morning and afternoon. We tried to locate eggs 

 and chicks of Rhinoceros Auklets and Tufted 

 Puffins at several sites where we observed these 

 birds, but only at Prince Island (325 003) were we 

 successful. For the other sites in our study area, 

 we based our population estimates on the number 

 of birds in breeding plumage on or near the 

 colonies in 1979 or 1980. For some colonies that 

 had been previously intensively surveyed, we 

 relied on estimates in the literature. 



Pigeon Guillemots are some of the most 

 difficult of California seabirds to census. Finding 

 Pigeon Guillemot nests during brief surveys 

 of the rugged habitat where they usually nest is 

 nearly impossible. Also, numbers of birds around 

 a colony fluctuate greatly depending on the stage 

 of nesting and time of day. Distinguishing 

 breeders from non-breeders is impossible in most 

 cases, so our numbers reflect the total number of 

 guillemots at a colony rather than the number of 

 breeding birds. We found that Pigeon Guillemots 

 are present in large numbers around colonies in 

 the early morning but nearly disappear by mid to 

 late afternoon. Once incubation begins one 

 member of each pair is probably always absent 

 from view. The best time to census this species is 

 therefore in the early morning, before the egg 

 laying season, when both members of a breeding 

 pair are on the water near the colony. Nettleship 

 (1976) concluded that this is the best time to 

 census populations of the similar Black Guillemot 

 (Cepphus gryllc) in arctic and eastern Canada. 

 Surveying Pigeon Guillemots later in the day will 

 result in underestimation of numbers or even 

 failure to detect entire colonies. Most of our 

 surveys could not be conducted at this optimum 

 time, so guillemot estimates which appear in this 

 catalog are based not only on the numbers of 

 birds seen, but have been modified to reflect the 

 influences of time of day, stage of nesting, and 

 quality of habitat. These adjusted numbers, we 

 feel, provide the most realistic estimates of the 

 populations at each site, but they may be higher 

 or lower than actual guillemot numbers. Although 

 our population estimates are almost always many 

 times higher than those made during previous 

 surveys (1,285 percent higher for the entire 

 study area), we still feel they are conservative. 

 Differences in survey techniques and more com- 

 plete coverage of the coast are likely to account 

 for our higher numbers. 



Aerial surveys were our best means of 

 censusing Brandt's Cormorants and Common 

 Murres. In 1 979, we conducted nine aerial surveys 

 in order to cover the coast from Point Conception 



Jay Nelson and Bill Rodstrorn censusing cliff 

 nesting seabirds from a small boat at False Cape 

 Rocks (325 040). Photo by Art Sowls 



