estoration noteR book November 1998 Exxon Valdez Oil Spill Trustee Council Pigeon Guillemot Cepphus columba Photo courtesy USFWS By Katherine J. Kuletz (50%-80%) breed in Alaska. Surveys conducted by the U.S. U.S. Fish and Wildlife Service Fish and Wildlife since 1989 estimated the population of pi­ geon guillemots at 3,500 in Prince William Sound (PWS),2 Pigeon guillemots (Cepphus columba) are medium-sized 9,000 in lower Cook Inlet,3 [FIG.1] and 19,000 in southeast­ seabirds in the Family Alcidae, close cousins to auklets, murres, ern Alaska.4 murrelets, and puffins. The pigeon guillemot nests along rocky In PWS the guillemot population has declined by 67% since coastline from California to Alaska in the North Pacific and the 1970s.2 Detailed counts at study colonies confirm this along eastern shores of Siberia.1 Other members of the genus decline. Pre-spill counts of about 2,000 guillemots breeding at Cepphus are: black guillemots (C. grylle), which inhabit the the Naked Island complex in central PWS were twice as high North Atlantic and the Bering Sea coast of Alaska, and spec­ as post-spill counts.5 Although guillemots in PWS show clear tacled guillemots (C. carbo), in the Sea of Okhotsk and Ja- spill-related effects, the reason for the magnitude of the de­ pan.1 Pigeon guillemots, like all auks, forage by swimming cline is not well understood, and counts in 1985 suggest that underwater in pursuit of their prey. They nest mostly in small the decline began prior to the spill.5 Local threats to guillem­ scattered colonies or in solitary pairs. The estimated world ots include gillnet bycatch mortality, oil pollution, and preda­ population of pigeon guillemots is about 235,000 and most tion. Changes in marine ecosystems could affect food avail­ ability and regional population trends. Exxon Valdez Oil Spill Trustee Council 1 n o t eR bestoration o o k Annual Cycle and Nesting Habitat Although guillemot colonies may be limited Vital Statistics Little is known about the winter range of by nest sites in some locations, the adequacy of Population pigeon guillemots, but exposed coastlines ap­ local food supplies may be equally important, Approx. 3500 PWS; pear to be deserted in favor of more sheltered because guillemots forage within 7 km of their 9000 lower Cook Inlet inshore waters.1,6,7 Low numbers of guillem­ nests,7 and usually much closer.10,11,12,13 Population Trend ots remain in southcentral Alaska throughout the Nesting density probably varies due to the avail­ 6 67% decline in PWS since the winter. Guillemots begin to return to their ability of both suitable nest sites and food abun­ ‘70s, some areas show trend of breeding grounds in April, usually sporting their dance. Perhaps because they feed nearshore and continued decline since 1989 summer plumage. Breeding plumage is a star­ near their nests, guillemots can be found nest­ tling change from their winter plumage of mostly ing as isolated pairs or in small colonies scat­ Lifespan white head and belly and dark gray back. Adults tered along the coastline, although in a few lo­ 14+ years of breeding age are a sleek black, with white cations there are colonies of more than 1000 Adult Size wing patches and bright red feet that match the pairs.14 Length, 32-33 cm; wing span, red lining of the mouth. Younger birds have faint One or two eggs are laid in natural cavities, 175-188 cm; weight, 445-565 g. white streaking mixed with the black feathers. often in rock crevices in talus boulders or on In May, maximum numbers of birds are cliff faces or in labyrinth tree root systems. Some Breeding Season present at the colonies and courtship begins in birds nest in artificial structures. Occasionally Lay eggs May-June; earnest. The guillemots gather in groups on the a bird will construct a nest-scrape if soil, sand, fledging July-August water and on rocks near the colonies where they or gravel is present. The eggs are the size of Incubation/Fledging socialize and establish pair bonds. Compared chicken eggs and vary in color from white to Eggs hatch in 26-33 days; to other alcids, guillemots have the widest array slightly bluish or pale green, with variable gray chick fledges in 29-54 days. of vocal calls and behaviors to affect pair bond­ and brown blotches concentrated in a band at Clutch size ing and establish dominance hierarchies. Calls one end. Incubation is intermittent after the first One or two eggs per season; include various hunch-whistles, trills, and alarm egg is laid until the clutch is completed, usually 8,9 some replacement clutches screams to signal perceived dangers. Lively 3 days later, after which full-time incubation duet flights and chases over land and water, of­ begins.10 Both adults have a two-lobed brood Chick weights ten continuing underwater, can be observed dur- patch and share incubation of the eggs, exchang­ Hatch at 24-50 g, semiprecocial; ing this time. The distinctive red fledge at 350-550 g. legs and interior of the mouth may Maturity also play an important role in court­ Age at breeding approx. 