Non-invasive methods to measure androgen metabolites in excrements of European stonechats, Saxicola torquata rubicola

Validation of Fecal Glucocorticoid Metabolites as Non-Invasive Markers for Monitoring Stress in Common Buzzards (Buteo buteo)

For wild animals, being in captivity in wildlife centers can cause considerable stress. Therefore, it is necessary to establish and validate non-invasive tools to measure chronic stress during rehabilitation. Eight Common Buzzards which lived in permanent husbandry were placed individually into prepared aviaries and their feces were collected before, during and after a stress event for biological validation over a period of seven days. The extracted fecal glucocorticoid metabolites (fGCMs) were analyzed with three different enzyme immune assays (EIA) to find the most suitable one. Additionally, we aimed to investigate the stability of fGCM levels after defecation because further metabolization by bacterial enzymes can lead to changed results. The Cortisone-EIA performed best in males and females and showed that the stress event led to an fGCM increase of 629% (557% in females and 702% in males) in relation to basal values. We found no significant differences between the sexes, but observed significant differences between different times of day. FGCM concentration significantly changed after eight hours at room temperature. Our study successfully validated the non-invasive measurement of fGCM as a stress indicator in Common Buzzards and could therefore lay the foundation for future studies providing new insights for animal welfare research in Buzzards.

Validation of enzyme immunoassays for quantifying sex steroid hormones in tropical screech owls (Megascops choliba)

Androgens and estrogens are steroid hormones that regulate reproductive processes in both males and females. Monitoring plasma levels of these steroids or their metabolites present in feces, offers diagnostic support for assessing the reproductive status of animals. Immunoassays are commonly used methods for quantifying these hormones, but their protocols require species-specific validation to ensure reliability. The objective of this study was to perform analytically and biologically validation of enzyme immunoassay (EIA) kits for measuring testosterone (T), estradiol (E2), faecal androgen metabolites (fAM), and faecal estrogenic metabolites (fEM) in the tropical screech owl (Megascops choliba). Serum and fecal samples were collected from six adult females and six males both before and during breeding season, with males' gonadal activity assessed using electroejaculation (EE). The parallelism test confirmed the immunogenic similarity of the antigens in the estradiol and testosterone standards and the antigens in the serum samples and fecal extracts of M. choliba. Additionally, the EIA kits displayed nearly 100% recovery rates, and showed coefficients of variation ranging from 8% to 14% at the intra-assay level and from 10% to 16% at the inter-assay level, underscoring result reliability and consistency. In males, the highest serum T and fAM levels were recorded concurrently with the presence of spermatozoa in samples collected via EE. Although females did not exhibit oviposition events, significantly higher E2 and fEM levels were observed in August compared to May, suggesting potential seasonal variations in estrogenic hormone production. Fecal androgen and estrogen levels were significantly different between sexes in August, with males having higher fAM and females having higher fEM levels. Overall, the immunoassays validated in this study were found to be efficient in diagnosing reproductive activity in owls.

Biocompatible polymeric microparticles serve as novel and reliable vehicles for exogenous hormone manipulations in passerines

The administration of exogenous hormones emerged as an essential tool for field studies in endocrinology. However, working with wild animals remains challenging, because under field conditions not every available method meets the necessary requirements. Achieving a sustained elevation in hormone levels, while simultaneously minimising handling time and invasiveness of the procedure is a difficult task in field endocrinology. Facing this challenge, we have investigated the suitability of biocompatible polymeric microparticles, a novel method for drug-administration, as a tool to manipulate hormones in small songbirds. We chose the insulin-like growth factor-1 (IGF-1) as target hormone, because it receives great interest from the research community due to its important role in shaping life-history traits. Moreover, its short half-life and hydrophilic properties imply a major challenge in finding a suitable method to achieve a sustained, systemic long-term release. To study the release kinetics, we injected either IGF-1 loaded polylactic-co-glycolic acid (PLGA) microparticles or dispersion medium (control group) in the skin pocket of the interscapular region of captive bearded reedlings (Panurus biarmicus). We collected blood samples for 7 consecutive days plus an additional sampling period after two weeks and complemented these with an in vitro experiment. Our results show that in vitro, PLGA microparticles allowed a stable IGF-1 release for more than 15 days, following a burst release at the beginning of the measurement. In vivo, the initial burst was followed by a drop to still elevated levels in circulating IGF-1 until the effect vanished by 16 days post-treatment. This study is the first to describe the use of PLGA-microparticles as a novel tool for exogenous hormone administration in a small passerine. We suggest that this method is highly suitable to achieve the systemic long-term release of hydrophilic hormones with short half-life and reduces overall handling time, as it requires only one subcutaneous injection.

