Measurement of corticosterone metabolites in birds' droppings: an analytical approach

Beyond Glucocorticoids: Integrating Dehydroepiandrosterone (DHEA) into Animal Welfare Research

Animal welfare researchers are committed to identifying novel measures for enhancing the quality of life of individual animals. Recently, welfare scientists have emphasized the need for tracking multiple indicators of an animal's behavioral, emotional and mental health. Researchers are currently focused on integrating non-invasive physiological biomarkers to gain insight into an individual's welfare status. Most commonly, the animal welfare community has analyzed glucocorticoid hormones and their metabolites as a measure of stress. While glucocorticoids provide valuable information about hypothalamic-pituitary-adrenal (HPA) axis activity, there are limitations to utilizing these hormones as the sole measure of long-term stress and welfare. Other biomarkers, such as dehydroepiandrosterone and its sulfate ester-collectively referred to as DHEA(S)-help provide a more complete picture of HPA activity. DHEA(S) counteracts the effects glucocorticoids by having anti-aging, immune-enhancing and neuroprotective properties. Recent studies have examined the ratio of glucocorticoids to DHEA(S) as a way to better understand how the HPA axis is functioning. There is evidence that this ratio serves as an indicator of immune function, mental health, cognitive performance and overall welfare. We review studies that employed the glucocorticoid:DHEA(S) ratio, outline methodological considerations and discuss how researchers can integrate glucocorticoids, DHEA(S) and the glucocorticoid:DHEA(S) ratio into welfare assessments.

Low rank and primiparity increase fecal glucocorticoid metabolites across gestation in wild geladas

Integrative behavioral ecology requires accurate and non-invasive measures of hormone mediators for the study of wild animal populations. Biologically sensitive assay systems for the measurement of hormones and their metabolites need to be validated for the species and sample medium (e.g. urine, feces, saliva) of interest. Where more than one assay is available for hormone (metabolite) measurement, antibody selection is useful in identifying the assay that tracks changes in an individuaĺs endocrine activity best, i.e., the most biologically sensitive assay. This is particularly important when measuring how glucocorticoids (GCs) respond to the subtle, additive effects of acute stressors during a predictable metabolic challenge, such as gestation. Here, we validate a group-specific enzyme immunoassay, measuring immunoreactive 11β-hydroxyetiocholanolone, for use in a wild primate, geladas (Theropithecus gelada). This group-specific assay produced values correlated with those from a previously validated double-antibody, corticosterone ¹²⁵I radioimmunoassay. However, the results with the group-specific assay showed a stronger response to an ACTH challenge and identified greater variation in gelada immunoreactive fecal glucocorticoid metabolites (iGCMs) compared with the corticosterone assay, indicating a higher biological sensitivity for assessing adrenocortical activity. We then used the group-specific assay to: (1) determine the normative pattern of iGCM levels across gelada gestation, and (2) identify the ecological, social, and individual factors that influence GC output for pregnant females. Using a general additive mixed model, we found that higher iGCM levels were associated with low rank (compared to high rank) and first time mothers (compared to multiparous mothers). This study highlights the importance of assay selection and the efficacy of group-specific assays for hormonal research in non-invasively collected samples. Additionally, in geladas, our results identify some of the factors that increase GC output over and above the already-elevated GC concentrations associated with gestation. In the burgeoning field of maternal stress, these factors can be examined to identify the effects that GC elevations may have on offspring development.

Validation of a noninvasive technique to quantify stress in northern bobwhite (Colinus virginianus)

Examination of the endocrine system through non-invasive fecal sampling may improve population management more than using demographic indicators alone. By addressing the physiological mechanisms that are influencing fitness, management actions can be proactively developed to alleviate stressors. Proactive determination of vulnerable populations is critical for species of concern, such as the Northern Bobwhite (Colinus virginianus), which have suffered decades of population decline. We validated an assay to noninvasively measure the adrenocortical response of captive reared bobwhite through fecal corticosterone metabolites (FCM). All individuals received three sequential 48-hour treatments in which samples were collected every 4 hours, including a reference period, an adrenocorticotropic hormone (ACTH) challenge and a biological stressor (exposure to a hunting dog). Reference FCM values had a mean concentration of 16.75 pg/mg (95% CrI: 13.68, 19.91) with adrenocortical activity increasing by 73% for the duration of the ACTH challenge (29.00 pg/mg; CrI: 25.01, 33.78). FCM concentrations remained similar to that of the reference levels during the biological stressor (16.56 pg/mg; CrI: 13.33, 19.92). Our study validates the use of feces to detect changes in FCM levels in our subject species but also demonstrates the complexity of FCM and the importance of both physiological and biological validation prior to field implementation.

Faecal glucocorticoid metabolites as a measure of adrenocortical activity in polar bears (Ursus maritimus)

Analysis of faecal glucocorticoid metabolites (FGMs) is frequently applied to assess adrenocortical activity in animal conservation and welfare studies. Faecal sample collection is non-invasive and feasible under field conditions. FGM levels are also less prone to circadian rhythms, episodic fluctuations and short acute stressors than glucocorticoid (GC) levels obtained from other matrices, for example blood or saliva. To investigate the suitability of FGM measurement in polar bears (Ursus maritimus), a species listed as Vulnerable by the IUCN (International Union for Conservation of Nature), a cortisol enzyme immunoassay (EIA) was biologically validated by demonstrating a significant increase in FGMs after five zoo-to-zoo transports. In addition to validating the method, the study also documented an average delay of 7 h until the first occurrence of food colorants in the monitored polar bears, which provides essential information for future studies. After validation, the assay was applied to measure FGM concentrations of five polar bears over a 1-year period. Several pre-defined potentially stressful events were recorded in an event log to measure their effect on FGM concentrations. A mixed model analysis revealed significant increases in FGM concentrations after social tension and environmental changes, whereas season and sex had no significant effect. The study demonstrates that the applied cortisol EIA is suitable for measuring FGM levels in polar bears and that using a carefully validated assay for FGM analysis in combination with a detailed sampling protocol can serve as a valuable tool for evaluating mid- to long-term stress in polar bears. FGM levels can be used to monitor stress in captive polar bears in order to optimize housing conditions but also to elucidate stress responses in wild populations for targeted conservation measures.

ACTH Stimulation Induced Self-Mutilation Behavior in the Golden Conure (Guaruba guarouba)

Simple Summary

Psittacidae are very susceptible to chronic stress and behavioral disorders. We report a successful physiological validation of an enzyme immunoassay for the non-invasive monitoring of adrenocortical activity and, thus, stress in the golden conure. In addition, as an incidental finding, we demonstrate a link between increased glucocorticoid levels and behavioral disorders. Our results are of great relevance for conservation projects and endocrine-behavioral studies of captive golden conures, where the stress evaluation is a fundamental part of animal welfare programs.

