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Foods of American Badgers in West-central Minnesota and Southeastern North Dakota During the Duck Nesting Season

Methods


We obtained badger carcasses during April-July, mostly by trapping on Waterfowl Production Areas and occasional road kill in Becker, Grant and Ottertail counties of west-central Minnesota, and McIntosh and Stutsman counties of southeastern North Dakota [see Sargeant et al. (1995) for area description]. Topography of these counties is flat to gently rolling. Uplands were intensively farmed, primarily for small-grains, row crop and livestock. Grasslands consisted of pastures, hayland, wildlife management areas and lands enrolled in the Conservation Reserve Program (Bjerke, 1991). Wetland conditions were good for breeding ducks during 1987; nearly all wetlands were flooded. However, drought began that summer and by spring 1989 water remained only in semipermanent wetlands (Todhunter, 1995). Numbers of nesting waterfowl were high in 1987 and moderate during 1988-1990 (U.S. Fish and Wildlife Service and Canadian Wildlife Service, 1995).

We determined sex of badgers and estimated ages of adults (>1-y-old) using cementum analyses of canine teeth (Matson's Microtechnique, Inc. Milltown, MT). Badgers <6-mo-old (here after called juvenile) were easily identified without cementum analyses by their size and pelage. Reproductive status of females in the current year was determined from examination of reproductive tracts for embryos, placental scars or as evidenced by lactation. Gastrointestinal tracts were removed and frozen until contents were examined.

We removed and washed contents of each stomach and colon separately through a 36-mesh/cm2 sieve and dried the residues. Later we combined stomach and colon contents for individual animals, similar to methods of Messick and Hornocker (1981). Food items found in both stomach and colon were counted only once. We identified residues to the lowest taxon possible on the basis of hair, teeth, eggshell fragments, feathers, scales and exoskeletal parts using several methods, including reference collections. Hair was identified by microstructure (Adorjan and Kolenosky, 1969; Moore et al., 1974; Wallis, 1993); badger hair was excluded from analyses because we assumed it was ingested during grooming. Bird eggshell fragments were further separated based on color and thickness (Greenwood, 1981; Mallory and Weatherhead, 1990). We categorized eggshells 0.15 mm thick as passeriformes and other small species, >0.15 mm to <0.20 mm as medium-sized birds and 0.20 mm as duck eggs (Greenwood, 1981).

Residues of food items identified in gastrointestinal tracts are presented as percent frequency of occurrence. Plant residues are not included in analyses because, with exception of sunflower seeds, they occurred in small amounts and were probably ingested incidental to ingesting other foods. Ixodidae (wood tick) and Siphonoptera (flea) were excluded in analyses because they were always found as single individuals and were likely ingested during grooming.

Using chi-square analyses we compared frequencies of occurrence of animal foods by class for adult badgers between males and females and between seasons [spring (April-May) and summer (June-July)]. When expected values were <0.05, we used Fisher exact tests to evaluate variation in occurrence (Steel and Torrie, 1980). We did not include year as an explanatory variable in analyses because sample sizes were small. Likewise we excluded juvenile badgers from reported frequencies of occurrence and analyses because of small sample size. However, we provide information about diets of juvenile badgers because Messick et al. (1981) and Errington (1937) suggested there were differences in food habits of juvenile vs. adult badgers.


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