The Gene Expression Profile of the Song Control Nucleus HVC Shows Sex Specificity, Hormone Responsiveness, and Species Specificity Among Songbirds

Singing occurs in songbirds of both sexes, but some species show typical degrees of sex-specific performance. We studied the transcriptional sex differences in the HVC, a brain nucleus critical for song pattern generation, of the forest weaver (Ploceus bicolor), the blue-capped cordon-bleu (Uraeginthus cyanocephalus), and the canary (Serinus canaria), which are species that show low, medium, and high levels of sex-specific singing, respectively. We observed persistent sex differences in gene expression levels regardless of the species-specific sexual singing phenotypes. We further studied the HVC transcriptomes of defined phenotypes of canary, known for its testosterone-sensitive seasonal singing. By studying both sexes of canaries during both breeding and non-breeding seasons, non-breeding canaries treated with testosterone, and spontaneously singing females, we found that the circulating androgen levels and sex were the predominant variables associated with the variations in the HVC transcriptomes. The comparison of natural singing with testosterone-induced singing in canaries of the same sex revealed considerable differences in the HVC transcriptomes. Strong transcriptional changes in the HVC were detected during the transition from non-singing to singing in canaries of both sexes. Although the sex-specific genes of singing females shared little resemblance with those of males, our analysis showed potential functional convergences. Thus, male and female songbirds achieve comparable singing behaviours with sex-specific transcriptomes.

Habitat urbanization and stress response are primary predictors of personality variation in northern cardinals (Cardinalis cardinalis)

Behavioral traits that vary consistently among individuals across different contexts are often termed as ‘personality traits,’ while the correlated suite formed by those traits is called a ‘behavioral syndrome’. Both personality trait and behavioral syndrome are potentially responsive to animal ‘states’, defined as strategically relevant individual features affecting the cost-and-benefit trade-offs of behavioral actions. Both extrinsic ‘states’ (e.g. urban versus rural habitats), and intrinsic ‘states’ (e.g. sex), may shape among-individual variation in personality traits, as well as behavioral syndromes. Here, we used northern cardinals sampled from four locations to examine the effect of habitat type (urban versus rural, an extrinsic state), stress hormone corticosterone (CORT) parameters, body weight and sex (intrinsic states) on personality traits and behavioral syndrome variation. We used behavioral trials to measure five personality traits. Using principal component analysis to quantify personality traits first, followed by general linear mixed models, we found that habitat type, CORT at capture and 2-day CORT response affected some personality traits, while body weight and sex did not. Cardinals inhabiting more urbanized areas had lower CORT metabolite levels at capture and were more neophilic, less neophobic and also less aggressive than their rural conspecifics. Using structural equation modeling to construct behavioral syndromes formed by our selected personality traits, we found that urban and rural cardinals varied in the models representing syndrome structure. When utilizing the shared syndrome structural model to examine the effects of states, habitat type and 2-day CORT response appear to affect syndrome variation in a coordinated, not hierarchical, manner.

Characteristics of song, brain-anatomy and blood androgen levels in spontaneously singing female canaries

Females of many northern temperate songbird species sing sporadically. However, detailed descriptions of female song are rare. Here we report a detailed analysis of song in a small number of spontaneously-singing female domesticated canaries (Serinus canaria) under non-breeding, laboratory conditions in a large population of domesticated birds. In-depth analysis showed that these females sang rarely, and the spontaneous songs varied between and within birds over time. Furthermore, spontaneous female songs were distinct from songs of testosterone-induced singing female canaries and from songs of male canaries in both temporal and spectral features. Singing females had significantly elevated plasma androgen levels and a larger size of the major song controlling brain nuclei HVC (used as a proper name) and the robust nucleus of the arcopallium (RA) than non-singing females housed under similar conditions. The sporadically observed production of song and accompanying differences in brain anatomy in female canaries may thus depend on minute intraspecific differences in androgen levels.