Abstract

Psittacidae are very susceptible to chronic stress and behavioral disorders. Information regarding the endocrinology of the golden conure is scarce, especially about adrenocortical activity. Endocrine studies using non-invasive methods are useful, because they allow longitudinal analysis with high numbers of samples without causing additional stress and are viable in the psittacidae management. The objective was to physiologically validate an enzyme immunoassay for measuring glucocorticoid metabolites (GCMs) in this species. Serial droppings were collected from 16 animals. First, one subgroup received adrenocorticotropic hormone (ACTH; Synacthen Depót^®) and the other group served as controls. This procedure was reversed afterwards. All birds presented self-mutilation approximately 6 h after the ACTH injection. This behavior disappeared after two days. Peak concentrations (on average nine times higher than baseline values) of GCMs were found 6 (4–8) h after ACTH administration; in all (but one) animals also a second peak was found 14 (10–20) h post injection. GCM levels returned to the baseline after 24 h. We physiologically validated a cortisone enzyme immunoassays to measure adrenocortical activity in the golden conure. Such non-invasive methods are important for studies, which are related to welfare, reproductive, and conservation programs. In addition, we could demonstrate a link between increased glucocorticoid levels and behavioral disorders.

Measurement of Fecal Testosterone Metabolites in Mice: Replacement of Invasive Techniques

Testosterone is the main reproductive hormone in male vertebrates and conventional methods to measure testosterone rely on invasive blood sampling procedures. Here, we aimed to establish a non-invasive alternative by assessing testosterone metabolites (TMs) in fecal and urinary samples in mice. We performed a radiometabolism study to determine the effects of daytime and sex on the metabolism and excretion pattern of radiolabeled TMs. We performed physiological and biological validations of the applied EIA to measure TMs and assessed diurnal fluctuations in TM excretions in male and female mice and across strains. We found that males excreted significantly more radiolabeled TMs via the feces (59%) compared to females (49.5%). TM excretion patterns differed significantly between urinary and fecal samples and were affected by the daytime of ³H-testosterone injection. Overall, TM excretion occurred faster in urinary than fecal samples. Peak excretion of fecal TMs occurred after 8 h when animals received the ³H-testosterone in the morning, or after 4 h when they received the ³H-testosterone injection in the evening. Daytime had no effect on the formed TMs; however, males and females formed different types of TMs. As expected, males showed higher fecal TM levels than females. Males also showed diurnal fluctuations in their TM levels but we found no differences in the TM levels of C57BL/6J and B6D2F1 hybrid males. Finally, we successfully validated our applied EIA (measuring 17β-hydroxyandrostane) by showing that hCG (human chorionic gonadotropin) administration increased TM levels, whereas castration reduced them. In conclusion, our EIA proved suitable for measuring fecal TMs in mice. Our non-invasive method to assess fecal TMs can be widely used in various research disciplines like animal behavior, reproduction, animal welfare, ecology, conservation, and biomedicine.

Stress in captive Blue-fronted parrots (Amazona aestiva): the animalists' tale

Understanding stress physiology is crucial for species management because high levels of stress can reduce reproduction and the individual's ability to face threats to survive. One of the most popular methods for non-invasive monitoring of animal endocrine status is the glucocorticoid (GC) metabolite measurements, which can provide important information about how animals are affected by their surrounding environment. Here, we carried out the biological validation of corticosterone enzyme immunoassays (EIAs), which together with a cortisol EIA was used to quantified the concentrations of urofaecal GC metabolites (uGCMs) in wild and captive Blue-fronted amazon parrots (Amazona aestiva). Urofaecal GC concentrations were significantly higher (P < 0.05) in free-living parrots (157.9 ± 18.5 ng cortisol/g and 61.14 ± 23.5 ng corticosterone/g dry urofaecal sample) than in those kept in captivity, which showed the comparable levels of GC metabolites independently of the management system applied. The higher uGCM levels obtained in the wild population point to an adaptive response for survival and species propagation in a more challenging environment, in comparison with captive animals. Furthermore, the lower uGCM concentrations in captive parrots may indicate an adaptive capacity of the species A. aestiva to captivity and its potential as a legal pet. The corticosterone EIA applied in this study proved to be an effective technique for the adrenocortical activity monitoring in this species. We discuss our findings considering the management and destiny given to wild-caught birds that are kept in confinement or returned to nature.

Monitoring corticoid metabolites in urine of white-tailed sea eagles: Negative effects of road proximity on breeding pairs

The white-tailed sea eagle (Haliaeetus albicilla) is known to be sensitive to disturbance. To better understand potential stressors, we measured corticosterone metabolite levels in H. albicilla excreta and recorded the nest success of breeding pairs. We tested the ability of four enzyme immunoassays (EIA) to measure urinary glucocorticoid metabolites (uGM) in the excreta of one adult female eagle subjected to a controlled physiological stress treatment. We identified corticosterone-21-HS to be the most sensitive EIA to changes in uGM concentration. To exclude a sex bias, we confirmed the assay's applicability with samples collected from similar stress treatments in two juvenile males. We used the identified EIA to measure uGM in wild breeding pairs and tested effects of disturbance. Breeding pairs nesting closer to roads and paths had higher uGM concentrations (p = 0.02), which is likely an effect of human recreational activity and disturbance. There was no difference in uGM concentrations between failed and successful nests. Our results highlight the potential impact of road and path proximity on white-tailed sea eagles, with potential importance for species management and conservation, particularly with respect to nest protection zone legislation.

Faecal metabolites and hair cortisol as biological markers of HPA-axis activity in the Rocky mountain goat

Monitoring glucocorticoids in faeces and hair is increasingly used in ecological studies and provides a powerful and minimally intrusive mean to identify physiological challenges faced by wild animals. Using a cortisol and a corticosterone immunoassays, we conducted an adrenocorticotropic (ACTH) challenge with five weekly repeated injections to validate the use of faecal glucocorticoid metabolites and hair cortisol concentration as biological markers of the HPA-axis activity in captive mountain goats (Oreamnos americanus). We also investigated the effect of endogenous (age, sex, reproductive status) and methodological (faecal sample collection date, freezing delay and hair type) variables on cortisol values using faecal and hair samples collected from marked wild mountain goats during a long-term study. The cortisol enzyme immunoassay was reliable for mountain goat faeces and hair, and was sensitive enough to detect a clear rise in glucocorticoid concentration following ACTH injections for both matrices. Age and sex had no detectable effect on faecal glucocorticoid metabolites, but hair cortisol concentration was higher in kids and yearlings than in older goats, and lower in adult males compared to adult females. Reproductive status had no detectable effect on both faecal and hair measurements. Faecal metabolite concentrations increased with sample collection date in late spring until mid-summer and decreased afterward until early fall. Guard hair had nearly twice as much cortisol per gram as undercoat hair. Prolonged delay to freezing reduced the concentration of faecal glucocorticoid metabolites, but degradation seemed limited when samples were exposed to wind and sun or when ambient temperature was low. We conclude that faeces and hair can be used as valid biomarkers of the HPA-axis activity in mountain goat provided that confounding variables are taken into account when interpreting measurements.

