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.

Aggressiveness predicts dominance rank in greylag geese: mirror tests and agonistic interactions

Individual differences in aggressiveness, if consistent across time and contexts, may contribute to the long-term maintenance of social hierarchies in complex animal societies. Although agonistic interactions have previously been used to calculate individuals' positions within a dominance hierarchy, to date the repeatability of agonistic behaviour has not been tested when calculating social rank. Here, we examined the consistency and social relevance of aggressiveness as a personality trait in a free-flying population of greylag geese (Anser anser). For each individual, we quantified (i) aggressiveness using a standardized mirror stimulation test and (ii) dominance ranking based on the number of agonistic interactions won and lost in a feeding context. We found that individual differences in aggressiveness were significantly repeatable and that individuals' aggressiveness predicted their dominance rank position. The flock showed a robust and intermediately steep dominance hierarchy. Social rank was higher in paired birds, males and older birds, and most agonistic interactions occurred between individuals with moderate rank differences. We suggest that selection favours aggressiveness as a personality trait associated with resource acquisition and social rank, whereby a dominance hierarchy may increase the benefits of group living and reduce costs over conflict within dyads.

Seasonal variation in molecular and physiological stress markers in Asian elephants

Free-living species exhibit seasonal variation in various life history traits, including vital rates such as birth and death patterns. Different physiological mechanisms are thought to underlie the expression of life history traits that contribute to lifetime fitness. However, although the broad impacts of seasonality on life history traits and trade-offs is well established in many systems, the exact physiological mechanisms responsible for driving differences within and between individuals are poorly understood. Among them, molecular and physiological stress pathways, such as stress hypothalamic-pituitary-adrenal axis and oxidative stress, have potential to mediate relationships between individual survival, reproduction and environmental seasonality. Here, we determine how different physiological markers of stress including faecal cortisol metabolites (FCMs), heterophils/lymphocytes (H/L) ratio, two markers indicating oxidative balance including a marker of oxidative damage (reactive oxygen metabolites, ROM) and a marker of antioxidant defences (superoxide dismutase, SOD) and body weight vary in a large semi-captive population of Asian elephants (Elephas maximus) exposed to extreme seasonality (e.g. elevated temperatures). Individuals showed higher FCM levels and H/L ratios during cold season, indicating increased stress, and the lowest FCM levels during monsoon season and H/L ratios during hot and dry season, but we found no pattern in oxidative stress (ROM and SOD) levels. Hot season also associated with a decline in body weight. The present study shows how different physiological parameters (FCM levels and H/L ratio), molecular (oxidative stress) and body condition vary with seasonal changes, and how these parameters might allow individuals to adapt to such variations. Our results on an endangered long-lived species are crucial in indicating the most productive timing for conservation efforts, predicting how individuals cope with environmental changes, and allow for a more accurate representation of how animal physiology operates in nature.

The association of social rank with paternity efficiency in competitive mating flocks of Zi goose ganders (Anser cygnoides L.)

The purpose of this study was to investigate the influence of social rank (SR) on paternity efficiency (PE) in competitive mating flocks of geese. Thirty ganders and 150 geese (Zi geese, Anser cygnoides L.) aged approximately one, were divided into 3 groups. Flock 1 included 10 ganders and 50 female geese, flock 2 included 11 ganders and 55 female geese, and flock 3 included 9 ganders and 45 female geese. The frequency of the agonistic behavioral interactions (ABI) of the ganders and mating activity (MA) were video recorded in each flock. The SR of each gander was determined by the frequency of ABI with a score of 1 to 3 (1 being the dominant and 3 the most subordinate). To clarify the difference between being dominant and submissive, we collapsed rank 2 and rank 3 into a “subordinate” category. In total, 280 eggs were collected, and 219 goslings were hatched. Parent–offspring relationships among 399 individuals from the 2 generations were identified via 20 microsatellite markers, and the PE of each gander was calculated. There was no significant difference in individual body weight and semen quality factor among the different SR groups (dominant and subordinate), and the SR of the ganders was significantly correlated to PE for the 3 flocks. Goslings of high-ranking ganders contributed 48.68% in flock 1, 37.50% in flock 2, and 47.62% in flock 3. Approximately 45% of all goslings were sired by the 7 dominant ganders of the 30 total ganders across the 3 flocks. As SR has been shown to be heritable in geese, the selection of high-ranking ganders might be an effective way to improve reproductive efficiency in commercial geese flocks.