Measuring fecal testosterone in females and fecal estrogens in males: comparison of RIA and LC/MS/MS methods for wild baboons (Papio cynocephalus)

The development of non-invasive methods, particularly fecal determination, has made possible the assessment of hormone concentrations in wild animal populations. However, measuring fecal metabolites needs careful validation for each species and for each sex. We investigated whether radioimmunoassays (RIAs) previously used to measure fecal testosterone (fT) in male baboons and fecal estrogens (fE) in female baboons were well suited to measure these hormones in the opposite sex. We compared fE and fT concentrations determined by RIA to those measured by liquid chromatography combined with triple quadropole mass spectrometry (LC/MS/MS), a highly specific method. Additionally, we conducted a biological validation to assure that the measurements of fecal concentrations reflected physiological levels of the hormone of interest. Several tests produced expected results that led us to conclude that our RIAs can reliably measure fT and fE in both sexes, and that within-sex comparisons of these measures are valid: (i) fTRIA were significantly correlated to fTLC/MS/MS for both sexes; (ii) fTRIA were higher in adult than in immature males; (iii) fTRIA were higher in pregnant than non-pregnant females; (iv) fERIA were correlated with 17β-estradiol (fE2) and with estrone (fE1) determined by LC/MS/MS in pregnant females; (v) fERIA were significantly correlated with fE2 in non-pregnant females and nearly significantly correlated in males; (vi) fERIA were higher in adult males than in immature males. fERIA were higher in females than in males, as predicted, but unexpectedly, fTRIA were higher in females than in males, suggesting a difference in steroid metabolism in the two sexes; consequently, we conclude that while within-sex comparisons are valid, fTRIA should not be used for intersexual comparisons. Our results should open the field to important additional studies, as to date the roles of testosterone in females and estrogens in males have been little investigated.

Longitudinal monitoring of sex steroid hormones in excrement of spectacled eiders (Somateria fischeri)

From the 1970s to the 1990s, the breeding population of spectacled eiders (Somateria fischeri) in western Alaska declined by 96%, which led to the listing of this species as threatened under the Endangered Species Act in 1993. Since then, the population has stabilized, but has not recovered to pre-decline numbers. While little is known about reproductive endocrinology in spectacled eiders, in other avian species, estrogen and testosterone are known to initiate and modulate various reproductive processes including yolk protein synthesis, reproductive behaviors and secondary sex characteristics. Measurement of the metabolites of estrogen and testosterone (EM and TM, respectively) in excrement reflect circulating hormone concentrations and provide a non-invasive method to monitor reproductive physiology. We measured concentrations of excreted EM in captive females and TM in males to (1) determine the efficacy of commercially available radioimmunoassay kits to detect EM and TM, (2) describe annual profiles of EM and TM concentrations, and (3) define the reproductive season of captive spectacled eiders using endocrine status. Excrement samples were collected from captive female and male spectacled eiders three times per week throughout 1 year. Female EM and male TM levels were quantified using radioimmunoassay. Mean female EM profile exhibited values exceeding the threshold for "peak" values (EM>193.3 ng/g) from mid-February to early July, and again in September. Additionally, the highest average concentrations of EM were seen in March, May and September. Elevated TM concentrations occurred in mid March, mid May and late June. These data suggest that levels of excreted sex steroids reflect patterns predicted by breeding landmarks in the annual cycle and will assist in field monitoring and captive breeding programs for spectacled eiders.

Androgen and androgen metabolite levels in serum and urine of East African chimpanzees (Pan troglodytes schweinfurthii): comparison of EIA and LC-MS analyses

The primary male androgen testosterone (T) is often used as an endocrinological marker to investigate androgen-behaviour interactions in males. In chimpanzees and bonobos, studies investigating the relationship between T levels and dominance rank or aggressive behaviour have revealed contradictory results. The immunoassays used in these studies were originally developed for the measurement of steroids in serum. Their application to non-invasively collected samples, however, can lead to methodological problems due to cross-reacting metabolites, which might occur in urine or faeces but not in blood. The overall aim of this study, therefore, is to clarify whether a T enzyme immunoassay (EIA) is an applicable method to monitor testicular function in adult male chimpanzees. To estimate the impact of cross-reacting androgens on the used T EIA, we compared the results of an EIA measurement with a set of androgen metabolite levels measured by LC-MS. In urine from male chimpanzees, cross-reactivities appear to exist mainly with T and its exclusive metabolites, 5α-dihydrotestosterone (5α-DHT) and 5α-androstanediol (androstanediol). Both urinary and serum T levels of male chimpanzees were significantly higher than female T levels when measured with the T EIA, indicating a reliable measurement of testicular androgens and their exclusive metabolites with the used EIA. In urine from female chimpanzees, the comparison between LC-MS and T EIA results indicated a higher impact of cross-reactions with adrenal androgen metabolites. Therefore, the investigation of urinary T levels in female chimpanzees with a T EIA seems to be problematic. Overall our results show that a T EIA can be a reliable method to monitor testicular function in male chimpanzee urine and that LC-MS is a valuable tool for the validation of immunoassays.

