Human-Imprinted Northern Bobwhite Chicks and Indexing Arthropod Foods in Habitat Patches

Abstract

Arthropods are an important diet resource for northern bobwhite (Colinus virginianus) chicks. Estimates of arthropod abundance using standard entomological sampling techniques may lack biological relevance for assessing potential foraging value of habitat patches because they do not incorporate a realistic availability measure of arthropods to bobwhite chicks. Assuming that human-imprinted (hereafter, imprinted) bobwhite chicks foraged similarly to wild bobwhite chicks, we estimated foraging rates (arthropods [g] consumed/30 min/chick) and mass (g) changes of imprinted chicks foraging in different habitat patches, and used these measures to index arthropod abundance. Ranks of arthropod abundance in soybean fields (n = 8) based on foraging rates of imprinted chicks were different from ranks based on arthropod counts from sweepnet sampling. Ranks of arthropod abundance in soybean fields (n = 10) based on mass changes of imprinted chicks were different from ranks based on dry mass (g) of arthropods collected by sweepnetting and pitfall trapping. However, ranks of habitat patches based on foraging rates and mass changes of imprinted chicks were similar. Estimated sample sizes for comparing chick foraging rates of 2 agricultural habitats, with power (1-β) = 0.8 and α = 0.05, were reasonable (n ≤ 11) at observed levels of sampling error. Foraging rates of imprinted chicks in randomly selected, conventionally tilled soybean and corn fields were low (range 0.09-0.12 g/30 min/chick), but foraging rates were 2.1 and 3.8 times greater along field edges and in no-tilled fields, respectively. Our results suggest that using estimates of arthropod abundance to rank the foraging value of habitats may be unreliable without information on availability of arthropods to chicks. Indices of the foraging value of habitat patches based on imprinted bobwhite chicks were more biologically relevant than arthropod abundance information.