Costs and benefits of social connectivity in juvenile Greylag geese

Living in groups has various advantages and disadvantages for group members. We investigated the fitness consequences of early social connectivity (normalized Freeman degrees based on nearest neighbour data), physiology (levels of excreted corticosterone metabolites assayed from droppings), and agonistic interactions in a group of free-ranging greylag geese (Anser anser). Forty-four greylag geese below 3 years of age were observed in three different seasonal phases: during the re-aggregation of the flock in autumn, at the end of the winter and during the forthcoming breeding season. We show that corticosterone metabolite levels and initiated and received aggression increased with increasing social connectivity. Individuals had higher connectivity scores in the winter flock than during the mating and breeding seasons. One-year old juveniles were more connected than 2- and 3-year old individuals. In addition, we examined the link between social connectivity during early development and reproductive success several years later. We found that birds with greater connectivity early in life attempted to breed at a younger age. Furthermore, successful breeders with higher early connectivity scores had higher numbers of fledged goslings. Our results show that social context in early life stages may have long-term effects on individual fitness.

Parental behaviour and family proximity as key to gosling survival in Greylag Geese (Anser anser)

Reproductive success in monogamous species is generally affected by both behavioural and hormonal fine-tuning between pair partners. Vigilance, defence and brooding of offspring are among the main parental investments, and often the sexes adopt different roles. In the present study, we investigate how sex differences in parental behaviour and family proximity in the socially monogamous Greylag Goose (Anser anser) affect gosling survival. During the reproductive season in spring 2013, we recorded the behaviour of 18 pairs with offspring and gosling survival in a semi-tame, long-term monitored, and individually marked flock of Greylag Geese in Grünau, Austria. We found that behavioural role differentiation between the parents varied with developmental phase, and thus with gosling age. Especially during the first 10 days after hatching, females were foraging more frequently than males, which were more vigilant and aggressive towards other flock members. Such differences between the sexes levelled out 20 to 30 days after hatching. In general, females stayed in closer proximity to their offspring than males. Gosling survival was high when the parents were relatively aggressive and emphasized vigilance rather than foraging behaviour. Hence, we show a direct link between pair partners' quality of parental investment and gosling survival.

Foraging, feeding, and physiological stress responses of wild wood mice to increased illumination and common genet cues

In nature, animals are exposed to a broad range of threats imposed by predators, which may strongly influence the ecology of prey species directly or indirectly by affecting their behavior via fear of predation. Here, we studied wood mice Apodemus sylvaticus behavioral and physiological responses to simulated predation risk. Risk avoidance was analyzed by live trapping with control traps and traps treated with feces of common genet Genetta genetta (direct cue of risk) under new moon nights and following by simulated full moon conditions (indirect cue). The time devoted to foraging behavior and capture time were analyzed by video recording mice activity around traps. Food intake was calculated based on the amount of bait remaining in each trap. Fecal corticosterone metabolites (FCMs) were measured by enzyme-immunoassay as indicators of physiological stress responses. Fewer wood mice were captured during full moon, yet only non-breeding adult males clearly avoided common genet odor. Mice were captured sooner at night during the simulated full moon conditions and later in predator-treated traps. Foraging activity was lower when individuals faced predator’s feces, but neither food intake nor FCM levels were affected by predation risk cues. Direct and indirect cues of predation risk selectively affected wood mice behavior, although behavioral responses seem to be modulated by different costs–benefit balances related to the individual’s perception of risk. The lack of physiological responses to predation risk cues suggests that wood mice did not perceive them as reliable stressors or the response was too small or transient to be measured by FCM.

Excretion patterns of coccidian oocysts and nematode eggs during the reproductive season in Northern Bald Ibis (Geronticus eremita)

Individual reproductive success largely depends on the ability to optimize behaviour, immune function and the physiological stress response. We have investigated correlations between behaviour, faecal steroid metabolites, immune parameters, parasite excretion patterns and reproductive output in a critically endangered avian species, the Northern Bald Ibis (Geronticus eremita). In particular, we related haematocrit, heterophil/lymphocyte ratio, excreted immune-reactive corticosterone metabolites and social behaviour with parasite excretion and two individual fitness parameters, namely, number of eggs laid and number of fledglings. We found that the frequency of excretion of parasites' oocysts and eggs tended to increase with ambient temperature. Paired individuals excreted significantly more samples containing nematode eggs than unpaired ones. The excretion of nematode eggs was also significantly more frequent in females than in males. Individuals with a high proportion of droppings containing coccidian oocysts were more often preened by their partners than individuals with lower excretion rates. We observed that the more eggs an individual incubated and the fewer offspring fledged, the higher the rates of excreted samples containing coccidian oocysts. Our results confirm that social behaviour, physiology and parasite burden are linked in a complex and context-dependent manner. They also contribute background information supporting future conservation programmes dealing with this critically endangered species.

