DIET AND FORAGING BEHAVIOR

Bear Baiting   

Foods grown or manufactured by people (hereinafter, anthropogenic foods), including grains, livestock, and foodstuff, are often responsible for attracting wildlife to human use areas because these foods are high in nutritional value and often freely available (Fedriani et al. 2001). Results from past research suggests that animals that forage for anthropogenic foods are often larger (Graber 1982); have higher reproductive rates (Keay 1995); are distributed more densely (Fedriani et al. 2001; Jerina 2012; Stergar and Jerina 2017); seem bolder around people than conspecifics that forage for natural foods exclusively (Smith et al. 2005); and are often harvested by hunters or removed by wildlife managers because they are often involved in conflict with people and their property (Hopkins and Kalinowski 2013).

There are potential benefits and drawbacks to deliberately feeding wildlife (Kubasiewicz et al. 2015; Garshelis et al. 2017). In some areas, wildlife gain access to supplemental food sources or are baited intentionally to increase harvest rates (with bears: McLaughlin and Smith 1990), reproductive rates (Robb et al. 2008), and densities (Boutin 1990); to promote ecotourism (Orams 2002); facilitate monitoring of target species (Garshelis et al. 2017); and to divert animals from human-use areas or activities, reducing the potential for conflict with people and their property (Steyaert et al. 2014; Kubasiewicz et al. 2015, Kavčič et al., 2015). In other areas, feeding human-derived foods to wildlife is strictly prohibited because animals conditioned to forage for these food sources are often in conflict with people or their property.

To study the ecological effects of anthropogenic foods on wildlife, it is important to develop both appropriate field methods and quantitative tools. First, it is essential to detect individuals in populations that forage for anthropogenic foods and estimate their diets (e.g., Hopkins et al. 2012). Then, researchers can examine the effects of diet on the health, behavior, survival, and fecundity of bears that use anthropogenic foods and those that do not. Fecal analysis is a technique that is often used to measure the contribution of anthropogenic foods in the diets of animals; however, collecting and analyzing scats from a representative sample of a population can be expensive and time consuming; in addition, because human foods are often highly digestible, they are often underrepresented in scats and underestimated in calculations of percent volume (Hewitt and Robbins 1996).

Reconstructing the digestible diets of bears using naturally occurring stable isotopes is one of the greatest breakthroughs in the nutritional ecology of ursids in the past 20 years (Schwartz et al. 2014). The isotopic analysis of hair is particularly useful because stable isotopes from foods are preserved within its metabolically inert keratin structure (Schwertl et al. 2003), which can be used to investigate the diets of animals during the time it took hair to grow (whole hair analysis: Newsome et al. 2010; Hopkins et al. 2012, 2014a, 2014b; Bentzen 2014; Murray et al. 2015) or through time (segment analysis: Schwertl et al. 2003; Ayliffe et al. 2004; Mizukami et al. 2005; Hopkins and Kurle 2015; Ditmer et al. 2016).

Carbon (13C/12C, expressed as d13C values) and nitrogen (15N/14N, expressed as d15N values) stable isotope ratios in hair have been used to identify animals within a population that consumed anthropogenic foods because the isotopic signature of such human-derived foods and their natural counterparts are often isotopically different. For instance, relatively high d13C values measured in hair keratin of bears that occupy C3 landscapes often indicate consumption of C4 anthropogenic foods, such as corn- or sugar cane-derived human foodstuff (Mizukami et al. 2005; Hopkins et al. 2014b; Hopkins and Kurle 2015; Ditmer et al. 2016; Kirby et al. 2016, 2017). In addition, bears that foraged for meat-rich, anthropogenic foods, often exhibit higher d15N values in their hair than bears that primarily foraged for plants (Hopkins et al. 2012, 2014).

Nearly half of the northeastern states (47%) and provinces of North America use anthropogenic foods (e.g., corn, donuts, trail mix) as bait to lure black bears to locations where they are then harvested (Sawaya et al. 2013; Table 1). Currently, little is known about the impact of hunting bait on the health, behavior, and population dynamics of black bears. Detecting individual bears that rely on bait and understanding any impacts on their behavior or health outcomes is of particular interest to wildlife management agencies because baiting bears is currently the most successful method for harvesting bears in Maine and other states; however, there may be unintended consequences from baiting such as increased densities, range expansion, and increased conflict in certain areas. In this study, we investigate the diets of bears in Maine (especially those that feed on bait), and the consequences of different diets on individual growth, health, and vital rates of bears.