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.