TWEL Adam Janke Thesis

Survival and habitat use of non-breeding northern bobwhites on private lands in Ohio
 
Adam K. Janke, MS 
Advisor: Robert J. Gates
 
 
Despite a long history of research and accumulated knowledge of factors affecting population growth rates, conservation efforts aimed at reversing population declines of northern bobwhites (Colinus virginianus) have been largely ineffective. Bobwhite population decline and range contraction across the Midwest was driven primarily by changes in land-use practices related to large-scale intensive agriculture, urbanization, and forest succession. Although changes in agricultural landscapes have contributed substantially to the decline, such landscapes remain the only area where active management may improve population growth rates. To understand the ecology of bobwhites in agricultural landscapes in Ohio, I used radio-telemetry to investigate survival and habitat use during the non-breeding season (October - March) on 4 private land study sites in southwestern Ohio during 2009-2011. Known-fates survival estimates were low in both years (Ŝ 2009-2010=0.05, 95% CI=0.03, 0.11, Ŝ 2010-2011=0.12, 95% CI=0.07, 0.20) and lowest weekly survival coincided with periods of prolonged snow cover. Compositional analysis revealed that coveys used habitat non-randomly at 3 scales; positioning of home ranges within study areas (Λ = 0.320, P < 0.001), positioning of core areas within home range (Λ = 0.599, P = 0.002), and point locations within home ranges (Λ = 0.058, P = 0.002). Early successional woody vegetation (e.g. fencerows and ditches) was the most preferred habitat type at all scales. Differences in selection among study sites revealed that home ranges were preferentially established in areas with grassland cover on 2 agricultural study sites, but not at the site with the greatest amount of grassland cover. Bobwhites mostly used habitat edges such that interior portions of grass and crop fields were used less as they increased in area. Thus small fields with high edge to interior ratios are most advantageous.
 
I tested the influence of habitat use on individual survival by comparing models representing habitat use at 4 spatial scales; site, landscape (78.5 ha buffer), home range, and microhabitat use. Support for different models at 2 scales showed scale-dependent effects of habitat on survival. Higher woody edge density within home ranges was associated with higher survival whereas increasing perennial cover within a 78.5 ha buffer around individuals was related to diminished survival. This relationship suggested that survival was influenced by habitat availability at smaller scales and by factors that affect predator distribution at larger scales. Given the important influence of low non-breeding season survival on population growth rates, management strategies should focus on improving non-breeding season survival in this population by providing woody cover near food sources (e.g. grasslands and row crop fields). Intermediate amounts of grassland and row crop habitat are important in agricultural landscapes, but overrepresentation of any 1 cover type will diminish the suitability of the site for bobwhites during the non-breeding season. Practices focused on improving woody edge habitat along forests are likely to only marginally affect crop production but could significantly improve the amount of usable habitat for bobwhites in agricultural landscapes.