Coastal Pond Use by Redheads Wintering in the Laguna Madre, Texas.

The distribution of North American redheads ( Aythya americana) during winter is highly concentrated in the Laguna Madre of Texas and Tamaulipas, Mexico. Redheads forage almost exclusively in the lagoon and primarily on shoalgrass ( Halodule wrightii) rhizomes; however, they make frequent flights to adjacent coastal ponds to dilute salt loads ingested while foraging. We conducted 63 weekly aerial surveys during October–March 2000–2003 to record use of coastal ponds by redheads. We collected information from used and unused coastal ponds to better understand factors selected by redheads for their dietary fresh water requirements. Coastal ponds used by redheads had greater surface area, percent open water, average depth, and turbidity than unused coastal ponds. Similarly, redheads used coastal ponds with lower salinity and ammonia concentrations than unused ponds. Redheads were observed on coastal ponds >6 km from foraging areas on 95% of surveys during dry conditions in 2000–01, compared to 43% of surveys during moderately wet conditions in 2001–02 and 5% during very wet conditions in 2002–03. Finally, our data suggests that redheads rely on dietary freshwater sources throughout winter and do not reduce visitation to these coastal ponds as winter progresses. [ABSTRACT FROM AUTHOR]