Meeting Abstract
Molt, or feather growth, is an important part of the annual life cycle of birds. Birds must replace feathers at regular intervals, but considerable variation exists in molt strategy, sequence, and duration. Feather quality and growth rate have been demonstrated to be adversely affected by corticosterone, the main glucocorticoid responsible for the stress response in birds and a key regulator of energy levels and metabolism. CORT has been shown to circulate at the lowest annual levels for many birds during regular periods of molt, perhaps to allow for the growth of good quality feathers. However, periods of molt can occur simultaneously with other life history stages, such as migration or breeding, wherein relatively higher levels for baseline and stress-induced CORT may be adaptive. Here we seek to understand variation in this hormonal association with a life-history trait and, particularly, how such variation is explained by phylogeny and association with other life-history traits. Specifically, we use HormoneBase, a large-scale database of hormone concentrations across vertebrates, to re-examine variation in CORT levels during molt and investigate how life-history traits, such as molt strategy, and phylogeny, explain variation in CORT baseline and stress levels during periods of molt. We predict a greater degree of down-regulation of CORT for birds that have shorter molt period duration and relatively less molt-period overlap with life-history stages in which relatively high CORT may be adaptive. We further predict greater down-regulation of CORT for birds that migrate following molt, as migrants are subject to additional selective pressures favoring quick growth of strong feathers.
