CASSIN’S AUKLET Ptychoramphus aleuticus Original1 prepared by Anne Harfenist Species Information The upper parts are dark grey and the underparts are dark grey shading to paler grey with a white Taxonomy belly. There is a white crescent above and below each eye; the upper crescent is more prominent. The The Cassin’s Auklet is a member of the family Alcidae, short pointed bill is black; legs and feet are blue. Iris the auks, and is the only species in the genus colour changes with age: chicks have a brown iris Ptychoramphus. According to mitochondrial DNA which gradually change to the silver-white colour evidence, it is most closely related to the other genera found in adults; the irides of intermediate-aged of Pacific planktivorous auklets, Aethia and birds are usually a combination of brown and silver Cyclorrhynchus (Friesen et al. 1996). There are two (Manuwal 1978). subspecies of Cassin’s Auklet: Ptychoramphus Juveniles are generally paler than adults and have a aleuticus aleuticus and P. aleuticus australe (Manuwal white throat. Nestlings are covered with grey down and Thoresen 1993). P. aleuticus aleuticus is found over most of the body with white down on the belly over most of the species’ range from Alaska to until they develop feathers. Guadalupe Island in Baja California; P. aleuticus australe is the more southern form. Distribution Description The Cassin’s Auklet spends almost its entire life on the ocean, coming to land only to breed through The two subspecies are almost identical in appear- most of its range. ance although the more southerly birds are smaller in length and mass (Manuwal and Thoresen 1993). Global For the aleuticus subspecies, adult length is ~23 cm, The breeding range of the Cassin’s Auklet extends wing length is about 125 mm (Nelson 1981), and from the middle of Baja California north along the adult mass is 150–200 g (Manuwal and Thoresen west coast of North America to southeast Alaska and 1993). There is a significant clinal increase in body along the south coast of the Alaska Peninsula west size from Baja California through California along the Aleutian Islands (Manuwal and Thoresen (Manuwal and Thoresen 1993); birds from British 1993; Gaston and Jones 1998). No Cassin’s Auklet Columbia and Alaska are similar to California birds colonies have been reported from Kodiak Island to (Gaston and Jones 1998). Within British Columbia, Prince William Sound in the Gulf of Alaska despite birds breeding on Frederick Island have a longer the availability of suitable nesting habitat (Manuwal mean tarsus length than those breeding on Triangle and Thoresen 1993; Gaston and Jones 1998). The Island. However, too few data exist to determine at-sea distribution of the birds during the breeding whether other measurements of the Frederick Island season covers approximately the same geographic birds are also larger (A. Harfenist, unpubl. data). range. The Cassin’s Auklet is a small grey seabird with The winter range of the Cassin’s Auklet extends short, broad rounded wings and chunky body shape farther offshore into deeper oceanic waters than (Manuwal and Thoresen 1993; Gaston and Jones 1998). Males and females are similar in appearance and the plumage does not change during the year. 1 Volume 1 account prepared by A. Derocher. 1 Accounts and Measures for Managing Identified Wildlife – Accounts V. 2004 1 2 Accounts and Measures for Managing Identified Wildlife – Accounts V. 2004 does the summer range (Gaston and Jones 1998). In the outer vegetation edge (Campbell et al. 1990; addition, the birds winter along the entire western Rodway and Lemon 1991a); on Triangle Island, coast of the Baja Peninsula. They do not seem to burrows extend several hundred metres inland winter in southeast Alaska. (Rodway et al. 1990b). British Columbia Life History The Cassin’s Auklet breeds at 61 colonies on offshore Diet and foraging behaviour islands along the western and northern coasts of Vancouver Island, the northern mainland coast and Cassin’s Auklets are planktivores that feed mainly on the Queen Charlotte Islands/Haida Gwaii (Rodway macrozooplankton (primarily copepods and et al. 1988, 1990a, 1990b, 1994; Rodway and Lemon euphausiids) and larval fish (e.g., Vermeer et al. 1985; 1990, 1991a, 1991b). The largest breeding colony in Manuwal and Thoresen 1993; Hedd et al. 2002). The the world is at Triangle Island in the Scott Island diet of Cassin’s Auklets varies across its range and group off northwestern Vancouver Island (Manuwal significant interannual variation has been observed and Thoresen 1993). The marine distribution at some sites (Manuwal and Thoresen 1993; Gaston includes the entire B.C. Coast during the breeding and Jones 1998). Diet studies carried out on Triangle season and all but perhaps the waters around the and Frederick islands in 1994–1998 found that northwestern side of the Queen Charlotte Islands/ copepods (mainly Neocalanus cristatus), euphausiids Haida Gwaii archipelago in the winter (Campbell (primarily Euphausiia pacifica, Thysanoessa spinifera, et al. 1990; Gaston and Jones 1998). There are no T. inspinata) and larval fish (including Sebastes spp., records from the Interior of British Columbia Ammodytes spp.) comprised 90–99% of the diets by (Gaston and Jones 1998). mass (Hedd et al. 2002; A. Harfenist, unpubl. data). Other items in the diet included amphipods, Forest region and districts brachyurans, and carideans. The relative importance Coast: Campbell River, North Coast, North Island, of each prey type varied between years, but the diet Queen Charlotte Islands, South Island of birds on Frederick Island included higher percentages of copepods and euphausiids and a Ecoprovinces and ecosections lower percentage of fish than that of auklets nesting Nesting: on Triangle Island. Chick growth was depressed on COM: HEL, NCF, NWL, QCT, SKP, WIM, WQC Triangle Island when copepods were replaced in the diet by larval rockfish (Hedd et al. 2002). At three At-sea: colonies in the Queen Charlotte Islands/Haida Gwaii COM: DIE, HES, JOS, NCF, QCS, QCT, VIS in the 1980s, copepods (N. cristatus), and GED: JDF, SOG euphausiids (T. pinifera, T. longipes) dominated the NOP: SAP, TRP diet (Vermeer et al. 1985). Biogeoclimatic units (nesting) Almost all of the information about diet of the CWH: vh1, vh2, vm1, wh1 Cassin’s Auklet is from studies of the food that adults bring back to their nestlings at the colony; the Broad ecosystem units overlap between the diet of nestlings and that of CH, HS adults and non-breeding birds is unknown. Chick meal sizes averaged 26–27 g over 2 years on Distance to ocean Triangle Island. Throughout their range, most burrows are within Cassin’s Auklets forage solely in marine waters, 500 m of the ocean (Gaston and Jones 1998). On the usually in areas of cold upwellings near the conti- Queen Charlotte Islands/Haida Gwaii and northern nental shelf break or over seamounts (Vermeer et al. mainland coast, most burrows are within 30 m of 1985; Manuwal and Thoresen 1993). Birds nesting 3 Accounts and Measures for Managing Identified Wildlife – Accounts V. 2004 3 on Triangle Island foraged 30–90 km from their Island (3.5–5.4 g/day) was lower than that at Frederick colony in waters >1500 m deep (Boyd et al. 2002). Island (5.0–5.7 g/day) over 5 years of study (Hedd et al. Their foraging behaviour is described as pursuit 2002; A. Harfenist, unpubl. data). Nestling growth was diving and they use their wings to propel them reduced during an El Niño year on Triangle Island, under water as they dive to depths of 20–80 m but not on Frederick Island (Bertram et al. 1999). The (Burger and Powell 1990). Cassin’s Auklets usually nestling period averages ~45 days in British Columbia feed in small groups but occasionally forage in large (Gaston and Jones 1998). In most years, chicks fledge flocks (Manuwal and Thoresen 1993). They feed at an average mass of 162–175 g in British Columbia during both day and night (Manuwal and Thoresen (Vermeer and Lemon 1986; Vermeer et al. 1997; 1993). During the breeding season, adults transport Gaston and Jones 1998; Hedd et al. 2002). However, in captured prey back to their chicks in a specialized a poor growth year, fledging mass averaged 126 g on throat pouch. Triangle Island. Chicks depart from the colonies at night unaccompanied by their parents. Reproduction Productivity is between 0.5 and 0.7 fledged chicks Cassin’s Auklets nest in burrows at colonies of up to per breeding pair per year at most colonies in most over 500 000 pairs (Manuwal and Thoresen 1993). years (Gaston and Jones 1998). Hatching success is The timing of reproduction varies across the species’ difficult to measure because disturbance during range: in British Columbia peak laying is from late incubation can cause desertion. Thus, the 70% March–late April, peak hatching from late April–late hatching success figure given for Frederick Island May and peak fledging from early June–early July (Vermeer and Lemon 1986) is probably low. (Gaston and Jones 1998). Timing is delayed in warm Fledging success (chicks fledged/egg hatched) was water El Niño years (Bertram et al. 1999). In the 89–99% on Frederick Island (Vermeer and Lemon Queen Charlotte Islands/Haida Gwaii, birds nesting 1986; Vermeer et al. 1997; A. Harfenist, unpubl. off the southeast coast tend to breed about 2 weeks data) and 47–93% on Triangle Island (Hedd et al. earlier than those nesting off the northwest coast 2002). Annual variation in reproductive success is (Vermeer et al. 1997). Breeding is earlier and more related to availability of prey which is, in turn, extended in the southern part of the birds’ range: in related to oceanographic conditions (Manuwal Baja California breeding begins in late November 1979; Ainley and Boekelheide 1990; Bertram et al.