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Monday, February 6 • 4:00pm - 4:20pm
Technical Session. Factors Correlated with Declining Antler Diameters of Yearling Deer in Michigan

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AUTHORS: Gary J. Roloff, Michigan State University; Sean Sultaire, Michigan State University; Brent Rudolph, Michigan Department of Natural Resources, Rebecca Cain, Michigan State University

ABSTRACT: Long-term declines in antler sizes of white-tailed deer can indicate reduced habitat quality, sub-optimal herd demographics, or inferior genetics. The Michigan Department of Natural Resources used a standardized technique to measure antler base diameters of deer brought to check stations.  Records from 127,032 yearling deer harvested in 39 southern Michigan counties from 1980 – 2015 indicated a statistically significant 35-year decline in yearling deer antler diameters (β126,992 = -0.023, t = -16.11, p < 0.001). We sought to understand habitat, climate, and herd variables correlated with the decline across this study area using linear mixed effects modeling, with County as a random effect. We looked at variables for the year of (T) and year preceding (T-1) deer harvest. We found significant negative effects for area of planted winter wheat (T-1), corn (T), soybeans (T), and number of days with snow on the ground (T). We found a significant positive effect of areas with unharvested corn and soybeans (T-1). Given our candidate models, our results indicated that yearling deer antler sizes in southern Michigan showed a significant relationship to crop dynamics. The negative effects of planted winter wheat, corn, and soybeans are likely linked to corn and soybean farming practices that result in bigger and cleaner fields, less waste grain, and loss of winter cover. Unharvested corn and soybeans during the winters when the deer are fawns appear to offset these negative impacts.  Our results also suggest that winter severity while deer are fawns negatively affects yearling antler sizes. Our study has implications for state wildlife management agency technical assistance and outreach programs to private landowners, specifically regarding how crop residuals are managed. Deer managers may also account for the influence of these variables when relying on yearling antler beam diameters as an index to condition of deer populations.

Monday February 6, 2017 4:00pm - 4:20pm CST