CAN MIGRANTS DO IT FASTER? ACCELERATED MOLT OF BAIRD'S SPARROWS AND FURTHER INSIGHTS INTO SOUTHWESTERN MOLTING GROUNDS
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Using museum specimens, I document the prebasic flight-feather molt and molting grounds of Baird's Sparrow (Ammodramus bairdii). Prebasic molt can apparently be carried out to some extent during fall migration. When initiating or completing molt, most Baird's Sparrows appear to be concentrated at the northern edge of their wintering range, and well within the late-summer monsoon zone. This staging may be to make use of the monsoon zone, broadly defined, but also to avoid the heavier monsoon rains found farther south in the wintering range. During prebasic molt, adult female Baird's Sparrows replace their primaries in 27 days, whereas adult males take 46 days; the mean replacement time is 39 days when sexes are combined. This is the fastest rate yet reported for a western U.S. breeding passerine, and I hypothesize that it might be due to being released from energetic constraints im posed by additional extensive migration.
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