Breeding Season Survival of American Woodcock at a Habitat Demonstration Area in Minnesota
Kyle O. Daly
Minnesota Cooperative Fish and Wildlife Research Unit, Department of Fisheries, Wildlife, and Conservation Biology
David E. Andersen
U.S. Geological Survey, Minnesota Cooperative Fish and Wildlife Research Unit
Wayne L. Brininger
U.S. Fish and Wildlife Service, Tamarac National Wildlife Refuge
Thomas R. Cooper
U.S. Fish and Wildlife Service, Migratory Bird Program
DOI: https://doi.org/10.24926/AWS.0108
Abstract
American woodcock (Scolopax minor; hereafter woodcock) best management practices (BMPs) applied at a landscape scale have been proposed to increase woodcock population densities, yet little information exists regarding population vital rates following application of BMPs. We estimated survival rates of woodcock adult females, nests, and juveniles at a woodcock habitat-management demonstration area in west-central Minnesota during the spring and summer (23 March – 30 June) of 2011 and 2012. We radio-marked and tracked 41 adult female and 73 juvenile woodcock, and monitored 51 broods and 48 woodcock nests to determine fates. We used Kaplan-Meier survival analysis to estimate survival rates of females, nests, and juveniles for both 2011 and 2012 and logistic-exposure models to assess relationships between survival and weather covariates, individual life history traits, and vegetation characteristics resulting from BMPs. Breeding season cumulative survival rate for adult females from 1 April – 30 June was 0.695 (95% CI: 0.357 – 1.052) in 2011, 0.740 (95% CI: 0.391 – 1.091) in 2012, and 0.751 (95% CI: 0.499 – 1.000) when pooling data from both years. Nest survival rate for the 24-day laying and incubation period was 0.458 (95% CI: 0.299 – 0.696) in 2011 and 0.786 (95% CI: 0.616 – 0.998) in 2012. Cumulative survival rate for juvenile woodcock for a 61-day period (1 May – 30 June) following hatch through mid-summer, when juveniles are independent from adults, was 0.330 (95% CI: 0.188 – 0.613) in 2011 and 0.576 (95% CI: 0.398 – 0.833) in 2012. In all logistic-exposure survival models, we included a year covariate (females: β2011= −0.16, 95% CI: −1.67 to 1.45, nests: β2011= −0.768, 95% CI: −1.70 to 0.166, juveniles: β2011= −0.85, 95% CI: −1.77 to 0.07) to account for between-year variation in survival rates, although removing that covariate in models did not result in changes in relations between survival rates and other covariates. Our best-supported model of female survival rate was the null model, suggesting female survival rate was constant across years, and our best-supported model of nest survival rate included only a year covariate. Our best-supported model of juvenile survival rate included the covariates year, juvenile age (βAGE = 0.098, 95% CI: 0.04 to 0.16), minimum temperature (βMINT = 0.14, 95% CI: −0.004 to 0.28), and precipitation (βPCPT = −0.20, 95% CI: −0.39 to −0.01). Juvenile survival rate increased with age and decreased with the amount of precipitation and had a weak positive relation with stem density (βSTEM = 0.0001, 95% CI: 0.000 to 0.0003). Woodcock in our study almost solely used areas where BMPs had been applied on the landscape within the last 20 years and that had similar vegetation structure; in those settings, only juvenile survival rate was related to local environmental conditions.