Sexually selected male plumage color is testosterone dependent in a tropical passerine bird, the red-backed fairy-wren (Malurus melanocephalus)

Background

Sexual signals, such as bright plumage coloration in passerine birds, reflect individual quality, and testosterone (T) may play a critical role in maintaining signal honesty. Manipulations of T during molt have yielded mixed effects on passerine plumage color, in most cases delaying molt or leading to production of drab plumage. However, the majority of these studies have been conducted on species that undergo a post-nuptial molt when T is low; the role of T in species that acquire breeding plumage during a pre-nuptial molt remains largely unexplored.

Methodology/Principal Findings

We experimentally tested the effects of increased T on plumage color in second-year male red-backed fairy-wrens (Malurus melanocephalus), a species in which after-second-year males undergo a pre-nuptial molt into red/black (carotenoid and melanin-based) plumage and second-year males either assume red/black or brown breeding plumage. T treatment stimulated a rapid and early onset pre-nuptial molt and resulted in red/black plumage acquisition, bill darkening, and growth of the sperm storage organ, but had no effect on body condition or corticosterone concentrations. Control males molted later and assumed brown plumage. T treated males produced feathers with similar but not identical reflectance parameters to those of unmanipulated after-second-year red/black males; while reflectance spectra of red back and black crown feathers were similar, black breast feathers differed in UV chroma, hue and brightness, indicating a potentially age and plumage patch-dependent response to T for melanin- vs. carotenoid-pigmentation.

Conclusions/Significance

We show that testosterone is the primary mechanism functioning during the pre-nuptial molt to regulate intrasexually variable plumage color and breeding phenotype in male red-backed fairy-wrens. Our results suggest that the effects of T on plumage coloration may vary with timing of molt (pre- vs. post-nuptial), and that the role of T in mediating plumage signal production may differ across age classes, plumage patches, and between pigment-types.

Seasonal and diel variation of hormone metabolites in European stonechats: on the importance of high signal-to-noise ratios in noninvasive hormone studies

Most vertebrates living in seasonal environments show seasonal reproductive cycles and diel rhythms. The rhythmicity in behavior and morphology is accompanied by diel and seasonal patterns of hormone secretions. In small animals, the investigation of diel patterns of hormones has been hampered because repeated blood sampling is difficult and may influence subsequent measurements. A possibility to avoid these caveats is to investigate excreted hormone metabolites instead. Here, we describe the diel excretion patterns of testosterone and corticosterone metabolites in a small captive songbird during 4 seasons: winter, early spring (Zugunruhe), summer, and autumn molt. Our approach is quite unique, because the diel patterns of steroids have rarely--if at all--been investigated in the same individuals within several seasons. Small birds should be ideal to investigate diel patterns of hormone metabolites, because they defecate frequently enough to establish a diel profile. However, concentration measurements of hormone metabolites rely on the assumptions that hormone metabolites are placed into droppings of similar mass (the "dropping amount assumption") and are excreted in constant time intervals (the "constant interval assumption"). These assumptions were clearly violated in our study, as the dropping mass per time interval and the defecation intervals varied depending on the time of day and season. We thus used the rate of hormone metabolite excretion as an alternative measure to concentration. Both testosterone and corticosterone metabolites showed diel and seasonal rhythmicity. Furthermore, the diel pattern varied depending on season. Concentration and rate measurements gave similar results when the differences between hormone metabolite levels were large-for example, when testosterone metabolites were compared across seasons. When the differences were more subtle, though, the 2 measures did not always correspond well, indicating that the violation of the 2 basic assumptions affected the comparability of concentration measurements. We conclude that diel and seasonal comparisons of hormone metabolites potentially give biologically meaningful results, especially when rates instead of concentrations are measured. However, such studies require awareness of the limitations and pitfalls of noninvasive hormone measurements, a carefully designed experiment, and very cautious interpretation of the data.