Stressful living in lower-quality habitats? Body mass, feeding behavior and physiological stress levels in wild wood mouse populations

Wild populations are continuously subjected to changes in environmental factors that pose different challenges. Body condition and hormones have been commonly used as health indicators due to their potential correlation with fitness. In the present study, we analyzed whether habitats of different quality influenced body mass, food intake and physiological stress levels in wild wood mice (Apodemus sylvaticus). Field work was seasonally carried out in Holm oak woods and pine forests in central Spain. A total of 93 wood mice from 4 different populations (2 per habitat type) were live-trapped. From each captured individual we noted body mass and food intake, measured as the amount of bait remaining in each trap. The physiological stress levels were measured non-invasively in collected fresh feces by quantifying fecal corticosterone metabolites (FCM) with a 5a-pregnane-3ß,11ß, 21-triol-20-one enzyme immunoassay. Wood mice abundances decreased from spring to summer, were higher in Holm oak woods than in pine forests and also resulted in different age-class distribution between both habitats. Individuals inhabiting pine forests showed a lower body mass and increased food intake, probably because of the comparatively lower food quality and availability in this habitat. Furthermore, these individuals showed increased physiological stress levels, likely due to the lower quality habitat in relation to both food and vegetation cover availability. Overall, besides affecting local wood mouse abundance, our study underscores the effect of habitat quality on body mass, food intake and the endocrine stress response. Considering the wood mouse's pivotal position in ecosystems, these results could help in the understanding of environmental traits hampering the viability of wild populations.

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

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

Does persistent snowpack inhibit degradation of fecal stress indicators?

Physiological stress in wildlife can be a useful indicator of a population's response to environmental factors. By using non-invasive endocrinological techniques, such as fecal sampling, potential confounding factors associated with the stress of capture can be avoided. A potential drawback of fecal sampling, however, is degradation of samples which may produce aberrant measurements of fecal glucocorticoid metabolites. In vertebrates, glucocorticoids, such as corticosterone, become elevated in response to stress. We sought to gauge the reliability of measurement of fecal glucocorticoid metabolites from white-tailed deer (Odocoileus virginianus) fecal samples exposed to a temperate winter with substantial snow cover and cold temperatures for up to 90 days, by repeatedly subsampling fecal samples every 10 days and performing a corticosterone enzyme-linked immunosorbent assay (ELISA). Measurements of fecal glucocorticoid metabolites at 10 days were consistent with initial measurements, after which (20 days) they became aberrant following a period of thawing. Consequently, glucocorticoid metabolite levels in feces appear to remain stable under ambient conditions if temperatures remain below freezing at least for 10 days. While it's possible that samples may remain useful beyond this time frame based on previous laboratory studies of samples stored in a freezer, further work is needed to determine how samples weather in situ under extreme cold (e.g. Arctic) or periods of partial thawing.

Non-invasive measurement of glucocorticoids: Advances and problems

Glucocorticoids (GCs; i.e. cortisol/corticosterone) are a central component of the stress response and thus their measurement is frequently used to evaluate the impact of stressful situations. Their metabolites from faeces of various animal species are more and more taken as a non-invasive aid to assess GC release and thus adrenocortical activity. The current literature review includes an extensive collection (1327 papers) and evaluation (see also Supplementary Tables) of the literature on faecal cortisol/corticosterone metabolite (FCM) analysis published to date. It aims at giving reference for researchers interested in implementing FCM analysis into their study or seeking to improve such methods by providing background knowledge on GC metabolism and excretion, conveying insights into methodological issues and stating caveats of FCM analysis and by highlighting prerequisites for and some examples of a successful application of such methods. Collecting faecal samples and analysing FCMs may appear simple and straightforward, but researchers have to select and apply methods correctly. They also need to be aware of the many pitfalls and potentially confounding factors and, last but not least, have to carefully interpret results. Applied properly, measurement of FCMs is a powerful non-invasive tool in a variety of research areas, such as (stress) biology, ethology, ecology, animal conservation and welfare, but also biomedicine.

Evidence of embryonic regulation of maternally derived yolk corticosterone

In recent years, the potential for maternal stress effects to adaptively alter offspring phenotype has received considerable attention. This research has identified offspring traits that are labile in response to maternal stress; however, an understanding of the mechanisms underlying these effects is lagging and is crucial to appreciating the significance of this maternal effect. In the present study, we sought to better understand maternal stress effects by examining the potential for embryonic regulation of corticosterone exposure, determining the phenotypic consequences of elevated corticosterone during development, and characterizing the levels of maternally transferred corticosterone in unmanipulated eggs using Trachemys scripta By dosing eggs with tritiated corticosterone and tracking the steroid throughout development, we found that most corticosterone is metabolized, and less than 1% of the corticosterone dose reaches the embryo as free corticosterone. We also found that exogenous dosing of corticosterone, in concentrations sufficient to overwhelm embryonic metabolism, reduces embryonic survival and negatively impacts hatchling traits important to fitness. Our results demonstrate that concentrations of maternal corticosterone in the yolks of unmanipulated eggs are low and are significantly lower than the doses of corticosterone required to elicit phenotypic effects in hatchlings. Taken together, these results provide evidence that both the embryo and the female may minimize corticosterone accumulation in the embryo to avoid reductions in embryonic survival and negative impacts on offspring phenotype and fitness.

Opportunities and challenges associated with fecal progesterone metabolite analysis

Conventionally, plasma or milk progesterone evaluations are used to determine the reproductive status of female animals. Collection of such samples is often associated with difficulties of animal handling and restraint. Measurable quantities of progesterone metabolites are found in feces of animals. Their concentrations are known to be well correlated to plasma progesterone levels and are, therefore, used as non-invasive samples for assessing reproductive function in a wide range of animal species. Although the analysis of fecal progesterone metabolites has been widely accepted in many laboratories, several factors are known to affect the results from this valuable analytical technique. Some of these factors include storage/transportation media for fecal samples, type of solvent that is used for extraction of progesterone metabolites from feces, and the type and sensitivity of an assaying technique employed. Although fecal progesterone metabolites analysis is associated with some difficulties, it can effectively be used to monitor reproductive function in a wide range of animal species. This review aims to highlight the usefulness of fecal progesterone metabolite analysis as a non-invasive technique in monitoring reproductive function in animals. The article mainly focuses on the many opportunities and challenges associated with this analytical technique.

