Abstract
Patch use can illustrate the contributions that forage quality and foraging risk make in shaping foraging decisions made under the risk of being killed. We aimed to determine whether forage selection by European bison Bison bonasus was state-dependent in being shaped by risk (wolf predation or human poaching/culling avoidance) or nutrient quality at two time periods—early winter (when resources are abundant) and at the end of winter (when resources are scarce)—in Białowieża Primeval Forest (Poland). We used a giving-up density framework using the proportional consumption of hay provided by humans to measure the perceptions of risk in European bison. European bison resource selection was primarily driven by minimising the distance they travel over open ground in early winter (i.e. avoiding humans), however by the end of winter, when resources are scarce, bison selected haystacks for their nutrient quality (low fibre, high Mg and energy). This study illustrates how resource selection varies according to the condition of animals (i.e. state-dependency affects the marginal value theorem). It also indicates conservation managers using hay quality may actively manage human–bison conflicts in trouble spots and that bison are currently free from top-down limitation in Białowieża as they do not perceive wolves as threatening enough to alter their foraging behaviour.
Highlights
Optimal foraging theory provides a framework for studying the perceptions of wildlife to the risks inherent in their environment (Brown 1988; Brown and Kotler 2004; Druce et al 2006)
AICc refers to Akaike’s Information Criteria, HRC refers to the distance to the home range centre and all variables are measured in km results, Akaike’s weights showed that proximity to forest was still the primary driver of which haystacks bison sampled by the end of winter with 19–48 % mPore support Pthan the otPher variables (P Forestwi = 0.79; EnergywiP= 0.64; NDFwi = 0.54; Home Range Centrewi = 0.52; Mgwi = 0.41)
There was no support for hypotheses 3 or 5. This giving-up densities (GUDs) study reveals that the perception of risk in an animal’s environment varies according to the condition of animals, that is, state-dependent behaviour clearly affects the marginal value theorem (Nonacs 2001)
Summary
Optimal foraging theory provides a framework for studying the perceptions of wildlife to the risks inherent in their environment (Brown 1988; Brown and Kotler 2004; Druce et al 2006). Measuring the use of foraging patches can reveal the costs and benefits of foraging for wildlife (Brown 1988). When harvest rates in a patch are a diminishing function of food density, giving-up densities (GUDs) are quantifiable and provide an estimate of foraging costs inter alia (Tadese and Kotler 2013). Diminishing returns in exploiting patches should drive foragers to exploit them until harvest rates decline to the level of the energetic, predation and missed opportunity costs of foraging (Brown 1988, 1992; Kotler et al 1994)
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