Enhanced testosterone levels affect singing motivation but not song structure and amplitude in Bengalese finches

Song is a fundamental component of territory defense and mate attraction in birds, and androgens (like testosterone) are known to play a key role in controlling it. However, little is known about how differences in testosterone levels between males translate into inter-individual song variation. Indeed, testosterone could affect both the motivation to sing and the structure of song itself. Here, we tested whether experimentally elevated testosterone levels in adult Bengalese finches (Lonchura striata var. domestica), an oscine bird species, have an activational effect on 1) song performance, and 2) song structure. Our results show that testosterone-treated males, in contrast to sham-control males, sang more when confronted with a female. Other performance-related traits, however, such as latency to sing and song amplitude, were not affected. Testosterone-treated males also showed no differences in our two measures of song structure: fundamental element frequency and mean song frequency. Because song structure is known to be organizationally affected by testosterone, our results, synthesized together with findings from the current literature, suggest that in oscine birds, song contains multiple messages about the signaler's hormonal status. First, song performance may reflect current hormonal condition, and second, song structure may reflect the past hormonal state.

Toward a mouse neuroethology in the laboratory environment

In this report we demonstrate that differences in cage type brought unexpected effects on aggressive behavior and neuroanatomical features of the mouse olfactory bulb. A careful characterization of two cage types, including a comparison of the auditory and temperature environments, coupled with a demonstration that naris occlusion abolishes the neuroanatomical changes, lead us to conclude that a likely important factor mediating the phenotypic changes we find is the olfactory environment of the two cages. We infer that seemingly innocuous changes in cage environment can affect sensory input relevant to mice and elicit profound effects on neural output. Study of the neural mechanisms underlying animal behavior in the laboratory environment should be broadened to include neuroethological approaches to examine how the laboratory environment (beyond animal well-being and enrichment) influences neural systems and behavior.

A safer method for studying hormone metabolism in an Asian elephant (Elephas maximus): accelerator mass spectrometry

Noninvasive hormone assays provide a way to determine an animal's health or reproductive status without the need for physical or chemical restraint, both of which create unnecessary stress for the animal, and can potentially alter the hormones being measured. Because hormone metabolism is highly species-specific, each assay must be validated for use in the species of interest. Validation of noninvasive steroid hormone assays has traditionally required the administration of relatively high doses of radiolabelled compounds (100 µCi or more of (14)C labeled hormone) to permit subsequent detection of the excreted metabolites in the urine and feces. Accelerator mass spectrometry (AMS) is sensitive to extremely low levels of rare isotopes such as (14)C, and provides a way to validate hormone assays using much lower levels of radioactivity than those traditionally employed. A captive Asian bull elephant was given 1 µCi of (14)C-testosterone intravenously, and an opportunistic urine sample was collected 2 hr after the injection. The sample was separated by HPLC and the (14)C in the fractions was detected by AMS to characterize the metabolites present in the urine. A previously established HPLC protocol was used, which permitted the identification of fractions into which testosterone sulfate, testosterone glucuronide, and the parent compound testosterone elute. Results from this study indicate that the majority of testosterone excreted in the urine of the Asian bull elephant is in the form of testosterone sulfate. A small amount of testosterone glucuronide is also excreted, but there is no parent compound present in the urine at all. These results underscore the need for enzymatic hydrolysis to prepare urine samples for hormone assay measurement. Furthermore, they highlight the importance of proper hormone assay validation in order to ensure accurate measurement of the desired hormone. Although this study demonstrated the utility of AMS for safer validation of noninvasive hormone assays in nondomestic species, this methodology could also be applied to studies of nutrient metabolism and drug pharmakokinetics, both areas in great need of further study in wildlife species.

Does testosterone mediate the trade-off between nestling begging and growth in the canary (Serinus canaria)?