Glucocorticoid measurement in plasma, urates, and feathers from California condors (Gymnogyps californianus) in response to a human-induced stressor

Vertebrates respond to stressful stimuli with the secretion of glucocorticoid (GC) hormones, such as corticosterone (CORT), and measurements of these hormones in wild species can provide insight into physiological responses to environmental and human-induced stressors. California condors (Gymnogyps californianus) are a critically endangered and intensively managed avian species for which information on GC response to stress is lacking. Here we evaluated a commercially available I125 double antibody radioimmunoassay (RIA) and an enzyme-linked immunosorbent assay (ELISA) kit for measurement of CORT and GC metabolites (GCM) in California condor plasma, urate, and feather samples. The precision and accuracy of the RIA assay outperformed the ELISA for CORT and GCM measurements, and CORT and GCM values were not comparable between the two assays for any sample type. RIA measurements of total CORT in condor plasma collected from 41 condors within 15 minutes of a handling stressor were highly variable (median = 70 ng/mL, range = 1-189 ng/mL) and significantly different between wild and captive condors (p = 0.02, two-tailed t-test, n = 10 wild and 11 captive). Urate GCM levels (median = 620 ng/g dry wt., range = 0.74-7200 ng/g dry wt., n = 216) significantly increased within 2 hr of the acute handling stressor (p = 0.032, n = 11 condors, one-tailed paired t-test), while feather section CORT concentrations (median = 18 pg/mm, range = 6.3-68 ng/g, n = 37) also varied widely within and between feathers. Comparison of multiple regression linear models shows condor age as a significant predictors of plasma CORT levels, while age, sex, and plasma CORT levels predicted GCM levels in urates collected within 30 min of the start of handling. Our findings highlight the need for validation when selecting an immunoassay for use with a new species, and suggest that non-invasively collected urates and feathers hold promise for assessing condor responses to acute or chronic environmental and human-induced stressors.

The landscape of fear: Why some free-ranging rodents choose repeated live-trapping over predation risk and how it is associated with the physiological stress response

Live trapping is an essential element of field ecological studies. However, the act of trapping provides two types of conditional benefits (food from the bait when hungry, and refuge from a predator when threatened) against one type of drawback (confinement). Our understanding of how animals assess the two benefits against the lone risk determines how we interpret classic field studies in chemical ecology and wildlife management. Here, we studied wood mice responses to these risks and rewards of field trapping by examining experience through recapture and faecal corticosterone metabolites (FCM) as a physiological response indicator. Wood mice were live-trapped in two different plots subjected to two distinct phases: phase 1, absence of predator cues, and phase 2, in which traps were treated with red fox faeces. During phase 1, the recapture percentage was lower indicating that mice avoided traps while FCM levels in recaptured mice were higher. On the contrary, during phase 2, despite the total number of captures was lower we found an increase in the recapture percentage and FCM levels did not increase in recaptured mice. Our results suggest that under increased risk perception traps could be likely considered as a suitable shelter and thus, for some individuals the benefits of traps may outweigh their risks. In addition, we discovered that the effects of combining two stressors do not result in the addition of the response originated by each factor separately.

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

Simple Summary

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

Abstract

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

Support vector machines for explaining physiological stress response in Wood mice (Apodemus sylvaticus)

Physiological stress response is a crucial adaptive mechanism for prey species survival. This paper aims to identify the main environmental and/or individual factors better explaining the stress response in Wood mice, Apodemus sylvaticus. We analyzed alterations in fecal glucocorticoid metabolite (FCM) concentration - extensively used as an accurate measure of the physiological stress response - of wild mice fecal samples seasonally collected during three years. Then, support vector machines were built to predict said concentration according to different stressors. These statistical tools appear to be particularly suitable for small datasets with substantial number of dimensions, corroborating that the stress response is an extremely complex process in which multiple factors can simultaneously partake in a context-dependent manner, i.e., the role of each potential stressor varies in time depending on other stressors. However, air-humidity, temperature and body-weight allowed us to explain the FCM fluctuation in 98% of our samples. The relevance of air-humidity and temperature altering FCM level could be linked to the presence of an abundant vegetation cover and, therefore, to food availability and predation risk perception. Body-weight might be related to the stress produced by reproduction and other intraspecific relationships such as social dominance or territorial behavior.

Hormones, stress and the welfare of animals

There are numerous endocrine (hormonal) responses during stress and these are often complex. This complexity makes the study of endocrine stress responses challenging and the challenges are intensified when attempts are made to use measures of hormones to assess the welfare of animals because so many endocrine systems are activated during stress and because there are countless stimuli that trigger these systems. Most research has concentrated on only a small number of these endocrine systems, particularly the hypothalamo–pituitary adrenal axis and the sympathoadrenal system, and there is a need to broaden the scope of endocrine systems that are studied. Furthermore, systematic approaches are required to establish when the actions of hormones associated with stress responses result in physiological and/or behavioural consequences that will have negative or positive effects on the welfare of animals.

Quantifying corticosterone in feathers: validations for an emerging technique

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

Within-sample variation in snowshoe hare faecal glucocorticoid metabolite measurements

Faecal glucocorticoid metabolite (FGM) concentrations are used increasingly as a non-invasive measure to index physiological stress experienced by diverse taxa. However, FGM may not be evenly distributed throughout a faecal mass or faecal pellet group. Moreover, within-sample variation in FGM measurements associated with different sampling and/or processing techniques is rarely reported despite potentially having important implications for inferring stress levels in free-ranging wildlife. Using a captive collection of snowshoe hares (Lepus americanus), we (i) assessed repeatability of FGM measurements (i.e. precision) from two processing techniques (measurements derived from dividing whole pellet groups into equal proportions prior to processing [G1], measurements from subsamples derived from thoroughly homogenized whole pellet groups [G2]) and (ii) conducted a power analysis to estimate sample-size requirements for detecting statistically significant differences in FGM concentrations at a population level. Our results indicate that the mean percent coefficient of variation (%CV) for within-sample FGM variation was slightly higher for G1 (%CV = 35, range 13.45-65.37) than for G2 (%CV = 23, range 7.26-47.94), though not statistically significant (two sample t-test, n = 8, t = 1.57, P = 0.16). Thus, FGM is relatively evenly distributed within snowshoe hare faecal pellet groups. However, subsampling from homogenized whole pellet groups may be more appropriate when the sampling time frame is less controlled (e.g. multiple defecation events) because a subsample derived from a homogenized whole pellet group might be more representative of the animal's 'average' physiological state compared to FGM concentrations derived from a few haphazardly selected faecal pellets. Power analysis results demonstrated the importance of a priori consideration of sample sizes. Relatively small effect sizes (e.g. <20%) may require sampling that is logistically and/or cost prohibitive. Yet for many situations of ecological or conservation interest, treatment effects may be substantial (>25%) and thus moderate sample sizes may be sufficient for testing research hypotheses regarding changes FGM concentrations.

