HABITAT USE BY PISCIVOROUS BIRDS ON A POWER-PLANT COOLING RESERVOIR

Densities of piscivorous birds were compared among habitats on a Texas reservoir with warm-water effluent. The reservoir had been invaded recently by the exotic submergent hydrilla (Hydrilla verticillata). Hydrilla was an important habitat for some piscivores, particularly Pied-billed Grebes (Podilymbus podiceps) and also cormorants (Phalacrocorax spp.) and American White Pelicans (Pelecanus erythrorhynchos). Wading bird (Ardeidae) densities were low in hydrilla and highest in the emergent-hydrilla interface, unvegetated shoreline/shallow water and emergent habitats. Density comparisons between the main body of the lake and an associated cooling pond with higher water temperatures did not demonstrate consistent patterns across species or seasons. Overall piscivore densities were higher in the hot lake; this was largely due to high densities of Great Blue Herons (Ardea herodias) and cormorants. For many piscivores, neither the presence of hydrilla nor warm-water effluent influenced habitat use.