Breeding in the pandemic: Short-term lockdown restrictions in a European capital city did not alter the life-history traits of two urban adapters

Humans are transforming natural habitats into managed urban green areas and impervious surfaces at an unprecedented pace. Yet the effects of human presence per se on animal life-history traits are rarely tested. This is particularly true in cities, where human presence is often indissociable from urbanisation itself. The onset of the SARS-CoV-2 outbreak, along with the resulting lockdown restrictions, offered a unique, "natural experiment" context to investigate wildlife responses to a sudden reduction of human activities. We analysed four years of avian breeding data collected in a European capital city to test whether lockdown measures altered nestbox occupancy and life-history traits in terms of egg-laying date, incubation duration, and clutch size in two urban adapters: great tits (Parus major) and blue tits (Cyanistes caeruleus). Lockdown measures, which modulated human presence, did not influence any of the life-history traits investigated. In contrast, tree cover, a distinct ecological attribute of the urban space, was positively associated with clutch size, a key avian life-history, and reproductive trait. This highlights the importance of habitat quality/ inter-year variation over human activity on the reproduction of urban wildlife. We discuss our results in light of other urban wildlife studies carried out during the pandemic, inviting the scientific community to carefully interpret all lockdown-associated shifts in biological traits.