Nest cover and faecal glucocorticoid metabolites are linked to hatching success and telomere length in breeding Common Eiders (Somateria mollissima)

Habitat-associated crypsis may affect perceived predation vulnerability, selecting for different predator avoidance strategies. Glucocorticoids could mediate the adjustment of escape responses to the extent of crypsis, introducing an overlooked source of variation in glucocorticoid–fitness relationships. However, prolonged exposure to elevated glucocorticoids may be costly, leading to accelerated telomere loss and, consequently, senescence. Here, we examined how nest cover and immunoreactive faecal glucocorticoid metabolite (fGCM) levels are linked to hatching success and telomere length in breeding female Common Eiders (Somateria mollissima (L., 1758)). We hypothesized that the degree of nest crypsis, reflecting differences in perceived predation risk, would moderate the relationship between reproductive success and fGCM levels. We also expected that telomere length would be shorter in birds with higher glucocorticoid concentration. Results showed that individuals with high fGCM levels had higher hatching success in nests with low cover, while low fGCM levels were more successful in well-concealed nests. We found that shorter telomeres were associated with high fGCM in nesting sites offering little cover and with low fGCM in well-concealed ones. This study provides the first evidence of habitat-dependent moderation of the relationships between stress physiology, telomere length and hatching success.

Diel pattern of corticosterone metabolites in Arctic barnacle goslings (Branta leucopsis) under continuous natural light

Here we describe the excretion pattern of corticosterone metabolites collected from droppings in barnacle goslings (Branta leucopsis) raised under 24 hours of continuous natural light in the Arctic. In lower latitudes, circulating corticosterone peaks around waking and shows a nadir between midnight and 4:00, whereas the peak and nadir are time-delayed slightly when measuring corticosterone metabolites from droppings. Photoperiod, along with other environmental factors, helps to entrain an animal's endogenous rhythm to that of the natural world. North of the Arctic Circle, photoperiod may not be a reliable cue as light is continuously absent during the winter and continuously present during the summer. Here, for the first time, we used droppings to describe a 24-hour excretion pattern of corticosterone metabolites (CORTm). By applying circular statistics for dependent data, we found a diel rhythmic pattern even under continuous natural light. We discuss potential alternative 'Zeitgeber' that may function even in the polar regions, focusing on melatonin. We propose a line of research to measure melatonin non-invasively from droppings. We also provide a validation of the adopted enzyme immunoassay (EIA) that was originally developed for greylag geese.

Non-invasive monitoring of physiological markers in primates

The monitoring of endocrine markers that inform about an animal's physiological state has become an invaluable tool for studying the behavioral ecology of primates. While the collection of blood samples usually requires the animal to be caught and immobilized, non-invasively collected samples of saliva, urine, feces or hair can be obtained without any major disturbance of the subject of interest. Such samples enable repeated collection which is required for matching behavioral information over long time periods with detailed information on endocrine markers. We start our review by giving an overview of endocrine and immune markers that have been successfully monitored in relation to topics of interest in primate behavioral ecology. These topics include reproductive, nutritional and health status, changes during ontogeny, social behavior such as rank relationships, aggression and cooperation as well as welfare and conservation issues. We continue by explaining which hormones can be measured in which matrices, and potential problems with measurements. We then describe different methods of hormone measurements and address their advantages and disadvantages. We finally emphasize the importance of thorough validation procedures when measuring a specific hormone in a new species or matrix.

One size does not fit all: Monitoring faecal glucocorticoid metabolites in marsupials

Marsupial research, conservation, and management can benefit greatly from knowledge about glucocorticoid (GC) secretion patterns because GCs influence numerous aspects of physiology and play a crucial role in regulating an animal's response to stressors. Faecal glucocorticoid metabolites (FGM) offer a non-invasive tool for tracking changes in GCs over time. To date, there are relatively few validated assays for marsupials compared with other taxa, and those that have been published generally test only one assay. However, different assays can yield very different signals of adrenal activity. The goal of this study was to compare the performance of five different enzyme immunoassays (EIAs) for monitoring adrenocortical activity via FGM in 13 marsupial species. We monitored FGM response to two types of events: biological stressors (e.g., transport, novel environment) and pharmacological stimulation (ACTH injection). For each individual animal and assay, FGM peaks were identified using the iterative baseline approach. Performance of the EIAs for each species was evaluated by determining (1) the percent of individuals with a detectable peak 0.125-4.5days post-event, and (2) the biological sensitivity of the assay as measured by strength of the post-event response relative to baseline variability (Z-score). Assays were defined as successful if they detected a peak in at least 50% of the individuals and the mean species response had a Z⩾2. By this criterion, at least one assay was successful in 10 of the 13 species, but the best-performing assay varied among species, even those species that were closely related. Furthermore, the ability to confidently assess assay performance was influenced by the experimental protocols used. We discuss the implications of our findings for biological validation studies.

Excretion and measurement of corticosterone and testosterone metabolites in bank voles (Myodes glareolus)

The bank vole is a commonly used model species in behavioral and ecophysiological studies. Thus, presenting a validated method for noninvasive monitoring of corticosterone and testosterone secretion is of high relevance. Here, we evaluated the effect of time of day and an ACTH challenge test on measured fecal corticosterone (FCM) and testosterone (FTM) metabolites in both sexes. Furthermore, we performed radiometabolism experiments for both steroids and sexes to study metabolism and excretion of ³H-corticosterone and ³H-testosterone. FCM and FTM were analysed with a 5α-pregnane-3β,11β,21-triol-20-one enzyme immunoassay (EIA) and a testosterone (measuring 17β-hydroxyandrostanes) EIA, respectively. Males had significantly higher FCM levels than females and their main excretion route was via the feces (∼72%), whereas females excreted nearly equal portions in both feces and urine. For testosterone the main excretion route was via the feces in both sexes (∼80%). The time course of excretion was similar in both sexes, but for the first time a significant difference between injected steroids was found: Corticosterone was excreted faster than testosterone, both in urine (median of peak levels: 4h vs 6h) and feces (6h vs 8h). Several metabolites were present in the feces and the tested EIAs reacted with some of them. Time of day had a significant effect on measured fecal steroid metabolites. As expected, males had significantly higher FTM levels than females. ACTH administration significantly increased FCM values; peaks were observed 4-8h after injection. In conclusion, both tested EIAs proved suited for a noninvasive measurement of glucocorticoids and androgens in bank voles.