Androgen response to social competition in a shoaling fish

Androgens respond to social challenges and this response has been interpreted as a way for males to adjust androgen-dependent behavior to social context. However, the androgen responsiveness to social challenges varies across species and a conceptual framework has been developed to explain this variation according to differences in the mating system and parental care type, which determines the regimen of challenges males are exposed to, and concomitantly the scope (defined as the difference between the physiological maximum and the baseline levels) of response to a social challenge. However, this framework has been focused on territorial species and no clear predictions have been made to gregarious species (e.g. shoaling fish), which although tolerating same-sex individuals may also exhibit intra-sexual competition. In this paper we extend the scope of this conceptual framework to shoaling fish by studying the endocrine response of zebrafish (Danio rerio) to social challenges. Male zebrafish exposed to real opponent agonistic interactions exhibited an increase in androgen levels (11-ketotestosterone both in Winners and Losers and testosterone in Losers). This response was absent in Mirror-fighters, that expressed similar levels of aggressive behavior to those of winners, suggesting that this response is not a mere reflex of heightened aggressive motivation. Cortisol levels were also measured and indicated an activation of the hypothalamic-pituitary-interrenal axis in Winners of real opponent fighters, but not Losers or in Mirror-fighters. These results confirm that gregarious species also exhibit an endocrine response to an acute social challenge.

Lack of genetic structure in greylag goose (Anser anser) populations along the European Atlantic flyway

Greylag goose populations are steadily increasing in north-western Europe. Although individuals breeding in the Netherlands have been considered mainly sedentary birds, those from Scandinavia or northern Germany fly towards their winter quarters, namely over France as far as Spain. This study aimed to determine the genetic structure of these birds, and to evaluate how goose populations mix. We used mitochondrial DNA and microsatellites from individuals distributed throughout the European Atlantic flyway, from breeding sites in Norway and the Netherlands to stopover and wintering sites in northern and south-western France. The mtDNA marker (CR1 D-Loop, 288 bp sequence, 144 ind.) showed 23 different haplotypes. The genetic distances amongst individuals sampled in Norway, northern France and the Netherlands were low (range 0.012-0.013). Individuals in south-western France showed a slightly higher genetic distance compared to all other sampling areas (ranges 0.018-0.022). The NJ tree does not show evidence of any single clades grouping together all individuals from the same geographic area. Besides, individuals from each site are found in different branches. Bayesian clustering procedures on 14 microsatellites (169 individuals) did not detect any geographically distinct cluster, and a high genetic admixture was recorded in all studied areas except for the individuals from the breeding sites in Norway, which were genetically very close. Estimation of migration rates through Bayesian inference confirms the scenario for the current mixing of goose populations.

Feather corticosterone content in predatory birds in relation to body condition and hepatic metal concentration

This study investigated the feasibility of measuring corticosterone in feathers from cryo-archived raptor specimens, in order to provide a retrospective assessment of the activity of the stress axis in relation to contaminant burden. Feather samples were taken from sparrowhawk Accipiter nisus, kestrel Falco tinnunculus, buzzard Buteo buteo, barn owl Tyto alba, and tawny owl Strix aluco and the variation in feather CORT concentrations with respect to species, age, sex, feather position, and body condition was assessed. In sparrowhawks only, variation in feather CORT content was compared with hepatic metal concentrations. For individuals, CORT concentration (pgmm(-1)) in adjacent primary flight feathers (P5 and P6), and left and right wing primaries (P5), was statistically indistinguishable. The lowest concentrations of CORT were found in sparrowhawk feathers and CORT concentrations did not vary systematically with age or sex for any species. Significant relationships between feather CORT content and condition were observed in only tawny owl and kestrel. In sparrowhawks, feather CORT concentration was found to be positively related to the hepatic concentrations of five metals (Cd, Mn, Co, Cu, Mo) and the metalloid As. There was also a negative relationship between measures of condition and total hepatic metal concentration in males. The results suggest that some factors affecting CORT uptake by feathers remain to be resolved but feather CORT content from archived specimens has the potential to provide a simple effects biomarker for exposure to environmental contaminants.

