Maximizing the reliability of non-invasive endocrine sampling in the tiger (Panthera tigris): environmental decay and intra-sample variation in faecal glucocorticoid metabolites

Novel frontier in wildlife monitoring: Identification of small rodent species from fecal pellets using near-infrared reflectance spectroscopy (NIRS)

Small rodents are prevalent and functionally important across the world's biomes, making their monitoring salient for ecosystem management, conservation, forestry, and agriculture. There is a growing need for cost-effective and noninvasive methods for large-scale, intensive sampling. Fecal pellet counts readily provide relative abundance indices, and given suitable analytical methods, feces could also allow for the determination of multiple ecological and physiological variables, including community composition. In this context, we developed calibration models for rodent taxonomic determination using fecal near-infrared reflectance spectroscopy (fNIRS). Our results demonstrate fNIRS as an accurate and robust method for predicting genus and species identity of five coexisting subarctic microtine rodent species. We show that sample exposure to weathering increases the method's accuracy, indicating its suitability for samples collected from the field. Diet was not a major determinant of species prediction accuracy in our samples, as diet exhibited large variation and overlap between species. fNIRS could also be applied across regions, as calibration models including samples from two regions provided a good prediction accuracy for both regions. We show fNIRS as a fast and cost-efficient high-throughput method for rodent taxonomic determination, with the potential for cross-regional calibrations and the use on field-collected samples. Importantly, appeal lies in the versatility of fNIRS. In addition to rodent population censuses, fNIRS can provide information on demography, fecal nutrients, stress hormones, and even disease. Given the development of such calibration models, fNIRS analytics could complement novel genetic methods and greatly support ecosystem- and interaction-based approaches to monitoring.

Temporal stability of fecal cortisol metabolites in mountain-dwelling ungulates

Fecal cortisol metabolites (FCMs) are widely used to track stress responses in wildlife and captive species. Rules of thumb suggest that samples should be collected as soon as possible after defecation, to avoid decay of FCMs. To date, however, only a few studies investigated the stability of defecated FCMs over time, and most of them were conducted in controlled laboratory conditions. Here, we investigated the stability of FCMs over seven consecutive days, in two mountain-dwelling ungulates, under natural environmental conditions using a semi-experimental approach. Fecal samples from Northern chamois Rupicapra rupicapra (n = 24) and red deer Cervus elaphus (n = 22) were collected in summer of 2020 within the Stelvio National Park, Italy, and placed in an open area above 2000 m a.s.l. For the next 7 days, we collected a portion of each sample, and all sub-samples were analyzed with an 11-oxoetiocholanolone enzyme immunoassay. Exposure, temperature, and precipitation were fitted as covariates in non-linear generalized mixed models to assess FCM variation over time, and competing models were selected using AICc. For chamois, the best model included only time as a predictor, while for red deer, it included time, precipitation, and exposure. For both species, FCM values decreased rapidly from the first days after deposition until the fourth day. For red deer, in northern-exposed samples, FCM values decreased slower than in south-exposed ones; furthermore, FCM values increased with increasing precipitation. Our results offer a solid methodological basis to wildlife researchers and practitioners interested in the investigation of the ecological factors affecting stress variation in wildlife and support the recommendation to collect samples as fresh as possible, to avoid misleading inference. Further studies are necessary to evaluate the stability of FCMs when other enzyme immunoassays are used.

Non-invasive monitoring of glucocorticoid metabolite concentrations in native Indian, as well as captive and re-wilded tigers in South Africa

Over the last century, wild tiger (Panthera tigris) numbers have declined from over 100 000 individuals to fewer than 4 000, with animals now confined to less than 5% of their historic range due to habitat loss, persecution, inadequate management, and poaching. In contrast, 15 000-20 000 tigers are estimated to be housed in captivity, experiencing conditions vastly different than their wild counterparts. A total of 280 tigers are currently held at 44 different facilities within South Africa, including zoos, semi-captive 're-wilded' populations, and pets; these animals provide a unique opportunity to measure the impact of extrinsic factors, found in exotic habitats, on the adrenocortical activity of tigers. By monitoring and comparing stress-related faecal glucocorticoid metabolite (fGCM) concentrations of tigers housed at different locations, and free ranging tigers in natural tiger reserves, this project aimed to get a better understanding of the impact of extrinsic factors on adrenocortical function as a measure of stress. The results of this study showed no significant difference in fGCM concentrations between captive, re-wilded, and free-ranging tigers with the exception of one site. Furthermore, factors such as sex and season were not significant drivers of fGCM concentrations. One study group had elevated fGCM concentrations, showing population variation in the stress response. This indicates that populations are able to cope with exotic environments, however, as population-specific differences in the stress response exist, we suggest management protocols be created for each population. This study offered the unique opportunity to see how well tigers are faring outside of their native range and if having re-wilded tigers in exotic locations is a potential welfare-acceptable management option for tiger conservation globally.

