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Diurnal time-activity budgets were determined for wintering redheads (Aythya americana) from estuarine seagrass beds in Louisiana (Chandeleur Sound) and Texas (Laguna Madre) and from ponds adjacent to the Laguna Madre. Activities differed (p<0.0001) by location, month, and diurnal time period. Resting and feeding were the most frequent activities of redheads at the two estuarine sites, whereas drinking was almost nonexistent. Birds on ponds in Texas engaged most frequently in resting and drinking, but feeding was very infrequent. Redheads from the Louisiana estuarine site rested less than birds in Texas at either the Laguna Madre or freshwater ponds. Redheads in Louisiana fed more than birds in Texas; this was partially because of weather differences (colder temperatures in Louisiana), but the location effect was still significant even when we adjusted the model for weather effects. Redheads in Louisiana showed increased resting and decreased feeding as winter progressed, but redheads in Texas did not exhibit a seasonal pattern in either resting or feeding. In Louisiana, birds maintained a high level of feeding activity during the early morning throughout the winter, whereas afternoon feeding tapered off in mid-to late-winter. Texas birds showed a shift from morning feeding in early winter to afternoon feeding in late winter. Males and females at both Chandeleur Sound and Laguna Madre showed differences in their activities, but because the absolute difference seldom exceeded 2%, biological significance is questionable. Diurnal time-activity budgets of redheads on the wintering grounds are influenced by water salinities and the use of dietary fresh water, as well as by weather conditions, tides, and perhaps vegetation differences between sites. The opportunity to osmoregulate via dietary freshwater, vs. via nasal salt glands, may have a significant effect on behavioral allocations.

Composition and biomass of beds of submerged aquatic vegetation (SAV) in estuaries along the upper Texas coast were examined from bottom core and rake samples taken along 72 line transects during July-August 1987. Substrate composition, salinity, water depth, and water clarity were also measured at each sample station. Halodule wrightii was the dominant species of SAV meadows (69% occurrence), followed by Ruppia mart'tima (36%). Najas guadalupensis and l~dlisneria americana were only found in the shallow (<60 era), oligohaline (< 10 ppt) waters of Trinity Bay. Halophila engelmannii and Thalassia testudinum were only found in the deeper (35-110 cm) euhaline waters (30--40 ppt) of Christmas and Matagorda Bays. H. wrightii and R. maritima occurred across the greatest depth and salinity spectra, with R maritima more prominent in shallower (<90 era) mixohaline waters (10-30 ppt) and H. wrightii more prominent in euhaline waters (30--40 ppt). Beds of SAV were more extensive and had greater biomass along south shorelines compared to north shorelines (P < 0.045), and depth to which vegetation grew was positively correlated with water clarity (r = 0.927, P < 0.001). The correlations of water depth, salinity, and water clarity with variation in SAV species composition and distribution suggest that abiotic tolerances documented by previous experimental studies are major factors influencing field distributions. Comparisons with similar field data from the early 1970s corroborate the reported decrease in SAV in the Galveston Bay complex and suggest a slight increase in the Matagorda Bay complex, Decline of SAV in the Galveston Bay complex coincided with major shorefront development and a decline in numbers of wintering redhead ducks Aythya americana.Protection of shorelines of upper coast estuaries is vital to maintaining SAV resources and the dependent fauna. Where possible, barrier island preserves should be established adjacent to beds of SAV and development restrictions implemented to reduce impacts.

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