Endocrine regulation and sexual differentiation of avian copulatory sexually selected characters

Reproductive specializations in birds have provided intriguing model systems to better understand the role of endocrine mechanisms that regulate phenotype expression and the action of sexual selection. A comparative approach can elucidate how endocrine systems associated with control of sexual differentiation, sexual maturation, and reproductive physiology and behavior have diversified. Here we compare the copulatory sexually selected traits of two members of the galloanseriform superfamily: quail and ducks. Japanese quail have a non-intromittent penis, and they have evolved a unique foam gland that is known to be involved in post-copulatory sexual selection. In contrast, ducks have maintained a large intromittent penis that has evolved via copulatory male-male competition and has been elaborated in a sexually antagonistic race due to sexual conflict with females over mating. These adaptations function in concert with sex-specific and, in part, species-specific behaviors. Although the approaches to study these traits have been different, exploring the differences in neuroendocrine regulation of sexual behavior, development and seasonality of the foam gland and the penis side by side, allow us to suggest some areas where future research would be productive to better understand the evolution of novelty in sexually selected traits.

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.

Can faecal glucocorticoid metabolites be used to monitor body condition in wild Upland geese Chloephaga picta leucoptera?

The measurement of faecal glucocorticoid metabolites is used as a non-invasive technique to study stress in animal populations. They have been used most widely in mammals, and mammalian studies have also treated issues such as sample stability and storage methods. In birds, faecal corticosterone metabolite (CM) assays have been validated for a small number of species, and adequate storage under field conditions has not been addressed explicitly in previous studies. Furthermore, while it is well-established that baseline plasma corticosterone levels in birds rise with declining body condition, no study so far investigated if this relationship is also reflected in faecal samples. We here present data of a field study in wild Upland geese Chloephaga picta leucoptera on the Falkland Islands, testing different storage methods and investigating the relationship of faecal CM concentrations to body condition and reproductive parameters. We found that faecal CM measures are significantly repeatable within individuals, higher in individuals with lower body condition in both male and female wild Upland geese and higher in later breeding females with smaller broods. These results suggest that measuring faecal CM values may be a valuable non-invasive tool to monitor the relative condition or health of individuals and populations, especially in areas where there still is intense hunting practice.

Benefits of family reunions: social support in secondary greylag goose families

Social interactions are among the most potent stressors. However, social allies may diminish stress, increase success in agonistic encounters and ease access to resources. We studied the role of social support as a major mechanism for individual stress management in families of free-ranging greylag geese (Anser anser). Greylag geese are long-term monogamous, live in a female-bonded social system, and fledged offspring stay with their parents until the next breeding season ('primary families'). Should parents then fail to fledge young, subadults might rejoin them in summer after molt is completed ('secondary families'). We have previously shown that primary greylag goose families reap benefits from active social support in agonistic encounters, and also excrete lower levels of immuno-reactive corticosterone metabolites (CORT, 'passive social support'). Here we investigated how far active and passive social support continues in secondary goose families. Although we found that active support in agonistic encounters was almost absent in secondary families, subadult male geese won an increased number of agonistic encounters due to the mere presence of their secondary family. Particularly adult and subadult females benefited from passive social support through decreased CORT, whereas males did not. Decrease in the hormonal stress response during challenging situations, induced by social allies, may help the females' long-term energy management, thereby improving the odds for successful future reproduction. We discuss whether joining a secondary family may be an alternative tactic for young geese towards optimizing their start into a complex social life.

Annual pattern of fecal corticoid excretion in captive Red-tailed parrots (Amazona brasiliensis)

Annual patterns of fecal corticoid excretion were analyzed in the threatened Red-tailed parrot (Amazona brasiliensis) in captivity. Corticoid concentration over the 15 months of the study (mean +/- standard error, 12.6 +/- 0.32 ng g(-1), n = 585) was lowest around May (the southern Fall), and greatest around September (late winter), just prior to their normal breeding period. Corticoid excretion follows a seasonal pattern best explained by reproductive cycles rather than climate, although climate may be involved in the timing of corticoid excretion. Fecal corticoids also show promise as a tool to measure stress levels. We demonstrate that fecal corticoid measurement is a simple, yet efficient method for monitoring adrenocortical activity in captive, and perhaps wild, parrots. Monitoring adrenocortical activity can inform researchers about imposed stress in captivity, whether pair-bonds are forming in captive birds, and of the timing of breeding both in captivity and in nature.

