Cassin's Auklet (Ptychoramphus aleuticus) 



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World Breeding Range 



The Cassin's Auklet is one of the most 

 widespread members of the family Alcidae in the 

 North Pacific. Cassin's Auklets build their nests 

 in burrows on offshore islands that have a sufficient 

 mantle of soil. These tiny alcids are nocturnal at 

 their breeding colonies and are likely the most 

 pelagic of all the California alcids (Hunt et al. 

 1979). A population is present on the Farallon 

 Islands (429 1 2) all year, but wintering northcoast 

 birds are found between 10 and 50 miles offshore 

 (Manuwal 1974a, Yocom and Harris 1975). 



Throughout their range Cassin's Auklets 

 usually nest in burrows, but on the Farallon 

 Islands birds also may use rock crevices, debris 

 piles, cracks under buildings, and large caves 

 (Thoresen 1964). Each female lays a single 

 creamy white egg, but may lay a second egg if the 

 first egg is destroyed (Manuwal 1974a). Adult 

 Cassin's Auklets develop two incubation patches 

 on the body, one beneath each wing (Manuwal 

 1974b). These incubation patches are found only 

 among several species of alcids, including Xantus' 

 Murrelets, Rhinoceros Auklets, and Tufted Puffins. 

 Breeding Cassin's Auklets also develop a gular 

 pouch, used to store food for young that are fed 

 by regurgitation at night (Speich and Manuwal 

 1974). Small fish and pelagic crustaceans form 

 the mainstay of the diet of Cassin's Auklets 

 (Manuwal 1974a, Hunt et aL 1979). 



CALIFORNIA COLONIES 



Cassin's Auklets breed in California from the 

 Channel Islands to Castle Rock (325 006). Of the 

 know colonies in California the Farallon Islands 

 colony is by far the largest, containing 105,000 

 auklets. Of the 23,000 Cassin's Auklets nesting in 

 the Channel Islands, 20,000 are found on Prince 

 Island (501 004). Castle Rock, near the Oregon 

 border, has an estimated population of 3,600 

 birds. 



Cassin's Auklets are difficult to census 

 because of their nocturnal lifestyle, burrow 

 nesting habits, and highly pelagic nature. We 

 found no new colonies during our surveys and 

 have made no new population estimates for this 

 species. 



HISTORICAL STATUS 



Surprisingly, Cassin's Auklets were rare on 

 the Farallon Islands in the mid-1 800's. Ainley 

 and Lewis (1974) relate this scarcity to a period 

 of more than two decades when warm, tropical 

 water moved north along the California coast. 

 They hypothesize that populations of Cassin's 

 Auklets increased when cold water returned to 

 the region. Now Cassin's Auklets are the most 

 abundant birds on the Farallon Islands. 



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