Contrasting effects of the COVID-19 lockdown on urban birds’ reproductive success in two cities

Abstract

The ubiquitous activity of humans is a fundamental feature of urban environments affecting local wildlife in several ways. Testing the influence of human disturbance would ideally need experimental approach, however, in cities, this is challenging at relevant spatial and temporal scales. Thus, to better understand the ecological effects of human activity, we exploited the opportunity that the city-wide lockdowns due to the COVID-19 pandemic provided during the spring of 2020. We assessed changes in reproductive success of great tits (Parus major) at two urban habitats affected strikingly differently by the ‘anthropause’, and at an unaffected forest site. Our results do not support that urban great tits benefited from reduced human mobility during the lockdown. First, at one of our urban sites, the strongly (− 44%) reduced human disturbance in 2020 (compared to a long-term reference period) did not increase birds’ reproductive output relative to the forest habitat where human disturbance was low in all years. Second, in the other urban habitat, recreational human activity considerably increased (+ 40%) during the lockdown and this was associated with strongly reduced nestling body size compared to the pre-COVID reference year. Analyses of other environmental factors (meteorological conditions, lockdown-induced changes in air pollution) suggest that these are not likely to explain our results. Our study supports that intensified human disturbance can have adverse fitness consequences in urban populations. It also highlights that a few months of ‘anthropause’ is not enough to counterweight the detrimental impacts of urbanization on local wildlife populations.

Extreme Hot Weather Has Stronger Impacts on Avian Reproduction in Forests Than in Cities

“…Finally, life-history changes may also help animals to cope with the direct effects of urban heat. For example, urban birds usually have smaller clutch size than forest birds (Chamberlain et al, 2009), which is also typical in our study populations (Seress et al, 2018(Seress et al, , 2021. Smaller clutch size may also be advantageous for heat dissipation when environmental temperature is high because fewer offspring produce less heat and have more space to maintain distance in the nest, which helps better heat conduction.…”

Avian behaviour changes in response to human activity during the COVID-19 lockdown in the United Kingdom

“…For example, increases or decreases in the use of certain habitats by birds do not necessarily translate to benefits/costs to their populations or reproductive success (e.g. [38,39]. Nonetheless, it is clear that the impacts of pandemic lockdowns on birds varied significantly and in highly ecologically important ways.…”

“…As bird abundance can be affected by human presence and activity [38], we evaluated whether changes in different types of human mobility patterns as a result of COVID-19 restrictions affected counts of 25 avian species across a wide range of habitat types. Exploring whether the number of birds seen during the first pandemic lockdown differed from those recorded prior to lockdowns, and evaluating whether bird counts changed more on days and in regions with greater changes relative to various indices of human mobility (time spent at home, parks and grocery) allowed us to examine the relationships between habitat type (e.g.…”

Phenotypic plasticity and the anthropause: an urban bird becomes less aggressive

“…Nestling great tits in busier parks had worse body condition, indicating that adults invested less energy in parental provisioning compared to the prior year when human disturbance was not as intense. However, the body condition of chicks in less-attended parks did not improve versus a typical year, suggesting that short-term relief from human disturbance is not enough to confer lasting benefits to urban birds (8).…”

“…Urban landscapes often have high concentrations of paved surfaces and artificial structures (1), light, noise, and chemical pollution (2), and abundant exotic wildlife and vegetation, including unfamiliar predators (3). Crucially, urban wildlife must be able to tolerate high frequencies of human disturbance (4)(5)(6)(7)(8). Any of these factors can disrupt a species' ability to acquire resources, communicate, or reproduce, thus limiting which species can successfully establish populations in cities (9)(10)(11)(12)(13)(14).…”