Effect of field borders and nest-predator reduction on abundance of northern bobwhites

Abstract

Fallow-field borders along edges of crop fields have been promoted for increasing northern bobwhites (Colinus virginianus) on farms and are a component of recovery plans for this species. However, research on bobwhite population response to field-border practices is sparse. Previous research on 2 farms documented increased use of farm fields and greater reproduction by bobwhites on farms with field borders, but nesting success was low during May and June. Bobwhite population response to field-border practices may increase when they are combined with nest-predator reduction on farms. Effect of nest-predator reduction on bobwhite populations on farmed landscapes has not been investigated in the Southeast. Therefore, we tested the effects of field borders and mesomam-mal nest-predator reduction on bobwhite abundance on 12 farms in eastern North Carolina, 1997–1999. We applied treatments to farms as factorial combinations. Reduction of mesomammal nest predators, including raccoons (Procyon lotor), Virginia opossums (Didelphis virginiana), and foxes (Urocyon cinereoargenteus and Vulpes vulpes), occurred from February-May of each year. To assess bobwhite response to treatments, we measured summer abundance of males using variable-radius point counts and covey abundance on farms in September and October using morning covey-call surveys. Bobwhites were more abundant on farms with field borders during summer (P=0.08). On field-border farms we heard 1.8x the number of coveys heard on farms without field borders (P=0.004). Summer abundance of bobwhites did not differ as a result of predator reductions (P=0.37), and we heard slightly fewer coveys on predator-reduction farms (P = 0.084) during autumn. However, we heard more coveys on farms with both field borders and predator reduction compared to all other farms (P=0.022). Field-border systems were a practical management technique to increase autumn abundance of bobwhites on individual farms in eastern North Carolina.