The early nesting caused by the climate poses problems for young swallows

Over the years, we have reported studies showing that certain species of birds adapt to the warming climate by moving their spring breeding season a few days earlier. Now a new study on tree swallows from the Max Planck Institute for Animal Behavior and Cornell University shows the drastic consequences of the shift: Chicks that hatch earlier are at increased risk of bad weather conditions, food shortages and mortality.

The researchers, who examined decades of data on weather, food availability, and breeding in tree swallows, say the timing of when to breed and when to get food is decoupled for some animals – highlighting the complexity behind how wild living animals respond to climate change.

“Moving data earlier to track climate change is not necessarily risk-free,” says Ryan Shipley, a postdoctoral fellow at the Max Planck Institute for Animal Behavior and first author of the paper published in PNAS. “Riskier conditions earlier in the year can expose animals to unintended consequences if they respond to bouts of unusually warm spring weather.”

Weather shifts affect insect prey

Shipley and co-authors found that tree swallows had advanced breeding three days every three years for the past 30 years, but offspring hatched earlier were at greater risk of exposure to inclement weather, which in turn decreased the availability of the flying insects which they rely on for food.

“Our results increase the possibility that animals that rely on food resources that can change rapidly due to weather abundance are at particular risk for climate change,” says Shipley.

The study uncovered strong fitness consequences for birds, which are advancing breeding at a rate similar to climate change. But there may also be clues to the mystery of why insectivorous airbirds such as swallows, swifts, flycatchers and night owls are declining faster than other groups in much of North America and Europe.

Spring weather can change quickly and is rather unpredictable at the beginning of the year. The activity of flying insects is determined by the weather, which means that they are available stochastically.

“For birds that feed on flying insects, one day is a festival, the next a famine. This means that in unusually warm springs, parents rely on current conditions that result in earlier oviposition, which suggests similarly good conditions for hatched young people three weeks into the future, ”says Shipley.

The results reveal a previously unobserved threat to insectivorous airbirds. “Considerable attention has been given to the potential widespread decline in insect populations, and this could hit insectivorous birds particularly hard. However, we show a mechanism that does not require a change in insect abundance – only availability for a short time, such as a few days. “

Thank you Cornell University for providing this news.

Birds and Climate Change in the Last Decade

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