|dc.description.abstract||The ecology of field-feeding dabbling ducks wintering on the Southern High Plains of Texas was studied on a 50 km2 study area in Castro County, from September-March 1979-82. Ducks relied primarily on waste corn that averaged 364 j^ 12 kg/ha/field. Fields harvested at 14-21^ moisture lost more than twice the corn as fields harvested at 22-36^ moisture. Therefore, moisture content of corn at harvest provided a useful measure to predict initial waste. Waste cornfields underwent a variety of agricultural treatments that affected the abundance and availability of waste corn to waterfowl. Burning stubble maximized abundance and availability, whereas deep plowing reduced abundance by 975o. Disking and grazing reduced abundance by 77^ and 84-%, respectively. However, landowners tended to graze cattle on fields where initial waste was high and thus substantial amounts of waste corn remained when grazing was terminated. Manual salvage by migrant workers removed 58% of initial corn waste.
Field-feeding waterfowl conducted 2 flights daily to cornfields near playa lakes where the birds concentrated. The average morning flight was initiated 52 j^ 1.5 min before sunrise and terminated in 23 _+ 1 .4 min. The average evening flight began 25 j^ 2.0 min after sunset and terminated in 37 j^ 4.2 min with duration increasing as the season progressed.
Dabbling ducks fed longer and participated more in evening as compared to concurrent daily morning flights. Minimum temperatures were correlated negatively with duration of evening flights, but not morning flights. There was no correlation between the amount of waste corn in, or the condition of, a field selected by feeding ducks with duration or initiation of feeding flights. However, the amount of corn present was correlated negatively with duration of the evening flight. Snowfall was positively correlated with duration of evening flights, but not morning flights.
Feeding flocks selected fields based on an abundance/availability hierarchy, apparently attempting to minimize foraging time. Eurned fields were preferred most when available, followed by disked fields, especially those containing >60 kg waste corn/ha. Field-feeding is an adaption to widespread agriculture, but also is a learned response to changes in wetland habitats.||