Effect of weather conditions and presence of visitors on adrenocortical activity in captive African penguins (Spheniscus demersus)

A number of potential stressors are present in captive environments and it is critically important to identify them in order to improve health and welfare in ex situ animal populations. In this study, we investigated the adrenocortical activity of a colony of African penguins hosted in an immersive zoo in Italy, with respect to the presence of visitors and local microclimatic conditions, using the non-invasive method of assessing faecal glucocorticoid metabolites (FGMs). The penguins' exhibit is a large naturalistic outdoor enclosure, which closely reproduces the natural habitat of this species. Data collection took place from the beginning of June to the end of August 2014, during the period of maximum flow of visitors. We carried out 12 sampling periods, each involving 2 consecutive days; during the first day we counted the visitors and we registered the meteorological data, and on the second day, we collected the faecal samples, which amounted to a total of 285 faecal samples. Our results showed that the number of visitors did not influence the adrenocortical activity of the African penguins. Conversely, the local microclimatic conditions did influence the physiological stress on these birds. We found that an increase of the daily mean temperature induced a significant increase in FGM concentrations, although humidity and wind speed had a moderating effect on temperature and reduced the heat-induced stress. Moreover, we calculated two climatic indices, commonly used to assess the thermal discomfort in animals, namely the THI (Temperature-Humidity Index) and WCI (Wind Chill Index), and we detected a positive relationship between their values and the FGM levels, demonstrating that these indices could be useful indicators of weather discomfort in African penguins. Our study shows that the simulating naturalistic conditions could have significant benefits for zoo animals, such as reducing the negative effect of visitors. Nevertheless, it should be taken into account where the zoological facility is located and if the local microclimatic conditions are compatible with the hosted species, to ensure that they do not differ greatly from their natural habitat.

Circadian Rhythm and Stress Response in Droppings of Serinus canaria

Serinus canaria is a widespread domestic ornamental songbird, whose limited knowledge of biology make compelling studies aimed to monitor stress. Here, a commercial enzyme immunoassay was adopted to measure immunoreactive corticosterone (CORT) in single Serinus canaria dropping sample, to monitor the daily fecal excretion of CORT in birds bred singly or in-group and to detect the effect promoted by aviary or small transport cage restraint. A robust daily rhythm of CORT was recorded in animals held on short-day light cycle, independent of bred conditions (single or group), which persisted when space availability was modified in single bred animal (transfer in aviary and transport cages). By contrast, a significant change in CORT excretion was recorded when group bred animals are restrained in a smaller cage. The daily rhythm in CORT excretion in response to manipulation showed the greatest response at the beginning of the light period, followed by the absence of the peak usually recorded at the end of the dark phase. These data indicated that EIA could be used as a reliable noninvasive approach to monitor the stress induced by restraint conditions in Serinus canaria.

The Ecology of Stress: linking life-history traits with physiological control mechanisms in free-living guanacos

BACKGROUND

Providing the context for the evolution of life-history traits, habitat features constrain successful ecological and physiological strategies. In vertebrates, a key response to life's challenges is the activation of the Stress (HPA) and Gonadal (HPG) axes. Much of the interest in stress ecology is motivated by the desire to understand the physiological mechanisms in which the environment affects fitness. As reported in the literature, several intrinsic and extrinsic factors affect variability in hormone levels. In both social and non-social animals, the frequency and type of interaction with conspecifics, as well as the status in social species, can affect HPA axis activity, resulting in changes in the reproductive success of animals. We predicted that a social environment can affect both guanaco axes by increasing the secretion of testosterone (T) and Glucocorticoid (GCs) in response to individual social interactions and the energetic demands of breeding. Assuming that prolonged elevated levels of GCs over time can be harmful to individuals, it is predicted that the HPA axis suppresses the HPG axis and causes T levels to decrease, as GCs increase.

METHODS

All of the data for individuals were collected by non-invasive methods (fecal samples) to address hormonal activities. This is a novel approach in physiological ecology because feces are easily obtained through non-invasive sampling in animal populations.

RESULTS

As expected, there was a marked adrenal (p-value = .3.4e-12) and gonadal (p-value = 0.002656) response due to seasonal variation in Lama guanicoe. No significant differences were found in fecal GCs metabolites between males/females*season for the entire study period (p-value = 0.2839). Despite the seasonal activity variation in the hormonal profiles, our results show a positive correlation (p-value = 1.952e-11, COR = 0.50) between the adrenal and gonadal system. The marked endocrine (r2 = 0.806) and gonad (r2 = 0.7231) response due to seasonal variation in male guanaco individuals highlights the individual's energetic demands according to life-history strategies. This is a remarkable result because no inhibition was found between the axes as theory suggests. Finally, the dataset was used to build a reactive scope model for guanacos.

DISCUSSION

Guanacos cope with the trade-off between sociability and reproductive benefits and costs, by regulating their GCs and T levels on a seasonal basis, suggesting an adaptive role of both axes to different habitat pressures. The results presented here highlight the functional role of stress and gonad axes on a critical phase of a male mammal's life-the mating period-when all of the resources are at the disposal of the male and must be used to maximize the chances for reproductive success.

Non-invasive assessment of adrenocortical activity as a measure of stress in giraffe (Giraffa camelopardalis)

Background

Numbers of giraffes are declining rapidly in their native habitat. As giraffe research and conservation efforts increase, the demand for more complete measures of the impact of conservation interventions and the effects of captive environments on animal health and welfare have risen. We compared the ability of six different enzyme immunoassays to quantify changes in fecal glucocorticoid metabolites (FGM) resulting from three sources: adrenocorticotropic hormone stimulation test, transport, and time of day that samples were collected.

Results

Two male giraffes underwent ACTH injections; all six assays detected FGM increases following injection for Giraffe 1, while only three assays detected FGM increases following injection for Giraffe 2. Consistent with other ruminant species, the two 11-oxoetiocholanolone assays (one for 11,17-dioxoandrostanes and the other for 3α,11-oxo metabolites) measured the most pronounced and prolonged elevation of FGM, while an assay for 3β,11β-diol detected peaks of smaller magnitude and duration. Both of the 11-oxoetiocholanolone assays detected significant FGM increases after transport in Giraffes 3–7, and preliminary data suggest FGM detected by the assay for 11,17-dioxoandrostanes may differ across time of day.

