Wintering diving duck use of coastal ponds: An analysis of alternative hypotheses

Gulf Coast estuaries provide food for wintering diving ducks, but little is known of the resources provided by adjacent coastal ponds. We determined wintering redhead (Aythya americana) and lesser scaup (A. affinis) activity budgets (1988-89) and habitat characteristics (1987-88 and 1988-89) in southern Texas to test alternative hypotheses explaining coastal pond use. Both species spent more (P < 0.05) time drinking and preening in ponds and more (P < 0.05) time feeding and moving in estuaries. Activity budgets of both species varied diurnally and monthly in ponds (P < 0.05), but few changes in rank of activities occurred. Ponds used by redheads and lesser scaup had lower salinities (less than or equal to 15 ppt), deeper water (> 10 cm), and were closer to estuarine feeding sites than ponds not used (P < 0.05). Activity budgets and pond resource use of both species were consistent with predictions of the dietary freshwater hypothesis, but contradicted predictions of the alternate food and disturbance hypotheses. Estuaries provide seagrass and invertebrate foods while adjacent coastal ponds provide dietary freshwater; both are essential components of diving duck winter habitat along the Gulf Coast. Based on our results, further research is needed to assess alternative physiological effects of osmoregulation through nasal salt glands versus dietary freshwater.