Estimating white-tailed deer abundance at Gettysburg National Military Park and Eisenhower National Historic Site

Stainbrook, David; Diefenbach, Duane

To increase regeneration in woodlots and reduce crop damage, the National Park Service (NPS) began culling deer in 1995 to reach a density goal of 10 deer/km2 of forest. However, park managers were interested in an accurate population estimate to determine if their management goal has been met and possible methods to monitor future abundance. Deer density estimates, among all surveys and survey methods, ranged from 43−71 deer/km2 of forest. Our estimates indicated density is approximately four times greater than the park’s goal of 10 deer/km2 of forested land specified in the GNMP-ENHS deer management plan. However, NPS staff have observed increased tree regeneration and reduced crop damage on NPS-owned property since culling was initiated. Additionally, we observed more deer on private lands in the study area and fewer deer on NPS-owned property. We investigated the feasibility and assumptions of multiple abundance estimators. We examined whether harvest data from culling operations could be used to estimate abundance within the GNMP-ENHS study area, which included lands adjacent to GNMP-ENHS, using a catch-per-unit-effort (CPUE) estimator. We investigated a change-in-ratio (CIR) estimator based on data collected during culling operations. Also, we captured and fitted adult and juvenile male and female deer with Global Positioning System (GPS) collars and performed surveys at dusk and at night from April 2009–November 2010 to estimate abundance using mark-resight methods. Also, we used these data to estimate an updated detection probability that could be used to adjust counts obtained during future dusk surveys. Additionally, we conducted distance sampling surveys from roads at night to obtain population estimates and to test assumptions when roads are used as transects with distance sampling.

Estimating white-tailed deer abundance at Gettysburg National Military Park and Eisenhower National Historic Site

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