Conclusions

We conclude the assay for 11,17-dioxoandrostanes is the most sensitive assay tested for FGM in giraffes and the assay for FGM with a 5β-3α-ol-11-one structure is also effective. 11-oxoetiocholanolone enzyme immunoassays have now been demonstrated to be successful in a wide variety of ruminant species, providing indirect evidence that 5β-reduction may be a common metabolic pathway for glucocorticoids in ruminants. As FGM peaks were detected in at least some giraffes using all assays tested, giraffes appear to excrete a wide variety of different FGM. The assays validated here will provide a valuable tool for research on the health, welfare, and conservation of giraffes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0864-8) contains supplementary material, which is available to authorized users.

An association between feather damaging behavior and corticosterone metabolite excretion in captive African grey parrots (Psittacus erithacus)

Background

African grey parrots (Psittacus erithacus) are kept as pets and are frequently hand-reared. It has been observed that hand-reared African grey parrots may develop behavioral disorders such as feather damaging behavior (FDB). It is well known that chronic stress is involved in behavioral disorders in captive parrots. The main glucocorticoid in birds is corticosterone; its quantification provides information about adrenocortical activity and is considered to be a reliable indicator of stress levels in birds. We analyzed the differences in the excretion of corticosterone metabolites (CM) in the droppings of African grey parrots characterized by: 1. different rearing histories (parent rearing vs. hand rearing); and 2. the presence or absence of FDB in hand-reared parrots.

Methods

A total of 82 African grey parrots that were kept in captivity were considered. According to breeding methods, three groups of birds were defined: 1. The parent-reared (PR) parrots included birds kept in pairs (n = 30 pairs) with a conspecific partner of the opposite sex. All of these birds were healthy and never showed FDB signs; 2. The healthy hand-reared parrots (H-HR) included pet parrots individually kept, that were hand-reared and did not display any sign of FDB (n = 11, 7 males and 4 females); 3. The FDB hand-reared parrot (FDB-HR) included pet parrots individually kept, that were hand-reared and displayed FDB (n = 11, 7 males and 4 females). Droppings were collected in the morning over three alternating days in autumn 2014 and spring 2015. The CM were determined using a multi-species corticosterone enzyme immunoassay kit. Split-plot repeated-measure ANOVA was used to examine any differences using group, season and group × season as the main factors.

Results

Different quantities of CM in droppings were found for the three groups. The mean CM value was 587 ng/g in the PR parrots, 494 ng/g in the H-HR parrots and 1,744 ng/g in the FDB-HR parrots, irrespective of the season. The excretion of CM in FDB-HR was significantly higher than in PR or H-HR parrots. CM in droppings were not influenced by the season (autumn vs. spring); furthermore, the interaction between group and sampling season was not significant. Limited to the H-HR and FDB-HR groups, a trend in the significance of the difference in the mean CM excreted by male and female birds was observed, with the levels excreted by males being higher than those excreted by females. When the effect of age was considered (in the two separate groups), there was a statistically significant positive correlation only for H-HR.

Conclusions

The highest amount of CM excretion was found in FDB-HR parrots, and a positive correlation between age and CM excretion was found in H-HR. Given that the CM excretion of both PR and H-HR parrots was similar in our study, future research is recommended to investigate the specific aspects of hand-rearing to improve parrot welfare.

Validating faecal glucocorticoid metabolite analysis in the Virunga mountain gorilla using a natural biological stressor

The continued degradation of primate habitat worldwide is forcing many primate populations into small protected forest islands surrounded by high-density human populations. One well-studied example is the critically endangered mountain gorilla (Gorilla beringei beringei). Decades of monitoring and research on Rwanda's mountain gorillas offer a unique opportunity to use non-invasive endocrine analysis to address pressing questions about the conservation of this endangered population. The aims of our study were as follows: (i) to validate field and laboratory methods for assessing stress through faecal glucocorticoid metabolite (FGM) analysis using inter-social unit interactions as a natural stressor; (ii) to determine the excretion lag times between interactions and detectable stress response in faeces; and (iii) to determine whether there are circadian patterns of FGM excretion. We collected ~6000 faecal samples from 127 known gorillas in 10 habituated groups, monitored by the Dian Fossey Gorilla Fund's Karisoke Research Center over 21 months in 2011 and 2012. Extracted FGMs were measured using a cortisol enzyme immunoassay (R4866; C. J. Munro). Results revealed cause-effect relationships between inter-unit interactions and increased FGMs (relative to individual pre-event samples) between 20 and 140 h after interactions, with the peak most often occurring on day 3. There was no evidence of circadian patterns in FGM concentrations, as previously shown in many species with long gut passage times. However, baseline FGM concentrations were lower in adult males than in adult females, and variation was associated with the collection month, indicating possible seasonal variation. This study provides a biologically validated, field-friendly faecal hormone metabolite extraction and laboratory enzyme immunoassay analysis method for non-invasive monitoring of adrenocortical activity in Virunga mountain gorillas. The methods are useful for future evaluation of a variety of environmental and human-induced potential stressors in this critically endangered population.

Stress assessment in captive greylag geese (Anser anser)

Chronic stress--or, more appropriately, "allostatic overload"--may be physiologically harmful and can cause death in the most severe cases. Animals in captivity are thought to be particularly vulnerable to allostatic overload due to artificial housing and group makeup. Here we attempted to determine if captive greylag geese (Anser anser), housed lifelong in captivity, showed elevated levels of immunoreactive corticosterone metabolites (CORT) and ectoparasites in dropping samples as well as some hematological parameters (hematocrit, packed cell volume, total white blood cell count [TWBC], and heterophil:lymphocyte ratio [H:L]). All of these have been measured as indicators of chronic stress. Furthermore, we correlated the various stress parameters within individuals. Captive geese showed elevated values of CORT and ectoparasites relative to a wild population sampled in the vicinity of the area where the captive flock is held. The elevated levels, however, were by no means at a pathological level and fall well into the range of other published values in wild greylag geese. We found no correlations between any of the variables measured from droppings with any of the ones collected from blood. Among the blood parameters, only the H:L negatively correlated with TWBC. We examine the problem of inferring allostatic overload when measuring only 1 stress parameter, as there is no consistency between various measurements taken. We discuss the different aspects of each of the parameters measured and the extensive individual variation in response to stress as well as the timing at which different systems respond to a stressor and what is actually measured at the time of data collection. We conclude that measuring only 1 stress parameter often is insufficient to evaluate the well-being of both wild and captively housed animals and that collecting behavioral data on stress might be a suitable addition.

