A Monte Carlo model for estimating the productivity of a generalist brood parasite across multiple host species

Questions: How can the productivity of a generalist brood parasite be estimated? Does an invasive brood parasite have greater productivity (defined as fledglings/egg and fledglings/area) in a recently invaded habitat than in a habitat similar to its original range? Features of model: We developed a simulation model that uses Bayesian and Monte Carlo methods to integrate brood parasite productivity across multiple host species over the entire breeding season. Organisms: We use the model to estimate the productivity of the brown-headed cowbird (Molothrus ater) in two host communities, one breeding in deciduous forests (a recently invaded habitat) and one in old fields (a grassland habitat more similar to the cowbird's original range). We parameterize the model with data from 616 nests of 14 cowbird host species, containing 428 cowbird eggs and young. Results and conclusions: We developed methods for estimating the productivity of a brood parasite with an entire community of host species. We found that cowbirds have higher productivity in the recently invaded habitat, deciduous forest. Our findings are consistent with the rapid spread of the cowbird once it invaded the forested eastern United States.