Climate change is causing songbirds to nest earlier in the spring, but the change exposes them to increased temperature shifts, including cold snaps and heat waves. A study from the Cornell Lab of Ornithology found that these extreme weather events cause more birds to fail to nest, especially nestlings.
Nestlings are most vulnerable to extreme temperatures
As temperatures rise due to climate change, many songbirds are nesting earlier in the spring. But this change also brings with it another danger that is especially deadly for chicks: chicks are more susceptible to temperature changes in the form of cold snaps and heat waves. This extreme weather can cause more nestlings to fail to nest. The findings come from a study published today (November 16) in the journal Nature Communications by the Cornell Laboratory of Ornithology.
Effects of temperature changes on nesting success rates
"When we talk about temperature changes, much of the focus is on average temperatures," said co-first author Conor Taff, a researcher in Cornell's Department of Ecology and Evolutionary Biology. "But all living things, including humans, interact with weather conditions in the moment, not with long-term averages. Even if average temperatures don't change, a day or two of extreme cold or heat can pose significant challenges. Changes in average temperatures and variability in temperatures are two different components of climate change."
research analysis
To understand how changing temperatures affect nesting success, researchers analyzed 300,000 breeding bird records submitted by Cornell Lab's NestWatch program between 1995 and 2020. They identified the three coldest and three hottest days in each nest and then studied whether these values predicted lower nesting success. Success is measured by how many chicks survive and fledge.
"We found that 16 of the 24 species we studied had reduced reproductive success when they encountered cold snaps during the hatching or nestling stage. Eleven of the 24 species experienced reduced reproductive success when they encountered heat waves during the breeding season," Taff said. "Aerial insectivorous birds are most sensitive to extreme temperatures, especially low temperatures."
Effects on chicks
The vast majority of bird species feed insects to their young, regardless of what they end up eating, and cold snaps can reduce the supply of insects. If a cold snap occurs when chicks are most vulnerable, it can cause mass mortality. When a cold snap hits, adult birds may move away in search of better living conditions, exposing eggs and chicks to cold and a lack of food.
"Chicklings are really hardest hit because they can't regulate their own body temperature yet," said study co-author Ryan Shipley, a doctoral student at Cornell University. "Chicklings also grow at an exponential rate in the first week or two after birth, and if insect activity is reduced due to a cold snap, the chicks may not survive."
long term consequences
Taaffe and Shipley also looked at 100 years of weather data to see if the timing of cold snaps and heat waves during the March to August breeding season in the United States and Canada has changed. While they found no clear pattern in the timing of extreme temperatures, they did notice that temperatures were getting warmer everywhere.
"Even if chicks survive a cold snap or heat wave, it could have long-term consequences for the bird's overall health," Shipley said. "We're only seeing a brief snapshot early in life and can't measure the long-term health of unzoned wild populations."
Previous studies of tree swallows by these authors have shown that temperature during development is important because it is directly related to the growth rate and body weight of fledglings. This in turn affects their likelihood of surviving, completing their migration, and returning the following year to breed. Thus, changes in temperature and timing of extremes and changes in breeding seasons can combine to have life-changing consequences for individuals and bird populations.