Effects of Sex and Age on Winter Diet of American Martens in Michigan

We investigated whether sex or age influenced winter diet in American martens (Martes americana) from the Upper Peninsula of Michigan by analyzing gut content of 151 individuals trapped during 2000–2004. We identified 433 occurrences of 10 prey species and classified them into six groups based on body size. Overall, marten diets were similar to those reported previously. Proportion of prey groups and kilocalories consumed were generally similar between male and female marten diets, as well as between juveniles and adults. Average dietary breadth (0.46) was comparatively high but within the range reported for other North American studies. Dietary overlap (0.99) was high between males and females and between juveniles and adults. Comparable diets between sexes suggest that size sexual dimorphism was unrelated to prey species consumed. Similarly, diets of juveniles and adults were comparable. Mice and voles occurred most frequently in marten diets; however, squirrels represented the greatest proportion of kilocalories consumed. Future studies of marten diet should emphasize prey abundance. OHIO J. SCI. 108 (4): 60-64, 2008 1Address correspondence to Jerrold l. Belant, Department of Wildlife and Fisheries, Mississippi State University, Box 9690, Starkville, MS 39762. Telephone: 662-3252996. Fax: 662-325-8795. E-mail: [email protected] INTRODUCTION Adult male American martens (Martes americana) are 20–40% heavier than females (Strickland et al. 1982, Buskirk and MacDonald 1989, Holmes and Powell 1994). Dimorphism of this magnitude would be expected to result in prey partitioning between sexes (Dayan and Simberloff 1994). However, several studies have reported high dietary overlap between male and female martens, suggesting little partitioning of prey species (Nagorsen et al. 1989, 1991; Andruskiw 2003). Where differences between male and female diets have been reported, males ate larger prey such as ruffed grouse (Bonasa umbellus) and snowshoe hares (Lepus americanus) while females most commonly consumed mice and voles (Poole and Graf 1996, Bull 2000). As animals mature, foraging skills are refined (Raven et al. 2005). Consequently, juveniles are generally considered less skilled hunters than adults which may be reflected in their diets. Few studies have compared juvenile (<1 year old) and adult (>1 year old) American marten diets and those results are conflicting. Thompson and Colgan (1987) found no differences between juvenile and adult diets in north central ontario. In contrast, juvenile martens in the Northwest Territories consumed more large prey items (e.g., snowshoe hare) than adults (Poole and Graf 1996). Because the influence of size and age on marten diet remains conflicting and no data on marten diet are available for Michigan, our objectives were to: 1) estimate marten diet in Michigan’s Upper Peninsula (UP) during early winter, and 2) compare diet by sex and age groups using frequency of occurrence and estimated caloric intake. MATERIAL AND METHODS The Upper Peninsula of Michigan is located on the southern shore of lake Superior and covers an area of 42,610 km2 (latitude: 45o45’–46o49’ N, longitude: 84o15’–89o30’ W). December temperatures ranged from average lows of -8° C to highs of -1° C; average precipitation during the study was 49.5 cm.