using isotopic data two methods, combining ⁸⁷Sr/⁸⁶Sr and δ¹⁸O isoscapes, are examined for the Circum-Caribbean region: 1) an Interval approach using a defined range of fixed isotopic variation per location; and 2) a Likelihood assignment approach using univariate and bivariate probability density functions. These two methods are tested with enamel isotope data from a modern sample of known origin from Caracas, Venezuela and further explored with two archaeological samples of unknown origin recovered from Cuba and Trinidad. The results emphasize both the potential and limitation of the different approaches. Validation tests on the known origin sample exclude most areas of the Circum-Caribbean region and correctly highlight Caracas as a possible place of origin with both approaches. The positive validation results clearly demonstrate the overall efficacy of a dual-isotope approach to geoprovenance. The accuracy and precision of geographic assignments may be further improved by better understanding of the relationships between environmental and biological isotope variation; continued development and refinement of relevant isoscapes; and the eventual incorporation of a broader array of isotope proxy data.

Multi-Isotopic (δ2H, δ13C, δ15N) Tracing of Molt Origin for Red-Winged Blackbirds Associated with Agro-Ecosystems

We analyzed stable-hydrogen (δ2H), carbon (δ13C) and nitrogen (δ 15N) isotope ratios in feathers to better understand the molt origin and food habits of Red-winged Blackbirds (Agelaius phoeniceus) near sunflower production in the Upper Midwest and rice production in the Mid-South of the United States. Outer primary feathers were used from 661 after-second-year (ASY) male blackbirds collected in Minnesota, Montana, North Dakota and South Dakota (spring collection), and Arkansas, Louisiana, Mississippi, Missouri and Texas (winter collection). The best-fit model indicated that the combination of feather δ2H, δ13C and δ15N best predicted the state of sample collections and thus supported the use of this approach for tracing molt origins in Red-winged Blackbirds. When considering only birds collected in spring, 56% of birds were classified to their collection state on the basis of δ2H and δ13C alone. We then developed feather isoscapes for δ13C based upon these data and for δ2H based upon continental patterns of δ2H in precipitation. We used 81 birds collected at the ten independent sites for model validation. The spatially-explicit assignment of these 81 birds to the δ2H isoscape resulted in relatively high rates (~77%) of accurate assignment to collection states. We also modeled the spatial extent of C3 (e.g. rice, sunflower) and C4 (corn, millet, sorghum) agricultural crops grown throughout the Upper Midwest and Mid-South United States to predict the relative use of C3- versus C4-based foodwebs among sampled blackbirds. Estimates of C3 inputs to diet ranged from 50% in Arkansas to 27% in Minnesota. As a novel contribution to blackbird conservation and management, we demonstrate how such feather isoscapes can be used to predict the molt origin and interstate movements of migratory blackbirds for subsequent investigations of breeding biology (e.g. sex-specific philopatry), agricultural depredation, feeding ecology, physiology of migration and sensitivity to environmental change.