Nest parasitism by Brown-headed Cowbirds (Molothrus ater) can negatively affect host populations. Landscape-scale factors, such as proximity to residential areas, equestrian riding stables, and grazing allotments, can affect the risk of nest parasitism as well as the abundance of Brown-headed Cowbirds, Recent increases in residential and recreational development along with a reduction in grazing allotments in the northern Sierra Nevada provide an opportunity to reevaluate factors that influence frequency of nest parasitism by Brown-headed Cowbirds, Frequency of nest parasitism increased as the distance to the nearest residential center and distance to the nearest equestrian riding stable decreased. Similarly, Brown-headed Cowbird abundance was negatively correlated with distance to the nearest residential center and distance to the nearest equestrian stable. To reduce the risk of nest parasitism, efforts should be devoted to (1) reducing further residential development at the wildland—urban interface and (2) educating landowners about bird feeders, which frequently attract Brown-headed Cowbirds.