A new study has found that rising temperatures and sudden weather changes are making survival increasingly difficult for baby birds, especially the youngest and weakest chicks inside nests.
Researchers studied 113 barn swallow chicks in Colorado and closely monitored nest temperatures and parental feeding patterns to understand how heat and cold affect their growth.
The findings showed that even small changes in temperature can significantly influence which chicks survive.
Young chicks struggle most in cold weather
Scientists found that newly hatched chicks are highly vulnerable because they cannot regulate their body temperature during the first few days of life.
Without enough warmth from their parents, colder temperatures slowed their growth and reduced body weight.
Researcher Sage Madden explained that young chicks depend entirely on parental care to stay warm until they gradually develop the ability to produce body heat on their own.
Older chicks handled cold conditions better, but extreme heat affected birds of all ages.
Heat causes stress at every stage
The study found that hot weather reduced chick growth regardless of age.
Young chicks struggle because they cannot cool themselves effectively, while older chicks try to regulate body heat by panting, which increases water loss and physical stress.
Researchers also found that large temperature swings between daytime and nighttime created additional challenges, forcing chicks to use energy for survival instead of growth.
Smaller chicks face bigger danger
The study highlighted that the smallest chick in a nest — usually the last to hatch — often faces the greatest risk during extreme weather.
These chicks receive less food and are more sensitive to both heat and cold because of their smaller body size.
Scientists said parental feeding helped chicks cope better with cold weather by providing extra energy, but it offered limited protection against heat stress.
Researchers warned that climate change and increasing heat waves could worsen survival rates for birds such as barn swallows, whose populations are already declining in many regions.