| Summary: | Waterfowl may spend more time on wintering grounds than at any other location during their annual cycle. The Southern High Plains of Texas (SHP) are an important wintering area for Central Flyway waterfowl. Up to one million waterfowl use the SHP during winter including as many as 300,000 northern pintails (Anas acuta). This study investigated 1) nutrient reserve dynamics of wintering northern pintails, 2) models of condition for wintering northern pintails, 3) condition and diet biases associated with hunter-killed northern pintails and 4) molt patterns of wintering northern pintails. Total precipitation was 58% higher in 1985-86 than in 1984-85 (April through March periods). Body, fat and gizzard weights and percent fat were higher in the wet year (1985-86). Age classes (adult and immature) did not differ with the exception of ash weight. Males had higher body, protein (ash-free lean dry), ash, gizzard and liver weights than females. Percent fat was higher for females. Changes in nutrient levels may be endogenously regulated to increase survival during stressful periods of the annual cycle. Changes in gizzard weight probably reflect changes in diet (fiber content) between years and across the wintering period. Pair status was not consistently associated with an improvement in nutrient reserve status. A threshold of condition may regulate timing of pair bond formation. Initiation of courtship and pair bond formation were advanced in the wet year. Four models of condition were developed for wintering northern pintails. Models explained more than 65% of the variation in their dependent variable (fat weight, the logarithm of fat weight or a condition index incorporating fat weight) in all cases. All models accounted for greater than 70% of the variation in fat weight in the validation data set. Bias was low and negative. Aggregate percent volume and aggregate percent dry weight of all plant foods except green material differed between decoy-shot (huntershot) and jump-shot northern pintails. Corn was more prevalent ...
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