Are domestic cattle bringing brown-headed cowbirds to new habitats?
The brown-headed cowbird (Molothrus ater) (hereafter cowbird) is an obligate brood parasite (it lays its eggs in other birds’ nests) that has the potential to significantly reduce the nest success of host birds. Historically, cowbirds associated with bison (Bison bison) as the presence of bison likely increased foraging opportunities by creating microhabitats for insects, increasing insect abundance, as well as flushing insects in their wake. Today, cowbirds are known to associate with domestic cattle, likely for the same reasons, and may be exposing naïve bird species to nest parasitism in areas where bison were not historically present in large numbers. This study examines the association of cowbirds with cattle by using bioacoustic and camera trap data on a regional scale to determine if the presence of cattle is correlated with higher than expected occurrence of cowbirds. The interaction between cattle and cowbirds is estimated using an occupancy and generalized linear modeling approach relative to the estimated habitat suitability derived by the Alberta Biodiversity Monitoring Institute (ABMI) and the presence or absence of cattle. Results indicate the the probability of occupancy for cowbirds is higher than expected in areas with low habitat suitability for cowbirds where cattle are present.