Cold nights leave young barn swallows, small migratory songbirds that build mud nests on buildings, more vulnerable to sickness and death.
Adverse temperatures cause them to be more fragile before they leave the nest, and temperature swings cut growth across their development.
This weather problem affects entire families of birds, where the smallest chicks and least-fed nests can be hit hardest.
Patterns emerge inside nests
At seven breeding sites in Boulder County, north-central Colorado, 113 baby barn swallows were observed during adverse weather, a test of survival before flight…