Lockdown effects on fear: direct and indirect effects mediated by release of urban predators

The Covid-19 lockdown reduced drastically human presence outdoors, providing an uncontrolled experiment for disentangling direct and indirect effects of human presence on animal fearfulness. We measured 18,494 flight initiation distances (FIDs, the distance at which individual animals fly away when approached by a human) from 1,333 populations of 202 bird species taken in four European cities both before, during and after the lockdown. Differential responses to lockdown among urban and rural habitats and between signing and non-singing birds showed that lockdown relaxed direct disturbance effects on birds in rural habitats, but increased indirect fear effects mediated by predator release (mainly feral cats) in cities.