Recent Increase in the Yellow-billed Magpie Population in Sacramento and Its Possible Causes

Abstract

The Yellow-billed Magpie (Pica nuttalli) declined substantially throughout its range after the West Nile virus arrived in California in the 2000s, and neither development of disease resistance nor population recovery have been reported. After surveying 8 occupied sites in 2020 and 22 occupied sites in 2021 for a study of the magpie’s habitat use in urban Sacramento, I continued surveying 15 urban parks in 2022 and 2023 to evaluate population trends over 4 years. The Sacramento magpie population increased consistently by 3–7% per year, suggesting a localized recovery. Since the extent of foraging habitat remained stable, other factors, possibly including development of resistance to the virus (as seen in other species of birds), may be promoting a population increase. These results, however, are local and relatively short term. More work is needed to determine if resistance is developing and to understand longer-term population and disease trends in other parts of the Yellow-billed Magpie’s range.