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Bird reproduction suffers greatly during heat waves

North America is currently facing a significant and rapid decline in bird populations, a situation that has been exacerbated by various factors, including the drastic impacts of climate change. The consequences of rising temperatures on these fragile ecosystems are profound, influencing bird reproduction and survival rates.

Recent findings from a study conducted by researchers from the University of California, Davis, highlight the multifaceted challenges birds encounter and the varying degrees of these challenges depending on their habitats.

Climate impact on bird reproduction

The team illuminated how climate change, particularly the phenomenon of extreme temperatures, affects bird reproduction differently across diverse environments. These revelations are crucial in understanding how combined stressors, such as habitat degradation and climate-induced heat, influence bird populations throughout the United States.

One of the critical discoveries was the detrimental effect of extreme high temperatures on bird reproductive success within agricultural landscapes. Birds residing near farmlands experience a significant reduction in fledgling success during temperature spikes, with their chances of successful reproduction being halved compared to more temperate conditions.

Protective role of forest habitats

Contrastingly, forest environments appear to serve as sanctuaries against the harsh temperatures. The natural canopy cover and shaded areas within these forests contribute significantly to nesting success, thereby offering a crucial climate refuge for various bird species.

Katherine Lauck, the study’s co-lead author and a Ph.D. candidate in ecology at UC Davis, emphasizes the disparity in heat effects between agricultural and forest-nesting birds. She suggests that canopy cover could be a decisive factor in providing much-needed climate refuges, crucial for the survival of diverse bird species that thrive in these habitats.

Urban areas: Unexpected safe havens?

Interestingly, the study found that urban settings, contrary to popular belief, had less negative impact on bird nesting success during heat waves compared to agricultural landscapes. Urban nests, often located in city parks or residential areas with significant tree cover, seemed to benefit from these “mini-forests,” providing a buffer against temperature extremes.

Lauck points out that common cityscapes like backyards and parks could play a vital role as bird habitats, offering a degree of protection against future climate extremes. These findings indicate the importance of urban green spaces for wildlife conservation.

Bird reproduction and citizen science

The project, initiated by Associate Professor Daniel Karp and his students from the Department of Wildlife, Fish, and Conservation Biology, was a response to keep the lab connected during the COVID-19 pandemic. They leveraged data from NestWatch, a citizen science program by Cornell University’s Laboratory of Ornithology.

This large-scale initiative involves volunteers across the country monitoring local bird nests and recording valuable data. The extensive dataset, encompassing over 152,000 nesting records from nearly 60 bird species across various habitats over 23 years, provided a unique insight into bird reproduction trends and the challenges posed by climate change and habitat loss.

The most vulnerable species

The research delved into the species most affected by temperature extremes in agricultural settings. It was observed that the impact was broad, significantly affecting all studied bird species, including western bluebirds and tree swallows, common inhabitants of farms.

The vulnerability was even more pronounced in threatened birds and those that construct open-cup nests, exposing them directly to the elements. According to Karp, the alarming decline in nesting success becomes even more concerning for species already under conservation scrutiny.

Looking ahead: Predictions and conservation

The implications of the study are far-reaching, predicting a further 5% decline in nesting success in agricultural landscapes by 2100 if current greenhouse gas emissions continue unabated. This forecast underscores the urgent need for measures to counteract these effects.

The research advocates for immediate action, such as reducing emissions and creating or preserving natural vegetation patches to serve as thermal refuges. These steps are essential for bird conservation, especially in urban and agricultural settings.

Karp suggests practical interventions, such as strategically placing nest boxes in shaded areas and maintaining native vegetation to provide the necessary cover and protection from heat. These actions could significantly influence the survival of bird populations in the coming years, ensuring these crucial members of the ecosystem continue to thrive.

The full study was published in the renowned journal Science.

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