The impact of forest fragmentation on rates of nest parasitism was estimated by the percentage of developed land within 20 kilometers (km) of the nest, which corresponds to the maximum foraging distance for cowbirds In order to assess the relationship between forest fragmentation and the impact of nest parasitism on forest birds, Penn Lloyd and colleagues (2005) used data from the Breeding Biology and Monitoring Database to assess the frequency of nest parasitism and annual fecundity of 15 species of forest-dwelling birds in the United States (Figure 1). The impact of forest fragmentation on rates of nest parasitism was estimated by the percentage of developed land within 20 kilometers (km) of the nest, which corresponds to the maximum foraging distance for cowbirds