| Summary: | Abundance of the northern pintail (Anas acuta) has remained below long-term average population levels and well below population objectives established by the North American Waterfowl Management Plan. A large proportion of pintails in the Central flyway winter along the Texas coast where changes in land use over the last few decades have greatly reduced the capacity of the region to support wintering pintail populations. I collected 344 female pintails (164 adults, 180 juveniles) during October-March of 2012-2015 on the central and upper Texas coast. In order to examine the influence of these land use changes on pintails, I estimated trends in their body composition, gut morphology, molt chronology and molt intensity. Adult and juvenile females wintering on the central Texas coast exhibited larger declines in masses of lipids and protein than did those wintering on the upper coast. Those masses typically reduced in juveniles early in winter, but by late winter were similar to adults. Total digestive tract length declined in early winter then increased toward mid-winter through spring as a result of changes in small intestine and gizzard lengths in adult females. Additionally, digestive tract mass declined in early winter then increased due to changes in mass of upper digestive tract, small intestine, gizzard, and liver. There was no evidence of an effect of somatic protein on total molt intensity. I detected no trend in number of molting feathers during winter in adult pintails, but I did in juveniles during year 1. This research highlights the importance of high-quality foraging sites for pintails, especially late in winter on the Texas coast.
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