Corticosterone metabolites in blue tit and pied flycatcher droppings: effects of brood size, ectoparasites and temperature

The hypothalamic-pituitary-adrenal (HPA) axis of birds induces the secretion of corticosterone (CORT) as a response to different ecological variables. In this study we tested experimentally if manipulations of brood size or ectoparasitism led to subsequent differences in the concentration of excreted CORT metabolites of adult and nestling blue tits (Cyanistes caeruleus). No significant effect of the manipulation of brood size was detected in adults or nestlings. No significant effect of ectoparasitism was detected in males or nestlings, although females from uninfested nests showed lower concentrations of excreted CORT metabolites. In addition, we analysed if weather conditions had an influence on the concentration of excreted CORT metabolites of blue tits and pied flycatchers (Ficedula hypoleuca) breeding in the same forest. We detected no effect of weather conditions on adults, but nestlings of both species showed a negative correlation between their excreted CORT metabolites and the average mean temperatures they were subjected to during their growth. This effect was not found in blue tits in a colder year, suggesting that the sensitivity of the HPA axis to ambient temperature may be subjected to interannual variation. Moreover, we found a positive effect of the maximum temperature on the day of sampling on the concentration of CORT metabolites of blue tit nestlings in one of the years. These results suggest that weather conditions may act as environmental stressors to which the HPA axis of blue tit and pied flycatcher nestlings may be sensitive.

Corticosterone excretion patterns and affiliative behavior over development in ravens (Corvus corax)

Averse effects of social stress may be buffered by the presence of social allies, which mainly has been demonstrated in mammals and recently also in birds. However, effects of socio-positive behavior prior to fledging in relation to corticosterone excretion in altricial birds have not been investigated yet. We here monitored corticosterone excretion patterns in three groups of hand raised juvenile ravens (n=5, 6 and 11) in the nest, post-fledging (May-July) and when ravens would be independent from their parents (September-November). We related these corticosterone excretion patterns to socio-positive behavior. Behavioral data were collected via focal sampling in each developmental period considered. We analyzed amounts of excreted immunoreactive corticosterone metabolites (CM) using enzyme immuno assays. We collected fecal samples in each developmental period considered and evaluated the most appropriate assay via an isolation stress experiment. Basal CM was significantly higher during the nestling period than post-fledging or when birds were independent. The time nestlings spent allopreening correlated negatively with mean CM. Post-fledging, individuals with higher CM levels sat close to (distance <50 cm) conspecifics more frequently and tended to preen them longer. When birds were independent and a stable rank hierarchy was established, dominant individuals were preened significantly longer than subordinates. These patterns observed in ravens parallel those described for primates, which could indicate that animal species living in a complex social environment may deal with social problems in a similar way that is not restricted to mammals or primates.

Individualities in a flock of free-roaming greylag geese: behavioral and physiological consistency over time and across situations

The concept of personality implies individual differences in behavior and physiology that show some degree of repeatability/consistency over time and across contexts. Most studies of animal personality, particularly studies of individuals' variation in physiological mechanisms, have been conducted on selected individuals in controlled conditions. We attempted to detect consistent behaviors as well as physiological patterns in greylag ganders (Anser anser) from a free-roaming flock living in semi-natural conditions. We tested 10 individuals repeatedly, in a handling trial, resembling tests for characterization of "temperaments" in captive animals. We recorded the behavior of the same 10 individuals during four situations in the socially intact flock: (1) a "low density feeding condition", (2) a "high density feeding condition", (3) a "low density post-feeding situation" and (4) while the geese rested. We collected fecal samples for determination of excreted immuno-reactive corticosterone (BM) and testosterone metabolites (TM) after handling trials, as well as the "low density feeding" and the "high density feeding" conditions. BM levels were very highly consistent over the repeats of handling trials, and the "low density feeding condition" and tended to be consistent over the first two repeats of the "high density feeding condition". Also, BM responses tended to be consistent across contexts. Despite seasonal variation, there tended to be inter-test consistency of TM, which pointed to some individual differences in TM as well. Aggressiveness turned out to be a highly repeatable trait, which was consistent across social situations, and tended to correlate with an individual's resistance during handling trials. Also, "proximity to the female partner" and "sociability" - the average number of neighboring geese in a close distance while resting - were consistent. We conclude that aggressiveness, "affiliative tendencies" and levels of excreted corticosterone and testosterone metabolites may be crucial factors of personality in geese.

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.

