LONG-TERM POPULATION TRENDS OF COLONIAL WADING BIRDS IN THE SOUTHERN UNITED-STATES - THE IMPACT OF CRAYFISH AQUACULTURE ON LOUISIANA POPULATIONS

Long-term population dynamics of colonial wading birds (Ciconiiformes) were examined using data from Audubon Christmas Bird Counts (CBC, 194 9-1988) and Breeding Bird Surveys (BBS, 1966-1989). Winter populations of Louisiana wading birds increased dramatically over the 40-year per iod, with the sharpest increases occurring during the last 20 years. S everal species populations grew exponentially from 1968 to 1988. High overall positive covariance was found in the abundance of the various species over time, and cluster analysis showed that the species with s imilar dietary requirements and foraging habits covaried most strongly and positively with each other. Trend analysis of CBC and BBS data fr om 1966-1989 and 1980-1989 showed a close correspondence between CBC a nd BBS trends in Louisiana. Most species increased in Louisiana at the same time as they declined in Florida and Texas. Several factors migh t explain increases in populations of wading birds in Louisiana, inclu ding long-term recovery from the effects of human exploitation, expans ion of breeding populations in more northern states, changes in weathe r, recovery from DDT and similar pesticides, and regional movements du e to habitat loss in other coastal states. These hypotheses are not mu tually exclusive and merit further study. However, based on several in ferential lines of evidence, increased acreage devoted to crayfish (Pr ocambarus) aquaculture in Louisiana appears to be the most significant factor explaining observed population trends in the state. First, pop ulations of colonial wading-bird species that use crayfish were correl ated positively with the wild crayfish harvest in Louisiana, and even more strongly with commercial crayfish pond acreage. Second, the regul arity with which these ponds are managed provides a more predictable f oraging habitat than do corresponding natural areas. Third, the use of crayfish ponds by wading birds peaks during pond drawdowns, which may increase reproductive success by concentrating prey available to wadi ng birds during their nesting season. Fourth, those species of wading birds that specialize on crayfish showed the greatest population incre ases and the strongest correlation with crayfish pond acreage. These f indings have important implications for conservation and management of Louisiana's wading-bird populations.