nested on higher vegetated parts of the islands, whereas herring gulls often 

 nested seaward from vegetated areas and among storm-tide debris. The eggs 

 of black-backs are larger and the nestlings are more buffy-colored than those 

 of the herring gulls. In large colonies the nests were counted or sampled 

 and the proportion of adults of each species was extrapolated to derive an 

 estimate of the respective nesting populations. The low density of laugh- 

 ing gulls in the few colonies where they were found required no special 

 technique. 



Terns . The protective coloration of tern eggs and the lack of struc- 

 tured nests make tern nests difficult to find and count. A count or estimate 

 of adult birds is the best method for censusing large colonies. Correction 

 factors must be used to account for members of pairs away from nests and for 

 nonbreeders. In this inventory we assumed that 10 percent of the birds in 

 a colony were nonbreeders, based on previous work by Nisbet (1973). 



At sites containing several species the proportionate number of each 

 species must be estimated as well as the total number. An estimate of 

 each species population is then derived. 



Alcids . Common puffins and black guillemots nest in concealed sites 

 beneath large boulders or in rock crevices along the shoreline. Razorbills 

 nest on rock ledges or in crevices. Nest counts are extremely time consum- 

 ing and incomplete because nests are usually situated in inaccessible 

 locations. 



Methods used to census alcids are primarily for black guillemots since 

 few common puffins and razorbills nest on the Maine coast. To census 

 guillemots the shoreline of islands was circled very slowly by boat to flush 

 incubating birds from their nest sites. Counts of flushed birds were con- 

 sidered equivalent to a nest count. However, the resulting estimate is very 

 conservative since some incubating birds undoubtedly remain in burrows. In 

 some instances, counts of the total number of adults on the water adjacent 

 to an island were made after birds were flushed from nest sites. This number 

 was divided by two to give the number of breeding pairs in the colony, assum- 

 ing that there are few nonbreeding birds. Studies should be conducted to 

 evaluate the nonbreeding portion of alcid populations. Aerial counts are 

 not recommended for censusing alcids in Maine. 



NESTING CHRONOLOGY 



Information on nesting chronology is important to establish the best 

 time to conduct inventories and, if necessary, to make corrections for late 

 nesting birds. For this study most information was obtained through a 

 literature search. When possible, colonies were visited more than once 

 in 1976 and 1977 to provide additional information. 



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