Measuring fecal glucocorticoid metabolites in mammals and birds: the importance of validation

In recent years, the noninvasive monitoring of steroid hormone metabolites in feces of mammals and droppings of birds has become an increasingly popular technique. It offers several advantages and has been applied to a variety of species under various settings. However, using this technique to reliably assess an animal's adrenocortical activity is not that simple and straightforward to apply. Because clear differences regarding the metabolism and excretion of glucocorticoid metabolites (GCMs) exist, a careful validation for each species and sex investigated is obligatory. In this review, general analytical issues regarding sample storage, extraction procedures, and immunoassays are briefly discussed, but the main focus lies on experiments and recommendations addressing the validation of fecal GCM measurements in mammals and birds. The crucial importance of scrutinizing the physiological and biological validity of fecal GCM analyses in a given species is stressed. In particular, the relevance of the technique to detect biologically meaningful alterations in adrenocortical activity must be shown. Furthermore, significant effects of the animals' sex, the time of day, season, and different life history stages are discussed, bringing about the necessity to seriously consider possible sex differences as well as diurnal and seasonal variations. Thus, comprehensive information on the animals' biology and stress physiology should be carefully taken into account. Together with an extensive physiological and biological validation, this will ensure that the measurement of fecal GCMs can be used as a powerful tool to assess adrenocortical activity in diverse investigations on laboratory, companion, farm, zoo, and wild animals.

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.

Hormonal correlates of siblicide in Nazca boobies: support for the Challenge Hypothesis

The androgen hormone testosterone (T) mediates vertebrate aggression in many contexts and according to the Challenge Hypothesis is up-regulated during social challenges. While originally applied to challenges experienced by breeding adults, we show for the first time that T is similarly up-regulated during deadly sibling aggression in young birds. When two nestling Nazca boobies hatch, one--usually the older chick--virtually always kills the other chick by pushing it from the nest. We compared concentrations of T, dehydroepiandrosterone (DHEA; a precursor of T), and corticosterone (Cort; a stress hormone) of chicks at various stages. T was elevated during fights in both chicks in two-chick broods, but not before and after fights, and not in chicks lacking a nest mate. DHEA was elevated 1 day after hatching and declined with age but appeared not to vary in concert with aggression. Cort did not vary across fighting and nonfighting periods. In conjunction with an earlier study [Tarlow, E.M., Wikelski, M., Anderson, D.J., 2001. Hormonal correlates of siblicide in Galapagos Nazca boobies. Horm. Behav. 40:14-20], these results indicate that T is temporarily up-regulated around the time of fights, as predicted by the Challenge Hypothesis. Our data suggest a general role for T during challenges at any time in life, not just during breeding.

A comparative methodical study of the faecal steroid analysis on birds: looking for a valid method of testosterone determination

In a comparative study, a relatively simple and high sensitivity method was developed for analysis of testosterone-equivalent(s) in the faeces of different bird species. To determine the recovery of extractions and purifications, tritium-labelled testosterone was added to the wet samples. Then the samples were treated with sodium dodecil sulphate (SDS), an emulsificator to "open-up" the complex, lipid-coated particles of faecal samples. This emulsification resulted in the decrease of the quantity of interfering substances after diethyl-ether extraction and the linearity of the measured testosterone equivalents from aliquots in the range of 2 and 10 mg of faeces. In the RIA, we applied a group specific polyclonal testosterone antibody which cross-reacted with reduced metabolites and at a certain level with sulphate conjugates as well. The use of Helix enzymes did not modified significantly the results of the analysis relating to a low level of conjugated androgens in the faecal extracts. The biological validity of the method was tested on domestic cockerels, where between the plasma and faecal testosterone values a four hours phase shift was observed, with a correlation of 0.6355. This method is suitable for "non invasive", behavioural-ethological studies.

Social allies modulate corticosterone excretion and increase success in agonistic interactions in juvenile hand-raised graylag geese (Anser anser)

In mammals, support by a social partner may reduce stress levels and ease access to resources. We investigated the effects of the passive presence of a nearby social ally on excreted corticosterone immunoreactive metabolites and behaviour in juvenile graylag geese (Anser anser). Two groups of hand-raised juveniles (N1 = 9, N2 = 3) were tested over 1 year by positioning humans of different familiarity (i.e., the human foster parent, a familiar human, a nonfamiliar human, no human) at a standard distance to the focal geese. Their success in agonistic interactions significantly decreased with age and with decreasing familiarity of the accompanying human. The humans present modulated the excretion of corticosterone immunoreactive metabolites, with the strongest effects recorded after fledging when corticosterone metabolites were also positively correlated with agonistic behaviour. This suggests that a human foster parent may provide similar supportive benefits as goose parents do in natural families. We discuss the benefits of social alliances with regard to the integration into the flock, access to resources, and life history.

