Molt is so demanding that some species actually migrate to different habitat to undergo the process- this is called "molt migration." In 2018, IBP scientists found evidence that molt migration is more common than previously thought
. Many songbirds previously were thought to molt on their breeding grounds, prior to migration. And for many years, the phenomenon of molt migration was thought to occur in just a handful of species.
Our IBP team found evidence that most North American landbirds at least sometimes migrate or disperse to areas separate from the breeding or wintering grounds to molt. This includes species like American Goldfinch; House, Carolina and Pacific Wren; Gray Catbird and Northern Cardinal.
Why move to molt? The most likely explanation is food resources (although this hypothesis has not yet been tested rigorously.) Birds breed in areas where food is abundant early in the summer, when they are courting, laying eggs and feeding chicks. Towards the end of the summer, food resources (like insects) may decrease in these habitats, but increase in others. Birds are very mobile creatures, so they can move to areas where there is plenty of food to fuel the growth of new feathers.
Conserving birds requires understanding their needs across their entire lifecycle. Molt is an important part of that lifecycle and protecting the habitat where birds undergo molt will help conserve populations.
Molting American Goldfinch photo by Rodney Campbell/Flickr.