Wading birds as biological indicators: 1975 colony survey.




Custer, T.W.
Osborn, R.G.

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U.S. Department of Interior, Fish and Wildlife Service.


In 1975 we studied the suitability of wading birds (herons and their allies) as biological indicators in the coastal environment. Eight teams of investigators located and censused 198 colonies along the Atlantic coast from Maine to Florida. Fourteen species including over one-quarter million breeding birds were censused. The number of species in colonies ranged from 1 to 11. The number of one- and two-species 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. Both species compostition 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 nine species in 13 colonies. Mean clutch size, the percentage of nests in which one 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.


28 p.


herons, indicators, population number, population dynamics, breeding sites, wetlands, waterfowl, reproduction