Spring Dispersal and Breeding Ecology of Northern Bobwhite in Southwest Ohio
Marjorie R. Liberati, MS
Advisor: Robert J. Gates
Northern bobwhites are a popular upland game bird species with economic and social importance. Despite nearly a century of research, population declines continue at state and national scales. Precipitous population declines and range-contractions in the Midwest have been caused by land-use changes and suppression of natural disturbance regimes. Reproduction that meets or exceeds annual mortality is essential to sustain viable populations and poor reproductive success is also implicated in declines of grassland bird populations. This study fills an information gap in knowledge of spring dispersal, breeding ecology and behavior, and breeding vital rates of Midwestern bobwhites near the northern limit of their range. It is unclear if recovery of Midwestern bobwhite populations is limited by spring dispersal capabilities and/or breeding vital rates.
Radio-telemetry was used to investigate breeding vital rates during 2010 and 2011 on 4 private-lands study sites in southwest Ohio. Bobwhites were outfitted with radio-transmitters with an 8-hr mortality sensor and tracked daily with homing to within ≤ 20 m. Spring dispersal and breeding season vital rates were evaluated and compared to other bobwhite populations to identify potential population-limiting factors associated with spring dispersal and reproduction. Vital rates that met or exceeded range-wide means included spring dispersal distance (1.54 km), nesting effort (re-nest = 26%, double clutch = 65%), male incubation (43% of nests), clutch size (14.4 eggs), egg success (96.9%), and nesting phenology. The mean hatch date for first nest attempts was 1 July, 21 July for male incubated nests, 28 July for renests, 31 July for backdated fall-juveniles, and 24 Aug for double clutches. Breeding season (Apr-Sep) survival (28%) and nest success (27.9%) were lower in southwestern Ohio compared to range-wide averages.
Relatively low nest success and breeding season survival indicates that reproduction may limit population growth in this region and that availability of quality breeding habitat is below the threshold needed to offset annual mortality. Providing early successional woody cover within landscapes could improve annual survival and reverse bobwhite population declines in the Midwest. Early successional woody habitat was highly selected at multiple spatial scales during the breeding season. Bobwhites with higher proportions of early succession woody habitat in their nonbreeding home ranges were less likely to disperse or dispersed shorter distance in spring (P = 0.006). Although woody cover was an important component of spring-summer habitat for bobwhites, nest success declined with increasing amounts of woody cover near nest sites (P = 0.05).
Continuing support for programs like the Conservation Reserve Program (CRP) that establish permanent, managed grasslands remain important for bobwhite conservation in the Midwest. Vegetation succession coupled with anticipated declines in CRP enrollment would likely diminish usable space for bobwhites in the Midwest during the breeding season and negatively impact nest success. Bobwhites in the agricultural Midwest would benefit from having woody cover in proximity to grassland habitats during the breeding season but woody encroachment within grassland habitats where bobwhites nest should be managed.