The suitability of wading birds (herons and their allies) as biological indicators in the coastal environment were studied in 1975 by 8 teams of investigators which located and censused 198 colonies along the Atlantic coast from Maine to Florida [USA]. Over 1/4 million breeding birds [Ardea herodias, Butorides virescens, Florida caerulea, Bubulcus ibis, Dichromanassa rufescens, Casmerodius albus, Egretta thula, Hydranassa tricolor, Nycticorax nycticorax, Nyctanassa violacea, Mycteria americana, Plegadis falcinellus, Eudocimus albus and Ajaia ajaja] were censused. The number of species in colonies ranged from 1-11. The number of 1- and 2-spp. colonies increased from Florida to Maine. Colony size decreased from Florida to Maine. Wading bird colony sites are generally active each year and the number of colonies may have recently increased in some areas of the coast. Species composition and total population of colonies fluctuate from year to year. The breeding population of wading birds was correlated with the area of coastal wetlands by state. Five teams of investigators studied the reproductive biology of 9 spp. in 13 colonies. Mean clutch size, the percentage of nests in which 1 or more eggs hatched and the overall percentage of eggs that hatched differed among colonies for some species, but no latitudinal gradient was found in any of these characteristics for any species. The use of wading birds to their full potential as biological indicators requires further exploration: survey and reproductive success methods need to be tested, the survey of colonies repeated, available historical information assembled and habitat requirements measured.
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Wading birds as biological indicators 1975 colony survey