Effects of population density on corticosterone levels of prairie voles in the field

High population density is often associated with increased levels of stress-related hormones, such as corticosterone (CORT). Prairie voles (Microtus ochrogaster) are a socially monogamous species known for their large population density fluctuations in the wild. Although CORT influences the social behavior of prairie voles in the lab, the effect of population density on CORT has not previously been quantified in this species in the field. We validated a non-invasive hormone assay for measuring CORT metabolites in prairie vole feces. We then used semi-natural enclosures to experimentally manipulate population density, and measured density effects on male space use and fecal CORT levels. Our enclosures generated patterns of space use and social interaction that were consistent with previous prairie vole field studies. Contrary to the positive relationship between CORT and density typical of other taxa, we found that lower population densities (80 animals/ha) produced higher fecal CORT than higher densities (240/ha). Combined with prior work in the lab and field, the data suggest that high prairie vole population densities indicate favorable environments, perhaps through reduced predation risk. Lastly, we found that field animals had lower fecal CORT levels than laboratory-living animals. The data emphasize the usefulness of prairie voles as models for integrating ecological, evolutionary, and mechanistic questions in social behavior.

Non-Invasive Measurement of Adrenocortical Activity in Blue-Fronted Parrots (Amazona aestiva, Linnaeus, 1758)

Parrots kept in zoos and private households often develop psychological and behavioural disorders. Despite knowing that such disorders have a multifactorial aetiology and that chronic stress is involved, little is known about their development mainly due to a poor understanding of the parrots' physiology and the lack of validated methods to measure stress in these species. In birds, blood corticosterone concentrations provide information about adrenocortical activity. However, blood sampling techniques are difficult, highly invasive and inappropriate to investigate stressful situations and welfare conditions. Thus, a non-invasive method to measure steroid hormones is critically needed. Aiming to perform a physiological validation of a cortisone enzyme immunoassay (EIA) to measure glucocorticoid metabolites (GCM) in droppings of 24 Blue-fronted parrots (Amazona aestiva), two experiments were designed. During the experiments all droppings were collected at 3-h intervals. Initially, birds were sampled for 24 h (experiment 1) and one week later assigned to four different treatments (experiment 2): Control (undisturbed), Saline (0.2 mL of 0.9% NaCl IM), Dexamethasone (1 mg/kg IM) and Adrenocorticotropic hormone (ACTH; 25 IU IM). Treatments (always one week apart) were applied to all animals in a cross-over study design. A daily rhythm pattern in GCM excretion was detected but there were no sex differences (first experiment). Saline and dexamethasone treatments had no effect on GCM (not different from control concentrations). Following ACTH injection, GCM concentration increased about 13.1-fold (median) at the peak (after 3-9 h), and then dropped to pre-treatment concentrations. By a successful physiological validation, we demonstrated the suitability of the cortisone EIA to non-invasively monitor increased adrenocortical activity, and thus, stress in the Blue-fronted parrot. This method opens up new perspectives for investigating the connection between behavioural disorders and stress in this bird species, and could also help in their captive management.

Non-invasive monitoring of adrenocortical activity in captive African Penguin (Spheniscus demersus) by measuring faecal glucocorticoid metabolites

Measurement of faecal glucocorticoid metabolites (FGMs) has become a useful and widely-accepted method for the non-invasive evaluation of stress in vertebrates. In this study we assessed the adrenocortical activity of five captive African Penguins (Spheniscus demersus) by means of FGM evaluation following a biological stressor, i.e. capture and immobilization. In addition, we detected individual differences in secretion of FGMs during a stage of the normal biological cycle of penguins, namely the breeding period, without any external or induced causes of stress. Our results showed that FGM concentrations peaked 5.5-8h after the induced stress in all birds, and significantly decreased within 30 h. As predictable, the highest peak of FGMs (6591 ng/g) was reached by the youngest penguin, which was at its first experience with the stressor. This peak was 1.8-2.7-fold higher compared to those of the other animals habituated to the stimulus. For the breeding period, our results revealed that the increase in FGMs compared to ordinary levels, and the peaks of FGMs, varied widely depending on the age and mainly on the reproductive state of the animal. The bird which showed the lowest peak (2518 ng/g) was an old male that was not in a reproductive state at the time of the study. Higher FGM increases and peaks were reached by the two birds which were brooding (male: 5552%, 96,631 ng/g; female: 1438%, 22,846 ng/g) and by the youngest bird (1582%, 39,700 ng/g). The impact of the reproductive state on FGM levels was unexpected compared to that produced by the induced stress. The EIA used in this study to measure FGM levels proved to be a reliable tool for assessing individual and biologically-relevant changes in FGM concentrations in African Penguin. Moreover, this method allowed detection of physiological stress during the breeding period, and identification of individual differences in relation to the reproductive status. The increase in FGM levels as a response to capture and immobilization suggests that the measured metabolites are appropriate indicators of adrenal activity in these birds.

Environmental and Intrinsic Correlates of Stress in Free-Ranging Wolves

BACKGROUND

When confronted with a stressor, animals react with several physiological and behavioral responses. Although sustained or repeated stress can result in severe deleterious physiological effects, the causes of stress in free-ranging animals are yet poorly documented. In our study, we aimed at identifying the main factors affecting stress levels in free-ranging wolves (Canis lupus).

METHODOLOGY/PRINCIPAL FINDINGS

We used fecal cortisol metabolites (FCM) as an index of stress, after validating the method for its application in wolves. We analyzed a total of 450 fecal samples from eleven wolf packs belonging to three protected populations, in Italy (Abruzzo), France (Mercantour), and the United States (Yellowstone). We collected samples during two consecutive winters in each study area. We found no relationship between FCM concentrations and age, sex or social status of individuals. At the group level, our results suggest that breeding pair permanency and the loss of pack members through processes different from dispersal may importantly impact stress levels in wolves. We measured higher FCM levels in comparatively small packs living in sympatry with a population of free-ranging dogs. Lastly, our results indicate that FCM concentrations are associated with endoparasitic infections of individuals.

CONCLUSIONS/SIGNIFICANCE

In social mammals sharing strong bonds among group members, the death of one or several members of the group most likely induces important stress in the remainder of the social unit. The potential impact of social and territorial stability on stress levels should be further investigated in free-ranging populations, especially in highly social and in territorial species. As persistent or repeated stressors may facilitate or induce pathologies and physiological alterations that can affect survival and fitness, we advocate considering the potential impact of anthropogenic causes of stress in management and conservation programs regarding wolves and other wildlife.