Food and Resource Utilization by Wintering Redheads on Lower Laguna Madre

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Abstract
The food choice of wintering redheads (Aythya americana) and their exploitation of available food resources were investigated during 1974-1975 on Lower Laguna Madre, Texas, [USA]. Fall standing crop (dry weight) of the dominant submergent shoalgrass (Halodule beaudettei) was estimated to be 19,290 metric tons from a systematic random sample of a 23,875 ha study area, a yield of 820 kg/ha. Estimated biomass of shoalgrass for the entire bay was 30,300 metric tons. Manateegrass (Syringodium filiforme) and gulf halophila (Halophila engelmanni) occurred less frequently. Resampling in spring demonstrated a significant but spatially uniform reduction in shoalgrass standing crop to 15,548 metric tons. Dominant mollusks in fall samples were Tellina sp., Cumingia tellinoides and Tagelus plebeius. Redheads were distributed primarily in shallow water over hard sand substrate vegetated exclusively by shoalgrass. Shoalgrass comprised 71% of the diet of 19 redheads. Mollusk utilization was considered insignificant. Captive redheads consumed 77.5 g/bird per day of commercial game bird ration and natural food. Exploitation of fall shoalgrass was determined from regular censuses of redheads during the winter of 1974-1975. From late Oct. to late March, 9,917,800 bird-day units were recorded in relation to an estimated total consumption of 770 metric tons of shoalgrass. Redheads consumed 4% of the fall standing crop and accounted for 21% of the winter decrease in shoalgrass biomass.

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