Pigeon Guillemot (Cepphus columba) 



Pigeon Guillemots inhabit the nearshore 

 zone and are usually found along stretches of 

 rock coastline. They are most easily observed in 

 the early morning, before the egg laying season, 

 when both members of each pair frequent waters 

 adjacent to their colonies. 



Pigeon Guillemots usually nest in natural 

 rock crevices, talus, and boulder beaches (Thoresen 

 and Booth 1958, Drent 1965). They also use 

 burrows dug into loose conglomerate bluffs and 

 man-made structures, such as wharf timbers, drain 

 pipes, and within truck tires slipped on wharf 

 pilings (Campbell 1977, this study). In some 

 regions of California, Pigeon Guillemots and 

 introduced Rock Doves (Columba livia) may be 

 competing for nesting space. 



Pigeon Guillemots are some of the few alcids 

 to regularly lay two eggs (Bent 1946, Thoresen 

 and Booth 1958, Drent 1965). Eggs are laid on 

 bare rock, soil, or sometimes on a bed of pebbles 

 and shell fragments. Guillemots usually feed 

 close to shore and the proximity of the feeding 

 grounds to the colonies may help explain their 

 ability to sometimes raise two chicks. Pigeon 

 Guillemots, like all members of the family Alcidae, 

 dive for food using their wings for propulsion. In 

 California, fish are the principal food of guillemots 

 during the breeding season (Follett and Ainley 

 1976). This appears to be true throughout their 

 breeding range although near Kodiak, Alaska, 

 Pigeon Guillemots are known to eat small crabs 

 and shrimp (Krasnow et al. 1978). 



Following breeding, Pigeon Guillemots 

 largely disappear from the California coastline and 



do not reappear until just before the next year's 

 breeding season. Their wintering range is presently 

 unknown but we suspect that a northward move- 

 ment of birds takes place. 



CALIFORNIA COLONIES 



In California, Pigeon Guillemots breed from 

 the Oregon border south to Santa Barbara Island. 

 They are found breeding in large aggregations of 

 up to 3,000 birds, in smaller groups of only a few 

 birds, or as isolated pairs scattered along the coast 

 in suitable habitat. Delimiting colonies is often 

 difficult, especially in those regions where Pigeon 

 Guillemots are spread along the coast. In many 

 cases, colony boundaries have been based on 

 geographical landmarks and cover large sections 

 of coastline. 



The catalog total of Pigeon Guillemots in 

 California is about 12,000. We feel that this 

 number is conservative, although for any individual 

 nesting site our estimates may be either high or 

 low. Censusing Pigeon Guillemots is at best an 

 inexact science and is complicated by several 

 factors (see Materials and Methods). Although 

 many Pigeon Guillemot colonies were surveyed in 

 both 1979 and 1980, only the best of the estimates 

 for these two years are included in this catalog. 



The Farallon Islands (429 012), with 3,000 

 birds, have the largest population of Pigeon 

 Guillemots in California. The coastline between 

 Davenport and Point Santa Cruz (454 021) is 

 inhabited by about 1,300 guillemots. Other 

 locations with large numbers are Point Arguello 



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