COLONY CENSUS 



Standardization of census methods is desirable. The determination of the 

 appropriate census technique depends upon the particular species and number 

 of species to be inventoried, the size of the population, the size and geo- 

 graphic location of the colony site, and the nest substrate. These factors 

 are compounded by the accessibility of the colony, the breeding chronology, 

 and the availability of manpower. The methods described herein were used to 

 census waterbirds in the Maine study area. These techniques may not be 

 applicable in all situations. The judgement, intuition, and experience of the 

 observers must be relied upon for choice of the most appropriate survey 

 method. 



Nesting islands were visited by boat starting the last week in May to 

 determine the number of nesting pairs for each species. Nest counts were 

 made where possible. Two teams of three observers censused the same part 

 of the coastal region in both 1976 and 1977. In both years two of the three 

 members of each crew were the same, so that in the second year of the study 

 each team was better prepared to inventory effectively. 



In Maine, identification of colonial waterbirds presented few problems. 

 The common, Arctic, and roseate terns occasionally nested in mixed colonies 

 and spedal attention had to be given to determine the species composition of 

 those colonies. Since all of the Maine seabird colonies except two were on 

 coastal islands, the physical size of the island often demarked the size of the 

 colony as well. Most of the seabird colonies were located on relatively small 

 islands or limited to parts of larger islands. 



Estimates of Nesting Populations from Aenal Photographs 



On 14-16 June 1977, low-level photographs of all colonies within the 

 study area were made with a K-17 aerial camera (9" x 9" format) mounted on 

 a U.S. Fish and Wildlife airplane. Counts of nesting double-crested 

 cormorants, gulls, and great blue herons were made from the aerial 

 photographs in a few cases. The negatives of the aerial photographs are 

 filed at the Maine Cooperative Wildlife Research Unit with an index. Figures 

 2 and 3 are examples of these photographs. 



Census Method for Each Species 



Leach's storm-petrel . Adult petrels never were seen in the vicinity of 

 colonies during daylight hours, therefore finding colony sites was difficult. 

 The only method used in this inventory was to ground check all islands in 

 the offshore area. Petrels were found nesting on wooded islands and treeless 

 islands, islands with rocky soils, and those with deep organic soils. Identifi- 

 cation of nesting burrows was the only positive indication that an active 

 colony was on an island. Remains of dead birds sometimes provided a clue to 

 the location of colonies. 



A count of active burrows is the most reliable method for estimating a 

 petrel population. However, because burrows are difficult to locate, these 

 counts provide a low population estimate in most cases. The large colonies of 

 Leach's storm-petrels on Little Duck and Great Duck islands were censused by 



6 