Measurement of plasma corticosterone and fecal glucocorticoid metabolites in the chicken (Gallus domesticus), the great cormorant (Phalacrocorax carbo), and the goshawk (Accipiter gentilis)

A method for the non-invasive measurement of glucocorticoid metabolites in feces of chickens was established and validated. After high-performance liquid chromatography (HPLC) the presence of at least two fecal immunoreactives was demonstrated, one co-eluting with authentic corticosterone, whereas the second substance migrates close to corticosterone sulphate. We investigated the relationship between corticosterone in blood plasma obtained by a vena brachialis catheter and fecal samples in groups of five chickens after an ACTH and a dexamethasone injection to stimulate and to suppress adrenal activity. A control group received a saline injection. After ACTH plasma cortisol concentrations increased 16-fold after 1.5 h to levels between 19 and 38 ng/ml and dropped to pre-treatment levels (1.1-2.5 ng/ml) 4h after stimulation. Dexamethasone did not result in a distinct suppression of adrenocortical activity and plasma corticosterone dropped only slightly below pre-treatment levels. The concentrations in fecal metabolites corresponded to the changes in the levels of biological active hormone in plasma. Fecal peak excretion (105-295 ng/g) was obtained with a delay of approximately 4 h compared to plasma. The profile obtained after ACTH challenge reflected a broader and dampened pattern of glucocorticoid secretion and provided a more integrated measure of adrenal activity. Dexamethasone treatment did not induce a measurable decrease in fecal metabolites and concentrations fluctuated around a mean of 30.0+/-9.9 ng/g, almost identical to those obtained from the saline treatment group (29.4+/-13.9 ng/g). In a separate experiment the effect of an alternative capture method (remote-controlled injection system) was investigated in cormorants. Plasma corticosterone measurements revealed a significantly diminished stress reaction compared to traditional trapping (1.24+/-0.78 vs. 10.9+/-12.1 ng/ml). Investigations whether goshawk nestlings infected with Trichomas gallinae differ in fecal corticosterone metabolite concentrations compared to healthy subjects revealed no significant changes. However, a significant correlation was found between the glucocorticoid metabolite concentrations and the number of nestlings per nest. The demonstration that adrenal activity can be detected by the assay is a prerequisite that ecologically meaningful levels of imposed stress can be validated. Therefore, non-invasive measurements of fecal metabolites are a promising perspective to monitor stress in birds.

Comparative analysis of male androgen responsiveness to social environment in birds: the effects of mating system and paternal incubation

Male androgen responses to social challenges have been predicted to vary with mating system, male-male aggressiveness, and the degree of paternal investment in birds ("challenge hypothesis," Am. Nat. 136 (1990), 829). This study focused on the interspecific predictions of the challenge hypothesis. Comparative methods were used to control for effects of the phylogenetic relatedness among the sampled species. Male androgen data of 84 bird species were collected from literature records on seasonal androgen patterns. From these, the androgen responsiveness (AR) was calculated as described in the original challenge hypothesis (i.e., maximum physiological level/breeding baseline). Scatterplots of AR versus mating strategy, male-male aggressiveness, and the degree of paternal care confirmed the expected interspecific patterns. When phylogenetic analyses were performed among all of the sampled species, the effects of paternal investment disappeared while the AR remained covarying to a high degree with mating system and male-male aggressiveness. Although these mechanisms may be different at the intraspecific level, this suggests that interspecific differences of AR in male birds may have evolved in response to changes of mating strategies, rather than in response to altered paternal duties. However, control for phylogeny among the subsample of 32 passerine species revealed that if any paternal investment contributed to the observed variance in AR, then the change from "no male incubation" to "male shares incubation duties" represented the most effective, whereas the male's contribution to feeding offspring did not explain the observed variation of AR.

Behavioral and adrenocortical responses to mate separation and reunion in the zebra finch

The adaptive value of social affiliation has been well established. It is unclear, however, what endogenous mechanisms may mediate affiliative behavior. The Australian zebra finch (Taeniopygia guttata) breeds colonially and adults maintain lifelong pair bonds that may be disrupted in the wild due to high mortality rates. Many of its natural, social behaviors are maintained in laboratory conditions, making this species well suited for studying the mechanisms of affiliation. This study examines the behavioral and neuroendocrine responses to pair mate separation and reunion in zebra finches. We measured plasma corticosterone (CORT) and behavioral changes following separation from a pair bonded mate, and again upon reintroducing the mate or an opposite-sex cagemate. Plasma CORT concentrations were: (1). elevated during pair mate separation, even in the presence of other same-sex individuals, and (2). reduced to baseline upon reunion with the pair mate but not upon re-pairing with a new opposite-sex partner. These findings show that zebra finches exhibit hormonal responses to separation and reunion specifically with a bonded pair mate and not with other familiar conspecifics. In addition, alterations in behavior during separation and reunion are consistent with monogamous pair bond maintenance. This study presents evidence for adrenocortical involvement in avian pair bonding, and for hypothalamic-pituitary-adrenal activation in response to an ecologically relevant social stressor.

