Out Ln'tiif^ Rt'siHiiVi's — BtrJs 



5.1 



Colonial walerbirds. that is, scabirds (gulls, 

 terns, cormorants, pelicans) and wading 

 birds (herons, egrets, ibises), have attracted the 

 attention of scientists, conservationists, and the 

 public since the turn of the century when plume 

 hunters nearly drove many species to extinction. 

 The first national wildlife refuge at Pelican 

 Island, Florida, was founded to conserve a large 

 nesting colony of the brown pelican {Pclccaniis 

 occidentalis). The National Audubon Society 

 also established a game warden system to mon- 

 itor and protect important waterbird colonies. 

 These efforts helped establish federal laws to 

 protect migratory birds and their nesting habi- 

 tats in Noilh America. 



Although the populations of many species 

 rebounded in the early part of the 2()th century, 

 major losses and alteration of coastal wetlands 

 still threaten the long-term sustainability of 

 many colonial waterbirds. A national, coordi- 

 nated monitoring program is needed to monitor 

 population status and trends in colonial water- 

 birds (Erwin et al. 1993). The Canadian 

 Wildlife Service has recently established a 

 national seabird monitoring program (D. 

 Nettleship. CWS, personal communication). In 

 addition, better coordination and cooperation 

 for monitoring waterbirds are needed on both 

 their breeding grounds in North America and 

 their wintering grounds in Latin America where 

 wetland loss is also a critical problem (Erwin et 

 al. 1993). This article summarizes the status 

 and trends of selected waterbird species in 

 North America, but excludes Alaska. Hawaii, 

 and the Pacific coast, which are described else- 

 where. 



Population Surveys 



Data on the population status of coloni; 

 waterbirds come from many sources. The 

 Breeding Bird Survey (Peterjohn and Sauei 

 1993) is useful as a visual index for the more 

 widely distributed species that occur along 

 coasts and across the interior of the United 

 States and Canada (e.g.. great blue herons 

 [Ardea herodias] and herring gulls [Larus 

 cirgentalus]). but it is not effective for many 

 waterbird species that nest in wetlands. 



Recently, Christmas Bird Count (CBC) data 

 have been analyzed, providing an index to num- 

 bers of wintering birds (J.R. Sauer, National 

 Biological Service, personal communication). 

 For waterbirds, these counts must be used with 

 caution since water conditions can have a major 

 effect on the feeding distribution of waterbirds 

 during the count period in December. Thus, 

 trends in CBC counts may indicate more about 

 trends in wetland conditions than trends in pop- 

 ulations of any particular waterbird species. 



More precise estimates of species" popula- 

 tions at colony sites have been conducted over 

 the years by state, federal, and private organiza- 

 tions. Although a few states (e.g., Florida, 

 Illinois, Massachusetts, Texas, and Virginia) 

 have conducted annual surveys over a long peri- 

 od for at least some species, there is little con- 

 sistency among their methods and the frequen- 

 cy of surveys (Erwin etal. 1985). Many data on 

 breeding populations are kept at the state level, 

 but these data seldom predate 1 980. precluding 

 assessment of long-term trends in many of these 

 long-lived species. 



Even though more than 50 species of colo- 

 nial waterbirds breed in the United States, 

 Canada, and Mexico, this article focuses on the 

 22 species for which sufficient data are avail- 

 able to indicate population changes, at least at a 

 regional level. 



Pelecaniformes 



Pelicans and their allies (cormorants, anhin- 

 gas) suffered from DDT use, and their numbers 

 plummeted to the point where the eastern and 

 California brown pelicans became endangered. 

 The eastern subspecies, however, was recently 

 removed from the threatened list because of its 

 rapid numerical and range increases (Table). 



The American white pelican {Pelecamis eiy- 

 throrhynchos) has shown similar sharp increas- 

 es in the western regions of Canada and the 

 United States (Evans and Knopf 1993). Double- 



Colonial 

 Waterbirds 



by 



R. Michael Erwin 



National Biological Service 



Common tern (Sterna hinindo). 



