Lesser in 1977 (unpublished) using a combination of line transects, quadrats, 

 and subjective evaluation of the burrow abundance and colony distribution. 

 Lesser suggested that petrel colonies be censused in early August when 

 active and inactive burrows can be distinguished. 



Double-crested cormorants . A ground count of nests is the best method 

 of censusing the nesting population. Counts of nests from aerial photographs 

 taken vertically above the colony are also an accurate means of censusing 

 cormorants. 



Wading birds . A nest count from fixed- or rotary-wing aircraft is the 

 best census technique for great blue herons in Maine since these birds nest 

 primarily in tops of trees. Verification of aerial counts by ground counts 

 also is recommended. Ground checks should be made early in the spring when 

 the adults are incubating and young are relatively immobile. Nest counts 

 from aerial photos are equally useful for censusing great blue herons. 



Black-crowned night herons were never observed from fixed-wing aircraft 

 and even when active nests were approached closely with a helicopter, the 

 adults were not seen. A nest count from the ground is considered the most 

 reliable method for censusing black-crowned night herons, snowy egrets, and 

 glossy ibises, since they nest lower in the trees than great blue herons. 



Common eider . Eider nesting islands are found readily by aerial surveys 

 in late April or May. If the surveys are timed accurately, counts of eiders 

 closely associated with islands can be used to provide a close approximation 

 of the nesting population. 



Nest counts in June provide a reliable estimate of the breeding popula- 

 tion. If nest counts are made, nests which are active and inactive (abandoned, 

 hatched, or destroyed by predators) should be tallied. Nest counts of eiders 

 can be disruptive because of predation by gulls. Eider eggs should be covered 

 with nest material after hens flush. 



Gulls . The three species of gulls nesting in the study area occupied 

 relatively small colonies. Aerial surveys were useful for locating the small 

 colonies and in many cases a reliable population estimate could be obtained 

 from a fixed-wing aircraft. Photographic counts may be a reliable way to 

 estimate gull populations early in the season when cover is not too dense. 

 The utility of this technique is being investigated. Almost all gull colonies 

 on the Maine coast were inventoried by boat. Total nest counts were made 

 whenever possible. If each nest in a colony could not be counted, a portion 

 of the nesting habitat was surveyed to provide a partial count of the relative 

 density of nests. An estimate of the breeding population was obtained by 

 extrapolating the partial nest count to the total area of the colony. This 

 technique frequently was used in conjunction with counts and estimates of 

 adult birds. Special attention had to be given whenever nonnesting subadult 

 birds, usually identifiable by plumage characteristics, were observed in the 

 colony. 



Herring and great black-backed gulls usually nested at sites containing 

 both species, but the nests often were distinguishable by the location of the 

 nest, size of the eggs, or color of the young. Black-backed gulls usually 



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