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

Traditionally androgen concentrations are measured invasively in blood plasma. However, non-invasive methods to detect androgens are desirable, as this reduces interference with the natural behavior of the study species and multiple samples can be obtained relatively easy. The aim of this study was to validate a method to measure androgens non-invasively in excrements of male European stonechats (Saxicola torquata rubicola). Extracts of excrements of a male stonechat injected with [3H]testosterone ([3H]T) were chromatographically separated using high performance liquid chromatography (HPLC). The resulting HPLC fractions were then analyzed with a radioimmunoassay against testosterone (T-RIA). The results showed that the assay picked up major metabolites of [3H]T. The physiological relevance of excreted androgen metabolites was further validated by showing that injection of exogenous GnRH to seven males led to a significant increase in excreted androgen metabolites. In contrast, androgen metabolite levels of six saline-injected control males did not increase. Furthermore, excrements from nine males were collected from January until April to see whether the typical seasonal increase in testosterone levels can also be traced when measuring excreted androgen metabolites. As expected, there was a significant seasonal increase in androgen metabolite concentrations. Thus, the T-RIA measures androgen metabolites in droppings of male European stonechats and to our knowledge this study represents the first validation of a non-invasive androgen assay in a passerine bird.

Excreted metabolites of gonadal steroid hormones and corticosterone in greylag geese (Anser anser) from hatching to fledging

Steroid hormones play major roles in the organization of the phenotype and in the activation of behavior. From hatching to fledging, they are involved in growth, development, and learning. We investigated the relationship between the ontogenetic patterns of steroid hormones and the sexual and social development of greylag goslings (Anser anser). Two groups of individually marked goslings (n = 10/5) were hand-raised under near-field conditions. 17beta-OH-androgen (AM), estrogen (EM), and corticosterone (BM) immunoreactive metabolites were measured noninvasively by enzyme immunoassay of individual fecal samples. Feces were regularly sampled from hatching to fledging. All excreted steroids were found to peak at hatching and to decrease thereafter. Gonadal steroids fluctuated more than BM, which remained at low levels throughout ontogeny after a slow decrease during the first 20 days. The pattern of BM is discussed in relation to learning processes (i.e., filial imprinting) and social stress. It is suggested that high initial BM may constrain energy allocation to growth. AM increased around the age of 20 days, when the feathers start growing, and later, together with EM, at the age of 40 days. These elevated values of gonadal steroids are discussed in relation to the sensitive phase of sexual imprinting. Females show higher EM levels than males throughout ontogeny. Furthermore, the ratio of excreted estrogen to androgen (EM/AM) of females before fledging correlates with the number of hatched and fledged goslings in their first years of reproduction. In conclusion, our data suggest a role for steroid hormones in the modulation of behavioral and morphological development in the precocial greylag geese, in agreement with the organizational-activational hypothesis.

Seasonal relationships between plasma and fecal testosterone in response to GnRH in domestic ganders

In two groups (eight individuals each) of socially acquainted, outdoor-kept, domestic ganders (male Hungarian white: Anser domesticus), basal and GnRH-stimulated plasma testosterone (T) concentrations were compared with fecal testosterone metabolites (TM) in and between three seasons, spring peak of reproductive activity, summer photorefractoriness, and fall sexual reactivation. Plasma was sampled 90 min following the challenge and T was analyzed by radioimmunoassay following the GnRH challenge. Fecal TM were measured by enzyme immunoassay using two group-specific antibodies against 17beta-OH-androgens or a novel antibody against 17-oxo groups, which was found to react with major testosterone metabolites without prior hydrolytic deconjugation. Baseline plasma T and systemic levels were high in spring and fall but low in summer. Plasma T increases in response to GnRH were followed by significantly elevated fecal TM levels 2 to 6 h following the challenge in spring and fall. In fall, at high plasma T levels, fecal TM levels were disproportionally lower than in spring. Variability of TM levels was two to five times higher in feces than in plasma, which explains why correlations between individual plasma T and fecal TM levels generally remained nonsignificant. This points to a low-level short-term relationship between the excreted TM and the plasma T levels. However, the reliability of the method was demonstrated by standard inter- and intraassay variabilities and by a high correspondence between results obtained by the two assays. It is suggested that, with appropriate sample size, fecal TM reflects plasma T increase. However, fecal TM was more variable than the plasma T, and fecal TM responses to GnRH did not always parallel the plasma T response. In addition, seasonal changes in androgen excretion regimes must be taken into account.