3-4 yrs ship and social interactions. Pairs tend to be monogamous and gener­ Plumages ally retain the same mate and de­ Winter and juvenile, gray above / fend the same nest site in succes­ white below; breeding, blackish- sive years.1,10 brown iridescent with white wing Pigeon guillemots are found patch along rocky coastlines during the Diet breeding season, which in Gunnels, pricklebacks, ronquils, southcentral Alaska is May through sculpins, flatfish, rockfish, small August. Guillemots are flexible in crustacea, squid, sand lance, nest selection and will use isolated smelt, juveniles of cod, herring, offshore islands or onshore sites. pollock, and salmon Nest predation by birds and mam­ mals can be intense, so nest site se­ lection is vital to a pair’s breeding Photo by Greg Golet success. River otter and mink prey on adults, eggs and chicks while A guillemot chick at 6-8 weeks is ready to leave the nest. ravens, crows, jays and magpies take unattended eggs or chicks if they can reach ing incubation duties approximately every 4-8 them. Nests can be found by the smell and pres­ hours. ence of chick feces on the rocky cliffs. The high- Chicks hatch after an average of about 32 pitched peeping of chicks begging for food, or days, with the first-laid egg usually hatching 1­ the adult delivering fish to their young, also help 2 days before the second.7,15,16 The size ad­ predators (and researchers) to locate nests. vantage of the ‘alpha’ chick can become critical 2 Exxon Valdez Oil Spill Trustee Council Rn estorationo t e b o o k if food is scarce, resulting in many single-chick Pigeon Guillemot Study Sites broods later in the season. The chicks are semi- precocial and able to stand after only a few hours. Because the chicks cannot thermoregulate for the first few days, they are brooded by adults during this period. At hatching the chicks are covered by a thick black-brown down that later Naked Island becomes gray. Feathers begin to appear about Colonies day 12 and chicks are fully feathered by day 20­ 25, although tufts of down persist. Juvenile Jackpot Island plumage after fledging is similar to adult winter Colony Prince plumage, but with more gray on the head, throat, William and belly. Sound Chicks are fed by both parents, each carrying one fish or invertebrate at a time in their bill back to the nest throughout daylight hours. Chicks eat the fish whole, head-first, and gain Kachemak Bay Colonies weight rapidly, tripling their mass within 10 days.10,17 After this rapid start, growth rates can vary greatly between chicks, and fledging age may range from 29 to 54 days.1 Sometimes FIG. 1. Colonies of pigeon chicks exceed adult weights, but lose some herring, smelt, and gadids are also significant 11,20,21 guillemots can be found weight just prior to fledging. Fledglings usu­ prey species. [FIG.2]. Individual throughout the oil spill ally depart from the nest at night or early in the guillemots, however, often show distinct diet region. Monitoring of evening. The young, which are independent preferences, even in the presence of apparently colonies has taken place in abundant alternative prey species.10,11,12,22 Kachemak Bay and in from their parents, are capable swimmers and Prince William Sound at divers, but do not fly for several weeks. For example, some birds would catch and feed Jackpot Island and at Guillemot pairs, even within the same colony, their chicks only blennies, while others at the Naked Island. Naked Island exhibit a wide range in breeding phenology. In same colony would use sand lance or Pacific has five distinct colonies included in the study. Alaska, fledging occurs from July to September. herring. In Kachemak Bay, diet appeared to vary Most guillemots in southcentral Alaska fledge with location of the colony, suggesting that prey from late July to mid August, with the peak oc­ use was a function of local habitat (Litzhow and curring during the first two weeks in August.6,11 Piatt, unpubl data). At Naked Island, however, The numbers of adult guillemots at the colonies there were no significant differences in the diet gradually decrease as the chicks fledge. preferences among colonies.22 Little is known about the movement of im­ Because different fish are not equal in nutri­ mature birds in the fall, but estimated chick sur­ tional value, the feeding preferences of adults vival is around 40%.