Nestling birds solicit food from their parents with vigorous begging displays, involving posturing, jostling and calling. In some species, such as canaries, begging is especially costly because it causes a trade off against nestling growth. Fitness costs of begging like this are predicted by evolutionary theory because they function to resolve conflicts of interest within the family over the provision of parental investment. However, the mechanism that links these costs with nestling behaviour remains unclear. In the present study, we determine if the relationships between nestling androgen levels, nestling begging intensities and nestling growth rates are consistent with the hypothesis that testosterone is responsible for the trade-off between begging and growth. We test this idea with a correlational study, using fecal androgens as a non-invasive method for assaying nestling androgen levels. Our results show that fecal androgen levels are positively correlated with nestling begging intensity, and reveal marked family differences in each trait. Furthermore, changes in fecal androgen levels between 5 and 8 days after hatching are positively associated with changes in nestling begging intensity, and negatively associated with nestling growth during this time. Although these correlational results support our predictions, we suggest that that experimental manipulations are now required to test the direct or indirect role of testosterone in mediating the trade-off between begging and growth.

Fecal steroid monitoring for assessing gonadal and adrenal activity in the golden eagle and peregrine falcon

We examined the efficacy of noninvasive monitoring of endocrine function via fecal steroid immunoassays in the golden eagle and peregrine falcon. High-pressure liquid chromatography analyses of fecal glucocorticoid metabolites (fGCM) revealed that minor percentages of immunoreactive fGCM co-eluted with [(3)H]corticosterone in both sexes of the eagle (2.5-2.7%) and falcon (7.5-11.9%). In contrast, most fecal estrogen metabolites in eagle and falcon females co-eluted with radiolabeled estradiol-17beta ([(3)H]; 57.6, 64.6%, respectively) or estrone ([(3)H]; 26.9, 4.1%, respectively). Most fecal progestin metabolite immunoreactivity in the female eagle (24.8%) and falcon (21.7%) co-eluted with progesterone ([(14)C]). Most fecal androgen metabolite immunoreactivity in eagle (55.8%) and falcon (63.7%) males co-eluted with testosterone ([(14)C]). Exogenous adrenocorticotropin hormone induced increased fGCM excretion above pre-treatment in both species, but only significantly (P < 0.05) in the eagle. Both species showed increased fGCM after saline administration, suggesting the detection of 'handling stress.' Both species exhibited enterohepatic and renal recirculation of administered steroids as demonstrated by biphasic and triphasic excretion patterns. Thus, noninvasive fecal hormone monitoring is a valid and promising tool for assessing gonadal and adrenal status in rare and threatened birds-of-prey.

Low ambient temperature increases food intake and dropping production, leading to incorrect estimates of hormone metabolite concentrations in European stonechats

Non-invasive methods to measure steroid hormone metabolites in bird droppings or mammalian feces have become very popular. However, the accuracy of these measurements may be affected by many factors. Here, we use the stonechat (Saxicola torquata) as a passerine bird model to test whether differences in ambient temperature affect food intake and dropping production and whether these changes lead to measurement artefacts in hormone metabolite concentrations. In addition, we tested for diurnal patterns in hormone metabolites. We held European stonechats in climate chambers and subjected them to two different long-term ambient temperature regimes, +5 degrees C and +22 degrees C. As expected, food intake and dropping production was higher at +5 degrees C than at +22 degrees C. Plasma concentrations of corticosterone and testosterone did not differ between different ambient temperature regimes. However, corticosterone and testosterone metabolite concentrations (in ng/g) were significantly lower at +5 degrees C than at +22 degrees C. When we measured the rate of hormone metabolite excretion (in picogram per hour) instead of the concentration, there was no difference between treatment groups. Thus, the measurement of hormone metabolite concentrations can be flawed because, depending on the treatment, similar amounts of hormone metabolites can be excreted into very different amounts of droppings. In conclusion, hormone metabolite concentration measurements are sensitive to changes in ambient temperature and probably any other factor that alters metabolic rates. Any study involving systematic changes in metabolism--i.e., during molt, migration, hibernation, egg production, or seasonal comparisons--needs to take these caveats into account.

