Birds are among the most diverse and fascinating animals on Earth. They play important roles in ecosystems, providing services such as pollination, seed dispersal, pest control, and nutrient cycling.
They also have cultural, aesthetic, and recreational values for humans, inspiring art, literature, music, and tourism.
However, birds are also facing many threats from global change, such as habitat loss, pollution, invasive species, disease, and climate change.
One of the effects of climate change on birds is the increase in frequency and intensity of heat waves, which can have negative impacts on their reproduction and survival.
The impact of extreme temperatures on avian reproduction
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Bird populations are in rapid decline across North America. While climate change is just one of the many factors influencing North American birds, its effects are significant and can interact with other stressors, such as habitat loss.
A team at the University of California, Davis, researchers found that the effects of extreme temperatures on avian reproduction can vary depending on the type of environment that birds call home.
The findings, published in the journal Science, shed light on how climate change can combine with habitat loss to affect bird reproduction across the United States.
Researchers found that extremely high temperatures significantly diminish bird reproductive success in agricultural landscapes.
Birds nesting near farmland were half as likely to have at least one fledgling successfully leave the nest when temperatures spiked.
The researchers analyzed data from NestWatch, an initiative created by Cornell University's Laboratory of Ornithology, where people from across the country monitor bird nests near them and use an app to record information on types of bird species, nest locations, number of eggs laid, baby bird activity and more.
They looked at more than 152,000 nesting records featuring nearly 60 bird species that were nesting in farms, forests, grasslands and developed areas across the country during the span of 23 years (1998-2020).
They found that heat waves had a negative impact on nesting success for most bird species, especially those that breed in open habitats like grasslands and farmlands.
For example, western bluebirds and tree swallows had lower nesting success when temperatures exceeded 35°C (95°F) in agricultural areas.
The researchers estimated that heat waves reduced the number of fledglings produced by these two species by about 10% each year.
However, not all habitats were equally affected by heat waves. The researchers found that forests seemed to provide a protective buffer against high temperatures, offering shaded areas that helped increase nesting success.
For instance, wood thrushes and eastern bluebirds had higher nesting success when temperatures exceeded 35°C (95°F) in forested areas.
The researchers suggested that canopy cover probably constitutes an important climate refuge for birds that can thrive in various habitats.
When they looked at how heat waves affected nesting success in urban areas, the researchers found less of a negative impact than in agriculture, probably because nests were often in city parks and residential areas that can have high tree cover.
They said that places like backyards and parks may provide important bird habitat that is somewhat more buffered from climate extremes in the future.
The researchers also noted that some bird species may have behavioral or physiological adaptations that allow them to cope with high temperatures better than others.
For example, some birds may adjust their timing of breeding, nest site selection, or parental care to avoid heat stress.
They said that more research is needed to understand how different bird species respond to heat waves and how they may adapt to future climate scenarios.
The study highlights the importance of considering both climate and habitat factors when assessing the impacts of global change on biodiversity.
Furthermore, the researchers said that their findings can help inform conservation strategies for birds and other wildlife in a warming world.
Protecting and restoring natural habitats, especially forests, can help buffer the effects of heat waves and provide suitable nesting sites for birds.
Moreover, promoting urban greening and reducing greenhouse gas emissions can help mitigate climate change and its consequences for birds and humans alike.
