A study of waterfowl habitats, populations and fluctuations in the lower Trinity River and the upper Trinity Bay, Texas

Waterfowl habitats, populations, and fluctuations were studied, from 1966 to 1971, in a 20,000 acre marsh on the Texas Gulf Coast. The marsh was type-mapped and 5 major vegetation zones were designated: 1) intermediate marsh; 2) saltwater marsh; 3) freshwater marsh; 4) wooded swamp; 5) controlled waterlevel salt marsh. A total of 55 plant species occurred on the study area. Paspalum lividum was the major species constituting 27.8 percent of the vegetative composition. Major species of the vegetation zones were Paspalum lividum in zones 1, 2, and 5; Alternathera philoxeroides in zone 3, and Phyla lanceolata in zone 4. Coefficients of similarity, calculated for comparison of vegetation zones, ranged from 0.0 to 0.366. Soil salinity and pH values indicated an increase in salinity and acidity as sampling approached Trinity Bay. Waterfowl were observed every month, with February and October contributing the largest numbers, and June and July the smallest. No waterfowl nests were found, but 1 wood duck and 6 mottled duck broods were observed. Analysis of mean waterfowl numbers showed some significant and highly significant differences between months, vegetation zones, and waterfowl groups. Food habits for 371 waterfowl collected were determined. Plant materials comprised 100 percent of the total food volume of geese. Native grasses composed 80.9 percent of the total volume and were the most important food item consumed. Other marsh plants represented 18.6 percent, and cultivated rice (Oryza sativa) contributed only 0.5 percent. Fourteen duck species analyzed to determine dietary patterns. Plant materials comprised 87.5 percent of all foods, while animal matter made up 12.5 percent. Cultivated rice was the most important plant food, representing 31 percent of the total food volume. Indices of similarities computed for duck food habits ranged from 0.154 to 0.749 and were used to differentiate the ducks into 3 divisions.