Losing seasonal patterns in a hibernating omnivore? Diet quality proxies and faecal cortisol metabolites in brown bears in areas with and without artificial feeding.

Agnieszka Sergiel,Álvaro Navarro-Castilla,Tomasz Zwijacz-Kozica,Isabel Barja,Nuria Selva,Nicoletta Righini

doi:10.1371/journal.pone.0242341

Abstract

Bears are omnivores particularly well-adapted to variations in the nutritional composition, quality and availability of food resources. Artificial feeding practices have been shown to strongly influence diet composition and seasonality, as well as to cause alterations in wintering and movement in brown bears (Ursus arctos). In this study, we investigated seasonal differences (hypophagia vs hyperphagia) in food quality of two brown bear subpopulations in the Polish Carpathians using faecal nitrogen (FN) and carbon (FC) estimates. The subpopulations inhabit areas that differ in artificial feeding practices: no artificial feeding occurs in the western subpopulation (Tatra Mountains), while artificial food targeted to ungulates is provided and used year-round in the eastern subpopulation (Bieszczady Mountains). We also compared these results with faecal cortisol metabolites (FCM) to explore how FN and FC correlate with the hypothalamic-pituitary-adrenal axis activity and if the seasonal patterns are apparent. We found that in Tatra Mts bears fed on significantly higher quality diet, as shown by FN and FC values, and had significantly higher FC levels in hyperphagia, when they accumulate fat reserves for wintering. The pattern in FCM levels for Tatra subpopulation followed the changes in energy intake during the seasons of hypo- and hyperphagia, while in Bieszczady Mts, the area with intensive feeding, no seasonal patterns could be observed. Artificial feeding practices may disrupt nutrient phenology and seasonality, relative to subpopulations with natural diets. We showed that the availability of human-provided foods may alter not only the overall dietary quality, but also hormonal patterns linked to seasonal nutritional requirements. Combining FN, FC and FCM proved to be a useful tool for reconstructing diet quality and related physiological patterns.

Highlights

An explicit evaluation of the nutritional parameters of an animal’s diet is essential to comprehend foraging patterns in different habitats and ecosystems [1,2]
Using the brown bear as a model species of a seasonal mammal, we investigated whether the association between diet quality proxies (FN, faecal carbon (FC)) and glucocorticoids levels (FCM) and their seasonal patterns are affected by artificial feeding practices
We examined seasonal variation in faecal nitrogen (FN), FC and faecal cortisol metabolites (FCM) in the two core areas of the brown bear population in the Polish Carpathians, which differ in the management practices regarding artificial feeding

Summary

Introduction

An explicit evaluation of the nutritional parameters of an animal’s diet is essential to comprehend foraging patterns in different habitats and ecosystems [1,2]. Faeces are the most accessible biological product from wildlife in nature, and their analysis is one of the most commonly used techniques for assessing food habits and dietary quality in mammals [3,4,5,6]. These studies are no longer limited to the identification of undigested food remains. The percentage of nitrogen content in faeces represents the protein content of the food consumed, and, it is considered as a biomarker for diet quality and shifts in diet composition [7,8,13,18], while faecal carbon (FC) indicates changes in energy consumption and shifts in energy intake from digested food items [7]

Methods

Results

Conclusion