Urban birds become less fearful following COVID-19 reopenings

Abstract

Following the COVID-19 pandemic, many people around the world stayed home, drastically altering human activity in cities. This exceptional moment provided researchers the opportunity to test how urban animals respond to human disturbance, in some cases testing fundamental questions on the mechanistic impact of urban behaviors on animal behavior. However, at the end of this 'anthropause', human activity returned to cities. How might each of these strong shifts affect wildlife in the short and long term? We focused on fear response, a trait essential to tolerating urban life. We measured flight initiation distance at both individual and population-levels for an urban bird before, during, and after the anthropause to examine if birds experienced longer-term changes after a year of lowered human presence. Dark-eyed juncos did not change fear levels during the anthropause, but they became drastically less fearful afterwards. These surprising and counter-intuitive findings, made possible by following the behavior of individuals over time, has led to a novel understanding that fear response can be driven by plasticity, yet not habituation-like processes. The pandemic-caused changes in human activity have shown that there is great complexity in how humans modify a behavioral trait fundamental to urban tolerance in animals.

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

“…with the time since urbanization [49,50]. However, a recent study using individually marked dark-eyed juncos (Junco hyemalis) showed, similar to our findings, weak effects of the COVID-19 shutdowns on flight initiation distance in urban birds [22]. The weak response of birds to long-term changes in human levels may indicate that (i) birds react to long-term shifts in human behavior in a nonlinear manner (which has to our knowledge never been tested) and/or such (ii) shifts in human behavior have to reach a threshold value to trigger observable changes in bird behavior.…”

“…To test whether the response of birds to changing human levels is non-linear or based on threshold human levels, repeated escape distance trials of marked individuals during various times of day and different days of the week, as well as under various natural or experimentally induced levels of human presence and activity are needed. However, most studies that investigated escape responses of animals towards humans and used marked individuals did not expose these individuals to the various levels of human disturbance ( [48,[51][52][53], but see [22]).…”

“…Consequently, the COVID-19 shutdowns might have elicited complex effects on urban nature [10]. For example, some animals increased their abundances in humandominated landscapes, moved to new areas, or shifted the timing and character of their activities; some of these effects were area-or species-specific [10,11,[16][17][18][19][20][21][22][23] To persist in urban habitats, wild animals must increase their tolerance to humans and human disturbance [24,25]. Indeed, on a gradient from natural to urban environments animals seem more tolerant of humans, where human densities are high and human-wildlife interactions are generally harmless [24,[26][27][28][29].…”

“…Additionally, within cities animal tolerance to humans seems to increase with increasing level of human presence (hereafter "human presence") but the association is often weak [30][31][32][33]. Whether the COVID-19 shutdowns induced changes in human activities and subsequently altered the urban landscape of fear and animal responses to human presence is still poorly understood [22,34].…”

Urban birds become less fearful following COVID-19 reopenings

“…Data and code are accessible via Figshare: https://doi. org/10.6084/m9.figshare.21743810 [62]. Supplementary material is available online at [63].…”