COLONIAL WATERBIRD INVENTORY RESULTS - 1977 



BREEDING ABUNDANCE 



The results from all aerial and ground inventories conducted in 1977 are 

 summarized in Tables 2 through 13. Table 2 shows the order of abundance for 

 all seabirds and wading birds for the entire study area (southern Maine to the 

 Virginia-North Carolina border). Table 3 summarizes nesting populations of 

 the two major waterbird groups in each of the 10 States. Subsequent tables 

 show by State the species nesting in 1977, the numbers of colonies, total 

 pairs, and mean colony sizes. 



The three species of gulls rank 1, 2, and 4 in seabird abundance along 

 the northeast coast (Table 2). This is somewhat expected considering their 

 opportunistic feeding habits, physical dominance of smaller seabirds, and (at 

 least for herring gulls), plasticity in nest and colony site selection (Burger 

 1977). The laughing gull is much more restricted to its nesting habitat than 

 the other two gulls, and concentrates in the salt marshes of southern New 

 Jersey and along the eastern shore of Virginia. Only at small, scattered 

 colonies in Maine and Massachusetts does the laughing gull nest at upland 

 sites. Their current northern populations are a mere remnant of those present 

 in the 1800's in New York (Bent 1963a, Griscom 1923) and during the early 

 1900's in Massachusetts (Nisbet 1971a, b). 



The small number of Arctic, gull-billed, sandwich, and Caspian terns. 

 Leach's storm-petrels, black guillemots, and common eiders were found because 

 they are near range limits, i.e., petrels, eiders, guillemots, and Arctic 

 terns are nearctic species and are more abundant in northern Maine and Canada, 

 while the other species are much more common along the Gulf of Mexico and/or 

 South Atlantic coasts. 



Snowy egrets and black-crowned night herons are the most abundant and 

 widely-distributed of the wading birds. Interestingly, the two recent invad- 

 ing species (cattle egret and glossy ibis) are the next most numerous. Cattle 

 egrets, however, are only common in colonies south of New York. Green herons 

 are much more numerous than indicated in the Table, since only those pairs 

 found in mixed-species heronries are reported. They often nest in small 

 groups or as solitary pairs along the entire coast. The v/hite ibis appears to 

 be expanding its range northward and a pair nested for the first time at 

 Fishermans Island, Virginia in 1977 (P. Frohring pers. comm.). 



State totals of nesting seabirds and wading birds show that Virginia and 

 New Jersey harbor the largest numbers (Table 3), but the relative numbers 

 (density per unit of wetland) are greatest in Rhode Island, New York, and 

 Massachusetts, respectively (Figure 1). Further study is required to deter- 

 mine if these density differences result from nesting habitat and/or food 

 availability differences among States. 



Wading birds comprise the larger proportion of waterbird abundance in the 

 more southern States (Figure 1), probably because of the correlation between 

 wading bird abundance and wetland area (Tables 14 and 15, Custer and Osborn 

 1977). Most wading birds feed predominantly in coastal marshes, pools, and 

 tidal flats; thus, their density is expected to be rriore closely correlated 



