Urban birds’ tolerance towards humans was largely unaffected by increased variation in human levels due to COVID-19 shutdowns

Abstract

The coronavirus disease 2019 (COVID-19) pandemic has dramatically altered human activities, potentially relieving human pressures on urban-dwelling animals. Here, we evaluated whether birds from five cities in five countries (Czech Republic - Prague, Finland - Rovaniemi, Hungary - Budapest, Poland - Poznan, and Australia - Melbourne) changed their tolerance towards human presence (measured as flight initiation distance) during the COVID-19 shutdowns. We collected 6369 flight initiation distance estimates for 147 bird species and found that birds tolerated approaching humans to a similar level before and during the COVID-19 shutdowns. Moreover, during the shutdowns, bird escape behaviour did not consistently change with the level of governmental restrictions (measured as the stringency index). Hence, our results indicate that birds do not flexibly and quickly adjust their escape behaviour to the reduced human presence; in other words, the breeding populations of urban birds examined might already be tolerant of human activity and perceive humans as relatively harmless.

Lockdown effects on fear revealed direct and indirect effects of human presence on perceived predation risk

“…Singing birds posted higher than non-singing birds, and post height was not affected by either habitat or the lockdown, suggesting strong stabilizing selection for song post height selection and/or low behavioral flexibility for this trait (Møller, 2011). Our results disagreed with those of a recent similar study based on much lower sample sizes measured in four European and one Australian cities (Mikula et al, 2022), where no significant changes in FIDs during lockdown were found. Low power to analyze a heterogeneous data set may account for this contrasting result, as responses of urban birds to lockdown have proven to be generally clear-cut (Derryberry et al, 2020;Montgomery et al, 2021).…”

“…Differential responses to lockdown are thus expected according to habitat, height above ground and singing behavior if indirect effects of humans mediate effects of human presence on FIDs. These differences are not expected in a scenario of direct effects of human disturbance, that would lead to either increased, decreased or invariant FIDs across habitats, bird locations and singing behaviors (Díaz et al, 2013;Samia et al, 2015;Mikula et al, 2022). Specifically, we expected a) differential lockdown effects in urban as compared to nearby rural habitats, with stronger changes in the latter due to lower sensitivity of urban bird populations to changes in environmental conditions (Díaz et al, 2021); b) lack of changes in height above ground of birds when flushed if lockdown decreased direct human disturbance effects, and increased height in the urban an decreased height in rural habitats if effects were mediated by predator release (ground-dwelling predators are prevalent in urban habitats whereas aerial predators prevail in rural habitats; Møller, 2011;Díaz et al, 2022); c) stronger responses to lockdown by non-singing (i.e., foraging or resting) birds than by singing birds, due to constraints imposed by selection of optimal singing heights (Møller, 2011); d) differential adjustments of vertical and horizontal components of FID if predator release is at stake, by increasing the latter according to the former (i.e.…”

“…We were thus able to sample during (2020) and after (2021) the Covid-19 lockdown the same areas we sampled before lockdown (2018) in previous studies (Díaz et al, 2013(Díaz et al, , 2021(Díaz et al, , 2022. Paired comparisons according to study sites (see below) control for among-sites (cities and surrounding rural areas) variation in other factors potentially influencing FIDs, such as vegetation structure, human population density or the level of governmental restrictions (Díaz et al, 2022;Mikula et al, 2022;Morelli et al, 2022).…”

Urban birds become less fearful following COVID-19 reopenings

“…It could be that urban colonists from non-urban origins might have a lower baseline fear response in comparison to the non-urban population at large, and potentially decrease their fear response with human activity. We note, that in contrast to virtually all other studies of anthropause effects in birds (e.g., 1,3,4,28–30 ) that used unmarked birds and were unable to focus on individuals, these insights emerged only from a detailed, longitudinal study of individuals.…”

“…Collectively, our results suggest that changes in fear responses might not be as predictable as we might expect, and likely depends on which individuals and how their behaviors develop and shift in combination with strong and rapidly shifting collective human behaviors. Only through studies on individual animals tracked over time can we understand the mechanisms underlying population response, which cannot be confirmed from contradictory broadscale patterns found in metanalyses 28,30 . While the anthropause created much human hardship, it offered a unique opportunity to identify an important new avenue of ontogenetic research that can create insights which will help us better conserve biodiversity in a rapidly changing, human-dominated world.…”