A comparison of white-tailed deer recruitment rates to relative predator abundance in Maryland
Date
2017
Authors
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Publisher
University of Delaware
Abstract
In the late 1990s, Maryland’s deer management plan aimed to reduce and stabilize the state’s white-tailed deer (Odocoileus virginianus) population. While attempting to achieve this goal through liberalized seasons and bag limits, managers estimated a decreasing fawn recruitment rate and sought to better understand causes for these declines, particularly in the western portion of the state. Fawn recruitment may be impacted by several factors: predation, disease, starvation, malnutrition, parasite-load, and collisions with vehicles and farm machinery. My study’s goal was to better understand the predator-prey relationship within western Maryland. One hypothesis is the predator community reducing the fawn recruitment. In western Maryland, black bear (Ursus americanus), bobcat (Lynx rufus), and coyote (Canis latrans) are established, but the variation in abundance of these populations has not been well documented. I established 3 study areas focused on 3 publicly hunted state forests (Potomac-Garrett, Savage River, and Green Ridge State Forests). The first objective was to estimate the deer density and fawn recruitment at each study area. I used road-based distance sampling using a forward-looking infrared (FLIR) device to scan the landscape from August-October, 2015 and 2016. I replicated the FLIR survey 6 times on each study area in 2015 and 2016. Once collected, the data were analyzed using a uniform-key function within program DISTANCE. Neither deer density (Potomac-Garrett = 16 deer/km2, Savage River = 6 deer/km2, Green Ridge = 12 deer/km2) nor fawn recruitment (Potomac-Garrett = 0.56 fawn/doe, Savage River = 0.54 fawn/doe, Green Ridge = 0.52 fawn/doe) changed between years. ☐ My second objective was to estimate a relative predator (black bear, bobcat, and coyote) density among study areas. Each study area contained a systematic grid of 20 cameras spaced 3.2-km apart. This grid created an 8-km2 buffer around each camera to maintain site independence based on the average home range size of my target species. Cameras were deployed from June-August for a 60-day survey period in 2015 and 2016. Throughout the study, I logged 6,300 camera trap nights during the summer months. To compare predator densities using optimal sampling protocol, I performed an additional 60-day camera survey from December 2016-February 2017, logging 3,300 camera trap nights. I analyzed all data using Royal and Nichols (2004) N-Mixture Model within package unmarked for R 3.0.3 software. Predator densities shared 95% confidence intervals among sites and years. The average yearly mean and standard error of black bear density for each state forest were: Potomac-Garrett: M = 0.35, SE =0.10 bear/km2, Savage River: M = 0.51, SE = 0.12 bear/km2, and Green Ridge: M = 0.28, SE = 0.07 bear/km2. The average yearly mean and standard error of bobcat density for each state forest were: Potomac-Garrett: M = 0.10, SE =0.11 bobcat/km2, Savage River: M = 0.13, SE = 0.14 bobcat/km2, and Green Ridge: M = 0.09, SE = 0.11 bobcat/km2. The average yearly mean and standard error of coyote density for each state forest were: Potomac-Garett: M = 1.84, SE = 1.10 coyote/km2, Savage River: M = 0.88, SE = 0.55 coyote/km2, and Green Ridge: M = 0.19, SE = 0.16 coyote/km2. Finally, I compared fawn recruitment to the predator densities at each of the 3 study areas. The results of our study indicated a stable, albeit on the low side of fawn recruitment but variable predator density across the landscape, suggesting that the predator community is not lowering the fawn recruitment.