Fecal corticosterone, body mass, and caching rates of Carolina chickadees (Poecile carolinensis) from disturbed and undisturbed sites

We tested for hormonal and behavioral differences between Carolina chickadees (Poecile carolinensis) taken from a disturbed (recently logged) forest, an undisturbed forest, or a residential site. We measured fecal corticosterone and body mass levels in the field, and fecal corticosterone, body mass, and caching behavior in an aviary experiment. In the field, birds from the disturbed forest exhibited significantly higher fecal corticosterone levels than birds from either the undisturbed forest or from the residential site. Birds from the disturbed forest also exhibited lower body mass than those from the undisturbed forest but higher body mass than those from the residential site. Our aviary results suggest that these physiological differences between field sites are the result of short-term responses to ecological factors: neither body mass nor fecal corticosterone levels varied between birds captured at different sites. Aviary sample sizes were sufficient to detect seasonal variation in fecal corticosterone (lowest in summer), body mass (highest in spring), and rate of gain in body mass (highest in winter). Under "closed-economy" aviary conditions (all food available from a feeder in the aviary), there were no site differences in the percent of seeds taken from the feeder that were cached. However, under "open-economy" conditions (food occasionally available ad libitum), significantly fewer seeds were cached by birds from the disturbed forest compared to the undisturbed or residential sites. On average, there was only a two-fold difference in population levels of fecal corticosterone. This difference is about the same as an increase in fecal corticosterone induced by a 2-h increase in food deprivation and cannot be considered to be an acute stress response to disturbance.

Nestling testosterone is associated with begging behaviour and fledging success in the pied flycatcher, Ficedula hypoleuca

Animal signals are hypothesized to be costly in order to honestly reflect individual quality. Offspring solicitation signals given by nestling birds are thought to have evolved to advertise either need or individual quality. We tested the potential role of testosterone (T) in controlling the intensity of these signals by measuring begging behaviour as: (i) duration of the begging display and (ii) maximum height of the begging stretch, and by sampling endogenous T levels in nestling blood. We tested nestling pied flycatchers (Ficedula hypoleuca) using well-established experimental paradigm involving transient food deprivation to encourage begging behaviour and then blood-sampled nestlings at the end of these tests for T levels. Our results show that individual nestlings with the most intense begging displays had the highest circulating levels of T immediately after testing. In addition, we found substantial differences between broods in terms of circulating T. Finally, we found evidence that broods with higher levels of T showed increased fledging success, indicating a benefit for increased T production in nestlings. The potential trade-offs involved in T-mediated begging behaviour are discussed.

Synthesis of Measuring Steroid Metabolites in Goose Feces

The reliability of noninvasively measuring steroid hormones from feces in greylag geese (Anser anser) and domestic geese (A. domesticus), both qualitatively and quantitatively, was tested experimentally. Geese are mainly herbivorous birds with a short gut-passage time (2-3 h). Groups of eight outdoor-housed male domestic geese were subjected to two different experiments, injection of either GnRH or ACTH, which were replicated in three different seasons (spring, summer, and fall). GnRH stimulation resulted in significant increases of response fecal testosterone metabolites (TM; 17beta-OH-androgens) in spring and fall, but not during the summer photorefractoriness. Testosterone response patterns obtained from plasma samples paralleled those from feces; however, no direct correlation between individual immunoreactive plasma and feces contents was observed. To improve the sample handling during extraction and the assay sensitivity, we promote the use of a group-specific antibody against 17-oxoandrogens that does not require deconjugation prior to the analysis. ACTH robustly increased fecal corticosterone in all seasons. The polar nature of glucocorticoids, however, seems to make a distinction between conjugated and nonconjugated types difficult, and the available avian literature on this topic is discussed.

Noninvasive Measures of Reproductive Function and Disturbance in the Barred Owl, Great Horned Owl, and Northern Spotted Owl

There is an urgent need for noninvasive methods to study reproduction and environmental stress in at-risk species such as the northern spotted owl (Strix occidentalis caurina). Two related owl species (barred owl and great horned owl) were used as surrogates to validate hormone assays for fecal metabolites of progesterone, 17beta-estradiol, testosterone, and corticosterone. Infusions of radiolabeled hormones showed that the owls excreted most hormone within 6 h. Feces and urine contained roughly equal amounts of hormone, and most fecal hormone metabolites were quite polar. The testosterone and corticosterone assays in this study bound to the major excreted metabolites of these hormones, but two progesterone assays did not appreciably bind to the major progesterone metabolites. All assays showed excellent parallelism with hydrolyzed and unhydrolyzed samples and with previously dried or undried fecal samples. Thus, samples do not require hydrolysis or prior drying. Samples from a female barred owl had significantly higher fecal estrogen, lower fecal testosterone, and higher fecal estrogen/testosterone ratio than samples from two male barred owls. The fecal estrogen/testosterone ratio was the most accurate predictor of owl gender, particularly if two or more samples are available from the same individual. Fecal corticosterone metabolites also demonstrated considerable utility for wild northern spotted owls. Fecal glucocorticoid levels varied by gender and breeding stage, being highest in male northern spotted owls early in the breeding season and highest in females when nestlings were fledging. Collectively, these studies show that noninvasive fecal hormone measurements show great promise for noninvasive assessment of reproduction and stress in wild owls.