Timed environmental exposure indicates sample stability for reliable noninvasive measurement of fecal cortisol metabolite concentrations in sheep

The use of noninvasive techniques to evaluate stress responses in animals has become an increasingly popular method of animal welfare assessment in both production animals and wildlife. In particular, using fecal samples to measure fecal cortisol metabolites (FCMs) as a quantitative measure has proven ideal as samples can be collected remote to the animal after defecation without the need for invasive procedures. Colorimetric enzyme immunoassays (EIAs) have been shown to have a high level of selectivity and sensitivity for FCM concentration analysis, equivalent to the traditionally used radioimmunoassay. Regardless of the assay system used, species- and sample-specific validation must be undertaken to ensure the reliability of results, particularly where sampling is undertaken in a novel species or where environmental conditions might impact FCM stability in the fecal sample. To determine the limit of environmental exposure acceptable for analysis of FCM concentrations in ovine scat samples collected from a paddock under conditions of stable heat and humidity, this study quantified FCMs in ovine feces shortly after defecation (2-7 h) and after timed environmental exposure (1-9 d). Samples were determined to show stable FCM concentrations for up to 5 d by this analysis. Understanding the impacts of environmental exposure, and therefore the viability of remote fecal collection methods for quantitative analysis of FCM by EIA, is important to assess the utility of noninvasive measures of endocrine status in animals where the exact timing of defecation may not be known.

No island-effect on glucocorticoid levels for a rodent from a near-shore archipelago

Island rodents are often larger and live at higher population densities than their mainland counterparts, characteristics that have been referred to as "island syndrome". Island syndrome has been well studied, but few studies have tested for island-mainland differences in stress physiology. We evaluated island syndrome within the context of stress physiology of white-footed mice (Peromyscus leucopus) captured from 11 islands and five mainland sites in Thousand Islands National Park, Ontario, Canada. Stress physiology was evaluated by quantifying corticosterone (a stress biomarker), the primary glucocorticoid in mice, from hair and its related metabolites from fecal samples. White-footed mice captured in this near-shore archipelago did not display characteristics of island syndrome, nor differences in levels of hair corticosterone or fecal corticosterone metabolites compared with mainland mice. We suggest that island white-footed mice experience similar degrees of stress in the Thousand Islands compared with the mainland. Although we did not find evidence of island syndrome or differences in glucocorticoid levels, we identified relationships between internal (sex, body mass) and external (season) factors and our hormonal indices of stress in white-footed mice.

Changes in the corticosterone level in tooting male black grouse (Tetrao tetrix) infected with Eimeria spp

The black grouse (Tetrao tetrix) is a forest bird species critically endangered of extinction. Enclosed aviary breeding is among the measures taken to protect the species. Complex factors can affect its reproduction success, including coccidiosis. In this article, corticosterone level (as a reliable biomarker of stress in birds) and prevalence of Eimeria spp. were determined in male black grouse kept in aviary breeding center before, during, and after the reproductive season (called tooting). The correlation between those parameters was also analyzed. The corticosterone level was measured with noninvasive method in fecal samples in an immunoassay. The prevalence of Eimeria spp. was determined by the qualitative (Fülleborn's flotation) and quantitative method (McMaster's method as modified by Raynaud). Results show the occurrence of 3 species of Eimeria spp. in males: Eimeria lyruri, Eimeria nadsoni, and Eimeria nonbrumpti. Infestation with E. lyruri was chronic in nature. A co-invasion of E. lyruri, E. nadsoni, and E. nonbrumpti was observed during (prevalence 60%) and after the tooting (prevalence 40%). The study showed no statistical changes in the oocysts per 1 g of feces (CORTl) and oocysts per 1 g of feces (OPG) in assays I-III and absence of correlation between CORTl and OPG. The results of this experiment do not support the hypothesis that chronic infestation with Eimeria spp. can induce chronic stress in grouse. But may suggest that males of black grouse are susceptible to infestation with other species of Eimeria spp. during mating season. The knowledge of the level of individual stress and parasitic infestation can be used to take protective actions for this bird species, especially to achieve higher survival rate and bird reproduction rate. Tangible effects will include an assessment of the relationship between individual susceptibility and chronic environmental stress caused by coccidia.

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.