Can low-precision population and survival estimates of deer be accurate?

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Wildlife Society Bulletin


To obtain baseline density data for population modeling and zone-specific management of deer (Odocoileus spp.), we monitored 34 radiocollared white-tailed deer (O. virginianus) in and around Myles Standish State Forest, southeastern Massachusetts, during winters 1997-2000. Our objectives were to 1) identify factors influencing the precision of aerial population estimates; 2) estimate cause-specific mortality rates of adults; 3) use population estimates, mortality rates, and other reasonable assumptions to calculate an average harvest; and 4) compare this estimate with state-reported harvest to assess the accuracy of our density and survival data. Two to 5 mark-resight helicopter surveys completed in each of 3 successive winters resulted in density estimates ranging from 4.7-6.5 deer/km2 (x̄=5.7 deer/km2). The low proportion of marked individuals in our survey areas (annual x̄=8-10%) was due to poor capture success, while low observability (annual x̄=7-15%) was due to lack of snow cover and the preponderance of pine (Pinus spp.) cover. These conditions resulted in low-precision estimates (x̄ 90% Cl=59-222% of point estimate). Annual survival of 22 adult female deer (>1.0 yr old) was 0.87 (95% Cl = 0.79-0.96) versus 0.81 (95% Cl=0.68-0.96) for 12 adult males. Sources of female mortality included hunting (annual rate=0.05), poaching (0.03), and unknown causes (0.06); males were hunted (0.16) and died from unknown causes (0.03). Adult deer density and cause-specific mortality data, combined with assumed estimates of age ratios (30% fawns) and adult sex ratios (60% F) in winter, predicted annual legal harvest of 0.14 adult females and 0.30 adult males/km2, which approximated the recorded harvest for the surrounding management area (0.17 and 0.30, respectively). Despite low precision, mean point estimates of deer density and survival could be accurate.







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