… They stop the molt of their flight feathers just before migration …
This is from Ornithology, Third Edition by Frank B. Gill (2007):
… The complete molt is a major undertaking. The bird sheds and then regenerates thousands of feathers, roughly from 25 to 40 percent of its lean dry mass (i.e., excluding fat and water content). Molt draws significantly on protein and energy reserves to synthesize feather structure and to offset the costs of poorer insulation and flight efficiency.
… Tropical terns such as the Angel Tern on Christmas Island turn the molt on and off to breed whenever possible. This delicate seabird has no pigment in its flight feathers, which consequently wear easily and must be replaced more often than those of most other terns.
[line break added] Wave after wave of molt is initiated in the flight feathers, The innermost primaries often begin to molt again before the outermost primaries are replaced in the preceding molt. As many as three successive molts may be in progress simultaneously.
[line break added] When an Angel Tern starts to nest (it simply lays an egg precariously on a bare branch), the molt stops suddenly, no matter which feathers may be missing — the molting equivalent of musical chairs. After the tern has finished nesting, molt resumes as if there had been no interruption in the complicated pattern of feather replacement.
… Renesting White-crowned Sparrows molt so fast at high latitudes that they become almost flightless for a short time. Peregrine Falcons and American Golden Plovers, as well as many other shorebirds, begin their molts on their Arctic breeding ground but are unable to complete the process in time to leave for the south. They stop the molt of their flight feathers just before migration and then resume it for several more months after reaching their wintering grounds.
My most recent previous post from Gill’s book is here.
-Julie
Coloring 