A recent study by the Cornell Lab of Ornithology, published in the journal Nature Communications, reveals that many songbirds are nesting earlier in spring due to warmer temperatures caused by climate change. However, this shift exposes them to temperature variability, including cold snaps and heat waves, which can be particularly deadly for nestlings and result in more nest failures.
Temperature changes reduces nesting success
Co-lead author Conor Taff, a researcher in Cornell University’s Ecology and Evolutionary Biology Department, emphasized that while discussions about temperature changes often focus on averages, it’s the immediate weather conditions that all creatures, including humans, interact with. Even a one or two-day period of extreme cold or heat can pose significant challenges.
The researchers analyzed 300,000 breeding bird records submitted to the Cornell Lab’s NestWatch project between 1995 and 2020. They identified the coldest and hottest three-day periods for each nest and examined whether these extremes predicted lower nesting success.
The study found that 16 of the 24 species studied had reduced reproductive success when a cold snap occurred during the incubation or nestling stages, and 11 of 24 had reduced success when a heat wave occurred during the breeding season.
The researchers also found that the majority of birds feed insects to their young, and cold snaps reduce insect availability. If these episodes occur when nestlings are most vulnerable, they can trigger a mass die-off. During a cold snap, adult birds may move away to find survivable conditions, leaving eggs and nestlings exposed to cold and lack of food.
One notable observation is the impact of cold snaps and heatwaves on breeding attempts. The study identifies 11 out of 24 species experiencing reduced fitness during cold snaps, particularly aerial insectivores heavily reliant on flying insects for food. In contrast, all species in the dataset demonstrated vulnerability to heatwaves.
Impact of Climate Change on Birds
The researchers also examined 100 years of weather data to see if there have been changes in the timing of cold snaps and heat waves during the March through August breeding season in the United States and Canada. Although they found no clear pattern in the timing of temperature extremes, they noted that it’s getting warmer everywhere.
The study highlights the pressing need to understand and mitigate climate change’s effects on bird populations and their ecosystems. Its findings offer insights for conservation strategies in an era of escalating climate change impact.
While the average spring temperature anomaly showed a consistent positive trend over the years, the study found that the timing and intensity of cold snaps and heatwaves varied significantly. Contrary to expectations, the date of the last cold snap tended to occur 3 to 5 days earlier, while the first heatwave did not consistently differ from historical averages.
The study examines how climate fluctuations affect bird species’ reproductive success. Cold snaps during incubation significantly affected several species’ fitness, including 8 out of 24 species like purple martins and eastern bluebirds. No species showed improved fitness due to extreme temperatures.
The research further examined latitudinal trends in temperature exposure and susceptibility for specific bird species, such as eastern bluebirds, purple martins, and tree swallows. Results highlighted variations in the impact of cold snaps and heatwaves at different latitudes, emphasizing the need for a nuanced understanding of climate change effects on diverse bird populations.
Climate Variability affects Bird Reproduction
The analysis of community-contributed breeding records sheds light on the intricate relationship between climate variability and the reproductive success of North American bird species. The study, based on data spanning 1995 to 2020, reveals that exposure to three-day cold snaps during breeding attempts is linked to reduced relative fitness in a significant portion of common species.
Surprisingly, exposure to three-day heatwaves also affects the fitness of various species, although the impact is less widespread compared to cold snaps. Of the 24 common species studied, 11 showed reduced fitness in the face of heatwaves. The spatial heterogeneity in sensitivity to temperature extremes suggests that climate change could drive population trends that differ across the range of a species.
The study questions assumptions about consistent shifts in cold snaps and heatwaves timing over the past 70 years. Despite rising average spring temperatures, extreme events’ dates haven’t consistently shifted, highlighting the complexity of climate change impacts on wildlife.
The study highlights that changes in breeding phenology alone may not sufficiently capture the effects of climate change. The incomplete shifts in breeding timing observed in response to average temperatures may be inadequate to keep pace with the challenges posed by temperature variability.
The results highlight the importance of considering both average temperature and temperature variability to accurately predict the vulnerability of bird populations to climate change.
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