Breeding and Molt in the White Tern (Gygis alba) on Christmas Island, Pacific Ocean

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Abstract
Sexual and molt cycles of G. alba were investigated by repeatedly examining banded birds with marked feathers, and by recording the events at their nest sites. Breeding occurs at all times of year. Successful sexual cycles take at least 10 1/2 months, but unsuccessful ones are often shorter. The birds start molting, and leave the colony, at about the time they finish feeding, and return to start courtship near the end of their molt. Complete molt takes 5 1/2 to 7 months. The primaries are replaced by a series of simultaneous molt waves, progressing outward about 4 feathers apart. The waves stop when breeding starts, but continue afterwards from the positions they had previously reached. The unusual molt pattern permits growth of several feathers at a time with minimal variation in aerodynamic characteristics. Gygis on Christmas Island have adapted to an environment with little seasonal change by evolving the ability to start a new breeding period as soon as their molt is completed, and also by continuing breeding efforts for a long time if the 1st attempt in 1 breeding period is unsuccessful. Consideration of the kinds of physiological mechanisms that could control lengthy natural molts suggests that in some birds there may be no special internal stimulus for molt, but that feather replacement proceeds except when inhibited by the hormonal state associated with breeding, or by certain other factors. Although the precision of many molt sequences implies that growing feathers are involved in control of the molt of adjacent feathers, it also appears that after producing a feather each papilla tends to become active again automatically after prolonged exposure to a physiological climate permitting molt.