Other less common migrants include the skua, parasitic jaeger, and pomarine 

 jaeger. They are offshore and pelagic species that only enter the 

 characterization area occasionally. 



Reproduction 



With the exception of the common loon all species of seabirds that breed along 

 the coast nest in colonies. Colonial nesting in birds is thought to evolve 

 when the following conditions prevail: (1) relative freedom from predation, 

 particularly ground predators, such as mammals and reptiles; (2) food sources 

 are concentrated and patchy in distribution, so that many individuals must 

 feed together and territorial defense of food supplies is not possible; and 

 (3) a shortage of preferred nesting sites exists, so that many individuals 

 must nest together. Colonial nesting in turn benefits individual pairs in 

 defending against predators. The major predators in seabird colonies are 

 other birds, primarily gulls, crows, and ravens. Colony members can sometimes 

 drive these predators away by attacking together. 



Nesting in colonies also helps birds locate food. Since food sources are 

 often widely distributed in marine systems, birds that are successful in 

 locating food are followed from the colony to the source by other birds. 



As a group, seabirds have small clutches (1 to 5 eggs), relatively protracted 

 development periods for nestlings, and delayed breeding in adults (up to 5 

 years for petrels). Low predation rates and patchy, often distant food 

 supplies, make it adaptive to invest more time and energy in a few eggs and 

 young rather than trying to raise a large brood (which might die of exposure 

 or starve). Even among the seabirds these reproductive characteristics vary. 

 Petrels lay one egg, nest in protected burrows, and delay breeding until the 

 adults are 5 years old. Petrels feed far offshore and spend much time 

 searching for food. They may remain away from the nest for up to 2 days. The 

 young develop very slowly to accommodate the scarce food supplies. They may 

 remain in the nest for over 60 days. 



In contrast, gulls, terns, eiders, cormorants, and guillemots lay two or more 

 eggs, usually in exposed nests, and breed at an earlier age (2 to 4 years). 

 The nesting islands are closer to inshore and estuarine waters, which are more 

 productive than offshore waters. Consequently the young develop more rapidly 

 than do petrels. 



Along the Maine coast, seabirds nest from mid-April (great black-backed gulls) 

 through late October (Leach's storm petrel). Each species has a peak laying 

 period that may vary up to three weeks, depending on weather conditions and 

 disturbances (figure 14-3). Also, birds in the southwestern regions (1 and 2) 

 begin nesting earlier than birds in the northeastern regions (5 and 6). The 

 laying peaks for several species overlap. Great black-backed gulls, herring 

 gulls, cormorants, and eiders start nesting in late April and early May, while 

 terns, alcids, Leach's storm petrel, and laughing gulls initiate nesting in 

 late May and early June. 



In late summer large rafts of moulting eiders form at several locations along 

 the coast. At the same time large concentrations of herring gulls and great 

 black-backed gulls occur in nearshore estuarine feeding and roosting areas. 

 These concentrations occur in August after the young birds have fledged. 



14-17 



10-80 



