Phenotypic plasticity in the anthropause: does reduced human activity impact novel nesting behaviour in an urban bird?

The COVID-19 pandemic temporarily transformed urban ecosystems by restricting public human activity to only the most essential societal functions, even as other landscape level factors such as the built environment remained unchanged. In so doing, it provided a unique opportunity to experimentally answer questions about the role of human disturbance in driving behavioural adaptation in urban wildlife. We compared nesting data collected on an urban dark-eyed junco, Junco hyemalis, population nesting on the University of California, Los Angeles (UCLA), U.S.A. campus during the 2021 nesting season, when the campus restrictions were in effect, to a similar data set collected in 2019, before the pandemic, in order to examine (1) whether urban dark-eyed juncos on the UCLA campus altered their use of novel off-ground and artificial nesting sites in response to reduced human activity and (2) whether reduced human activity impacted nesting success. We found that after a >80% reduction in human activity, junco nesting success during the COVID-19 pandemic modestly increased compared to prepandemic levels. However, nest site selection remained unchanged. Our findings suggest that the landscape of the built environment or urban predators, rather than disturbance by human activity, drives novel nest site selection in urban birds.