NESTING ECOLOGY OF ROSEATE SPOONBILLS AT NUECES BAY, TEXAS

We conducted a study in 1978-1980 of the nesting colony of Roseate Spoonbills (Ajaia ajaja) in a relatively polluted environment at Nueces Bay, Texas. For 154 marked nests, the average clutch size was 3.0 eggs; 73% of the eggs hatched, and 87% of the nests were successful ( hatched at least 1 young). The average nest successrate (total fledglings:total eggs) was 50% or 1.5 fledglings per total nests. Incubation began the day after the first egg was laid, and the incubation period for each egg was 22 days. Eggs hatched in the order that they were laid; the first and second eggs hatched on consecutive days, and the second, third, and fourth eggs hatched every other day. Nest composition and size were highly consistent, but nest placement varied considerably and was dependent on the vegetative configuration of the dredge-material islands. Growth rate of nestlings conformed to a ‘standard’ growth curve, where body weight of nestlings at fledging equaled that of adults. There was no difference in weight gain among siblings based on actual age. Nestlings fledged at about 6 weeks of age, when feather development was complete. At fledging, the bills of juveniles had almost reached adult width, but bill length was only 67% that of adults. In general, environmental pollutants were low (<2 ppm) in spoonbill eggs, though a few eggs contained elevated concentrations of DDE (up to 15 ppm, wet weight). Some eggshells were 5% thinner than those in museum collections, but the degree of thinning was not within the range known to cause population declines. We conclude that organochlorine pollutants are not adversely affecting spoonbill reproduction at Nueces Bay, Texas, though the area is surrounded by industries and agricultural land. A parently, spoonbills are less sensitive to these contaminants than are other aquatic species.

DONALD H. WHITE, CHRISTINE A. MITCHELL, EUGENE CROMARTIE, The Auk 99: 275-284