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How do young swifts survive when bad weather limits insect food?

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Illustration of a chestnut-collared swift (Cypseloides rutilus) in flight, showing its dark brown body and wings with a distinctive reddish-brown collar around its neck. — Apodiform Chestnut-collared swift (*Cypseloides rutilus*)

When bad weather limits the availability of flying insects, young swifts survive by entering a state of energy conservation. During these periods, they are often left unbrooded for hours, and their body temperature is allowed to drop to near that of the environment.12

This essentially poikilothermic (cold-blooded) condition slows the young birds' development and helps them conserve vital resources until food becomes more plentiful. While this would typically lead to chilling and potential death in many other bird species, it is a natural survival mechanism for young swifts. Additionally, some species, such as those in the genus Cypseloides, develop a coat of downlike semiplumes that aids in thermoregulation during these times.12