Noninvasive monitoring of hormones in bird droppings: physiological validation, sampling, extraction, sex differences, and the influence of diet on hormone metabolite levels

During the past several years, the noninvasive measurement of steroid metabolites from mammalian feces and bird droppings has become more and more popular. With an increasing acceptance of the method, investigators may become less aware of the need to validate their assays. It is shown why such validations are essential for each new species investigated and various ways to physiologically validate such noninvasive methods are described. Using the European stonechat (Saxicola torquata rubicola) as a model, it is explained why a validated method to measure androgen metabolites in males does not necessarily work in females. In addition the difficulties that may be neglected owing to the superficial ease of sampling and processing of excreta are investigated. Various issues that may arise during sampling, storage, and extraction of excreta are addressed. Finally, results suggesting that experimental manipulations of the diet may affect hormone metabolite levels in European stonechats are presented. So far, only a few studies have investigated the impact of diet on hormone metabolite levels, and these are the first data to report such an impact in birds. More studies are urgently needed to learn more about differences between the sexes, individuals, and populations and the impact of diet and energy metabolism on hormone metabolites.

Sampling effort/frequency necessary to infer individual acute stress responses from fecal analysis in Greylag geese (Anser anser)

Measuring hormone metabolites from excreta is a powerful method to study hormone-behavior relationships. Currently, fecal corticosterone metabolite concentrations are used to estimate individual short-term stress responses. From the free-roaming, semitame flock of greylag geese (Anser anser), as many fecal samples as possible were collected over 3 h following a challenge (social density stress) or in a control situation. This time span corresponds to the gut passage time of geese. It was asked how many samples were necessary to determine differences in excreted corticosterone immunoreactive metabolites (CORTs) between control and social density stress and which parameters (means, maxima, range) reliably showed this difference. A large variation of CORT was found between consecutive samples. Still, means, maxima, and ranges of the samples in a fecal series consistently showed the response to a stressor both within and between individuals. Three samples sufficed if the maximum value of CORT was used, whereas four or more samples were necessary to work with the mean. It was concluded that by increasing the number of fecal samples collected, the course of CORT could be measured more precisely and an individual's acute stress response inferred more reliably.

Excremental androgen metabolite concentrations and gonad sizes in temperate zone vs. tropical Stonechats (Saxicola torquata ssp.)

Many songbirds in the temperate zones have comparatively short breeding seasons and are migratory. This often implies high breeding synchrony and competition for food, space, and mates. Tropical birds, in contrast, tend to be resident and react more flexibly to a more variable onset of environmental conditions conducive for breeding. Therefore, it can be expected that androgen metabolite concentrations in breeding males vary among birds from different latitudes. Studies on tropical birds, however, have revealed inconsistent results suggesting that additional factors not directly related to latitude, modify hormone levels. Furthermore, there is a potential for a phylogenetic bias when comparing birds of different taxonomic groups. In the present study, we compared androgen metabolite concentrations among closely related taxa of hand-raised male stonechats originating from tropical and temperate-zone populations in Kenya (0 degrees latitude), Kazakhstan (52 degrees N), and Ireland (52 degrees N), which differ partly in latitude of their provenance but also in the length of their breeding season (birds from Kazakhstan vs. Ireland). Hand-raised birds were housed in their natural photoperiod under otherwise identical environmental conditions. Androgen levels were determined from excrements to reduce disturbance. All three groups demonstrated a seasonal cycle of androgen metabolite concentrations concomitant with testis growth. Peak androgen metabolite concentrations were significantly lower in Kenyan stonechats compared to Kazakh stonechats. Irish birds had intermediate concentrations. Differences between Kazakh and Kenyan stonechats correlate with latitude, but data from the Irish population suggest the involvement of factors not directly related to latitude.