- The study, the species and the locale

Discovery of a colony and the beginning of a long-term study

George Divoky's discovery of a Black Guillemot colony on a northern Alaskan barrier island in 1972 began an ongoing study of a high arctic seabird at one of the most remote locations in North America. The island, surrounded by pack ice and covered by snow for much of the year, is home to a unique colony of seabirds with all nests in boxes and other manmade structures allowing detailed monitoring of each nest.

George first visited the island in 1972 and discovered that Black Guillemots were using boxes and other debris from a 1950s military camp as nesting cavities for raising their young. Guillemots typically nest in natural cavities, usually associated with coastal cliffs and rocky shorelines. In northern Alaska however, the low coastal tundra bluffs and gravel beaches lack any fissures or spaces suitable for breeding. George's discovery of the Cooper Island colony provided the first breeding record for guillemots in the Alaskan Beaufort Sea.

In 1975, George returned to Cooper Island and found that some of the cavities he created in 1972 were now being used as nest sites and the colony had increased to 18 pairs. From 1975 through the mid-1980s George created nest sites and by 1989 the colony had increased to over 200 pairs and had become the largest Black Guillemot colony in Alaska. George has monitored the size, breeding chronology, and breeding success of the colony from 1975 to present, making it one of the longest ongoing studies of a seabird in the world. While the initial motivation in maintaining the database was to examine the demographics of a relatively long-lived bird, in the mid-1990s it became clear that there were long-term changes in breeding biology and population size that might be related to environmental changes occurring in the Western Arctic.

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A seabird generalist at home in the arctic

The Black Guillemot has a number of life history characteristics that make it an ideal monitor of changes in the marine environment in general and the Arctic in particular. Guillemots, of which there are three species, belong to the seabird family known as auks, or alcids. The most abundant seabird family in the Northern Hemisphere, the alcid family includes murres, puffins, auklets and murrelets. All members of the family dive to obtain prey below the sea surface typically in offshore pelagic waters some distance from land. Guillemots, however, are frequently associated with nearshore waters for most of the year, where they feed on prey both in the water column and in shallow benthic (bottom) habitats. While a number of alcid species, such as puffins and auklets, have specialized bills for obtaining a specific prey type, guillemots have a generalized bill that it uses to feed on both fish and invertebrates, although parents feed nestlings fish almost exclusively. Guillemots are also generalists in their choice of the nest sites, where they incubate eggs and raise their young. Any covered space deep enough to hide the nest contents or attending adult can allow successful breeding. Shoreline cavities are most commonly found on rocky shorelines or headlands, where guillemots are most abundant, but nesting regularly occurs in other natural cavities, such as driftwood piles and increasingly in manmade structures, such as docks and seawalls.

Guillemots are also far less colonial than most seabirds with single breeding pairs not uncommon. The ability to breed successfully as single pairs combined with their plasticity in nest-site selection allows guillemots to occupy areas and exploit nesting opportunities that highly colonial species with more restricted nest site requirements cannot. These characteristics allow it to be the most widely distributed seabird species in the Arctic Basin.

It is what guillemots do after breeding, however, that makes them an ideal monitor of arctic marine ecosystems. While every summer the region is home to millions of seabirds, waterfowl and shorebirds, with few exceptions all undertake major migrations at the end of the breeding season and spend the next nine months in more southern latitudes. In contrast, Black Guillemots in the western Arctic undertake limited migrations, wintering no further south than the pack ice in the central Bering Sea and apparently as far north as open water is present. There are regular winter observations from Point Barrow, where cracks and open water are maintained throughout the frigid winter by the movement of ice by winds and currents, and where guillemots are apparently unfazed by the extended darkness as the sun remains below the horizon for three months. The ability of Black Guillemots to exploit arctic habitats throughout the year means that variation in their demographics, breeding biology or composition of their tissues reflects conditions in the Arctic. Those bird species that visit the region only to breed could be expected to have influences from more southern latitudes.

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A nearshore environment dominated by ice and snow

Our study colony on Cooper Island, a low sand and gravel bar, is 25 miles east of Point Barrow, the furthest north point in Alaska. Snow and ice dominate the landscape of the northern Alaska coast for much of the year. Snow can fall on any day during the short arctic summer but air temperatures just above freezing from June to August melt the winter snow and prevent any accumulation until September. During this snow-free period the island and adjacent coastal tundra are home to seabirds, shorebirds and waterfowl that raise their young utilizing the 24-hours of sunlight and large invertebrate and fish populations of the arctic.

While Guillemots are in the region of Point Barrow in numbers as early as March, they return to Cooper Island only when the snow melts in early June and entrances to nest cavities become snow-free. Initiating breeding as soon as the snow melts is important to Black Guillemots, whose 80-day long breeding period is extremely long for an arctic bird, especially in an area where the annual snow-free period has only recently begun to exceed 80 days. Even in recent years, late summer snow has blocked nest-site entrances in late August preventing parents from delivering fish to their young.

While guillemots encounter snow at the start and end of their breeding period, sea ice is typically part of their marine existence for the entire year. Sea ice has a range of effects on the physical and biological structure of marine waters. The most important to seabirds is the barrier it creates between birds and potential prey in the water. However, because ice cover is rarely complete, diving species like the Black Guillemot can exploit cracks and other openings in the ice to access the waters beneath the ice. Most importantly perhaps, the underside of arctic sea ice supports a community of fish and zooplankton that live on phytoplankton and algae blooms that occur within and on the undersurface of ice. This under-ice fauna provides a prey source associated with a substrate that is similar to the nearshore benthic communities that guillemots rely on elsewhere.

The guillemots close association with snow and ice habitats makes it a sensitive indicator to atmospheric warming. Species that have a major part of their life history constrained by or benefiting from the presence of ice or snow should be among the first to show the effect of warming in the Arctic. Snow and ice habitats, especially those that are near freezing for part of the year can respond immediately to changes in air temperature.

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