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

Abstract

Climate change and urbanisation are among the most salient human-induced changes affecting Earth’s biota. Extreme weather events can have high biological impacts and are becoming more frequent recently. In cities, the urban heat island can amplify the intensity and frequency of hot weather events. However, the joint effects of heat events and urban microclimate on wildlife are unclear, as urban populations may either suffer more from increased heat stress or may adapt to tolerate warmer temperatures. Here, we test whether the effects of hot weather on reproductive success of great tits (Parus major) are exacerbated or dampened in urban environments compared to forest habitats. By studying 760 broods from two urban and two forest populations over 6 years, we show that 14–16 days-old nestlings have smaller body mass and tarsus length, and suffer increased mortality when they experience a higher number of hot days during the nestling period. The negative effects of hot weather on body mass and survival are significantly stronger in forests than in urban areas, where these effects are dampened or even reversed. These results suggest that urban nestlings are less vulnerable to extreme hot weather conditions than their non-urban conspecifics. This difference might be the result of adaptations that facilitate heat dissipation, including smaller body size, altered plumage and reduced brood size. Alternatively or additionally, parental provisioning and food availability may be less affected by heat in urban areas. Our findings suggest that adaptation to heat stress may help birds cope with the joint challenges of climate change and urbanisation.

Avian responses to climate extremes: insights into abundance curves and species sensitivity using the UK Breeding Bird Survey

“…For example, abundance of some corvids (Corvidae) such as the Eurasian magpie ( Pica pica ), the carrion crow ( Corvus corone ) and the Eurasian jay ( Garrulus glandarius ), as well as the common starling ( Sturnus vulgaris ) and the great tit ( Parus major ), positively responded to SU25. These species are often present in urban environments, and the effects of hot temperatures could be influenced by habitat characteristics with dampened or reverse effects in urban areas (Pipoly et al 2022 ). Differently from FD0 and SU25, the daily temperature range (DTR) showed a smaller proportion of negative effects, especially during the winter season.…”

“…Their short-term population trends 2010–2020 (Harris et al 2022 ), for example, highlighted a reduction in population growth rate (European robin) or a weak decline (common blackbird), that might (but it needs to be tested) depend on climate-induced effects. On the contrary, some species could benefit from extreme climatic conditions (Maxwell et al 2019 ), likely due to local adaptations, higher tolerances, ecological plasticity or greater resilience capacity (Renton et al 2018 ; Cooper et al 2020 ; Pipoly et al 2022 ).…”

Comparison of nestling diet between first and second broods of great tits Parus major in urban and forest habitats

“…It is important to note that there may be other effects in the background that we did not assess in this study but that could also reduce nestling survival in the urban habitat. For example, our earlier study showed that the number of hot days can increase nestling mortality (Pipoly et al 2022) and as the season progresses, the frequency of hot days are likely to increase. However, in our study system, we found that the negative effects of hot weather on urban nestlings' body mass and survival were minor or less harmful to nestlings than in forests (Pipoly et al 2022).…”

Interactive effects of rising temperatures and urbanisation on birds across different climate zones: A mechanistic perspective

“…Relatively few empirical studies explore the biotic effects of climate change simultaneously in urban and non‐urban habitats (but see Diamond et al, 2014 ; Zohner, 2019 on phenology; Oliver & Morecroft, 2014 on biodiversity; and Pipoly et al, 2022 on reproduction). Furthermore, none have considered how climate change impacts may differ between cities in different climate types and/or geographical regions.…”