EFFECTS OF AGRICULTURAL LAND CONVERSION AND LANDSCAPE CONNECTIVITY ON MOVEMENT, SURVIVAL, AND ABUNDANCE OF NORTHERN BOBWHITES (COLINUS VIRGINIANUS) IN OHIO
Olivia M. Smith, MS
Advisors: Brian K. Slater and Eric Toman
Conversion of land for agriculture and agricultural intensification are widely recognized as two of the largest threats to biodiversity. The northern bobwhite (Colinus viginianus) is one of the fastest declining species in North America primarily due to farmland conversion and agricultural intensification. Bobwhites declined 4.08% annually from 1966-2013. Bobwhites in Ohio declined 6.88% per year during the same period. As a part of a larger study that aimed to assess bobwhite demographics, this study aimed to better understand how land use conversion and farmland management affect bobwhite fall dispersal, survival, and summer abundance.
Radio telemetry was used to monitor bobwhites year round in the breeding (1 Apr-30 Sep 2010 and 1 Apr-30 Sep 2012-2014) and nonbreeding (1 Oct-31 Mar 2009- 2011 and 1 Oct-31 Mar 2012-2015) seasons on 4 study sites located on private lands in Ohio. Home ranges were constructed for each individual in each season (n = 26). Cover maps were clipped and overlaid with summer home range boundaries to quantify home range composition. The average shift from the center of the summer home range to the center of the winter home range was 515 ± 139 (SE) m. Average overlap between seasonal home ranges was 34% or 5.0 ± 1.1 (SE) ha. The model with the most support (wi = 0.45) of distances moved between summer and fall winter home ranges included summer home range percent early-successional (ES) woody cover (β = -3.44 ± 1.75 (SE)), summer home range forest edge density (β = -0.017 ± 0.005 (SE)), mean nearest neighbor of ES woody (β = 0.0007 ± 0.0002 (SE)), and summer interspersion juxtaposition index of ES herbaceous habitat (β = 0.005 ± 0.002 (SE)) with a random location effect. Though there was not a significant correlation between overwinter survival and the degree of home range shift, bobwhites shifted home ranges more in fall when summer habitat was of poorer quality for winter survival. However, this shift was on average about a half kilometer suggesting a limited dispersal ability. Bobwhites in Ohio likely need winter cover close to nesting and brood rearing habitat.
Whistle count surveys were conducted from 2008-2010 and 2012-2014 on 29 survey points across ≥ 5 of the 6 years. Landscape composition was classified around each survey location by using a 1-km buffer on aerial photographs. In 2012, ES woody vegetation was created by treating edges in 12 survey points on 2 study sites. A total of 1096 male bobwhites were detected. The detection probability for 2008-2009 and 2012- 2014 was 0.503 ± 0.0274 (SE). The detection probability for 2010 was estimated to be 0.400 ± 0.0389 (SE) which was analyzed separately due to differences in recording. The pooled estimate between sites was a decline of -0.512 detections per point per year. ES woody was the only habitat type to show a significant result in response to habitat change (χ12 = 4.94, P = 0.026) and was positively correlated with change in abundance (1.08 ± 0.48 (SE) detections per survey point per year). These results suggest addition of treated edges may help slow population decline at a small scale.
Project sponsor: Ohio Division of Wildlife