|
| |
Passage Canal
Gulls
|
![[Gulls]](gull.gif) Three large gulls are commonly found in Alaska. These are the glaucous-winged
gull (Larus glaucescens), glaucous gull (L. hyperboreus),
and herring gull (L. argentatus), in order of decreasing abundance.
These gulls are closely related, and hybrids are not uncommon. |
Glaucous-winged Gulls
|
Glaucous-winged gulls are the common “seagulls” familiar to many on the
south coast
of Alaska. Glaucous-winged gulls breed in Alaska from the British Columbia
border to the end of the Aleutian chain and northward to Bristol Bay, western
Nunivak Island, and the Pribilofs. |
|
General description: Adults have white heads and bodies, pink legs,
brown eyes, gray backs, and wing tips typically the same shade of gray as the
back. Their heads are heavily flecked with gray in winter. Recently fledged
juveniles are dark-brownish gray. The plumage becomes lighter each year to age
4, when adult coloration is acquired and they first begin breeding. Adults
typically live about 10 years and average 23 to 26 inches (58-66 cm) in length. |
|
|
|
|
Life history: Glaucous-winged gulls are found principally in
intertidal coastal habitats, although they follow major rivers and salmon
streams inland. They also range hundreds of kilometers seaward, especially in
winter. These birds are adaptable to a wide variety of natural and artificial
settings, including highly urbanized environments. Efficient garbage collectors,
they congregate at natural food sources such as salmon streams where they
perform a useful function—they scavenge intertidal areas, riverbanks, and open
sea for dead fish, invertebrates, birds, and mammals. These gulls also take
small live fish at sea and in intertidal pools and prey upon eggs and chicks of
other birds. They feed in circling flocks over fish schools and floating waste.
Unfortunately, gulls tend to flock around onshore fish processing plants,
garbage dumps, sewage outfalls, offshore factory ships, and trawlers. Thus their
populations increase rapidly when new sources of food become available, and
artificially high populations cause many problems. Glaucous-winged gulls were
demonstrated to be vectors of Salmonella in an epidemic associated with
contaminated water supplies at Ketchikan. In some places, glaucous-winged gulls
also pose a hazard to aircraft, especially where garbage dumps are close to
airports. Unless care is taken to reduce the availability of artificial food
supplies, industrial and economic development of Alaska will cause gull
population explosions with the resulting problems for public health, safety, and
conservation of other Alaska seabirds. |
|
Gulls tend to colonize and are very aggressive, often exhibiting much
antagonism toward members of their own and other species. In late winter and
early spring, glaucous-winged gulls appear at their colony sites, often before
the snow melts. They prefer open, grassy hillsides of islands but will nest in a
variety of locations. Colony size may range from less than 10 to as many as
10,000 pairs. A clutch of one to three eggs is laid in mid- to late May. Chicks
hatch in mid- to late June and are raised within the nesting territory. |
|
Glaucous-winged gulls are partially migratory; some populations shift to
British Columbia, Washington, Oregon, and California in fall and winter. The
Southeast Alaska, Vancouver, B.C.–Puget Sound area is a major wintering area
for glaucous-winged gulls. Others remain in Alaska throughout the year. |
|
Glaucous-winged gulls have few natural enemies; ravens, crows, and jaegers
take eggs; bald eagles take chicks, juveniles, and adults. However, most loss is
because of cannibalism and territorial defense killings by other gulls.
|
Glaucous Gulls
|
Glaucous gulls breed along the coast of western and northern Alaska from the
Yukon-Kuskokwim Delta to Demarcation Point on the Canada border and on several
islands in the Bering Sea. The center of abundance of glaucous gulls in Alaska
is the Yukon-Kuskokwim Delta and the east side of the Bering Strait. The largest
breeding concentration of glaucous gulls is on St. Matthew/Hall Island. Glaucous
gulls are common in the Aleutians in winter. |
|
General description: Glaucous gulls are somewhat larger than
glaucous-winged gulls, have white bodies and heads, yellow eyes, gray backs, and
white wing tips. Adults average 25 to 31 inches (58-79 cm) in length. Glaucous
gulls first breed at age 4. Immature glaucous gulls are light grayish-brown in
their first year and nearly all-white (except for black-tipped bills) in their
second year.
|
|
Life history: Glaucous gulls are occasionally seen in spring and
summer along the south coast of Alaska as far as Cordova, Yakutat, and Glacier
Bay. They occur on river deltas, coastal tundra, lagoons, sea cliffs, barrier
islands, and pack ice. They are scavengers as well as important predators on
waterfowl and other seabirds. However, coastal glaucous gulls away from marine
bird colonies feed mainly on fish. Glaucous gulls nest in colonies on sea cliffs
as well as in isolated pairs on tundra ponds. Colony size is usually far smaller
than that of glaucous-winged gulls. Glaucous gulls appear on nesting territories
before snow melts. They begin breeding in May. Clutch size is usually three eggs.
Newly fledged juveniles remain with their parents close to nesting territories
for several weeks after learning to fly, gradually moving to the sea in
September and October. |
|
Surveys of 1,500 miles (2,400 km) of northwestern Alaskan coast suggest that
glaucous gulls may be entering a period of rapid population growth. Domestic and
industrial development activities on the North Slope are generating large
volumes of solid waste in unnatural settings, precisely the sort of environment
that facilitates explosive increases in juvenile gull survival. Artificially
high glaucous gull populations will pose problems in northern and western Alaska
similar to the problems abnormally high glaucous-winged gull populations present
in southcoastal areas. |
Herring Gulls
|
Herring gulls have white heads and bodies, gray backs, typically yellow eyes,
and black wing tips with small white spots. Total length is 22 to 25 inches
(56-64 cm). Juvenile herring gulls are difficult to tell from juvenile
glaucous-winged gulls. Herring gulls are usually found breeding in low numbers
on boreal lakes and rivers in interior Alaska. Some herring gulls, however,
breed on the south coast of Alaska, notably in Upper Cook Inlet near the mouth
of the Susitna River; at Dry Bay, mouth of the Alsek River, near Yakutat; and in
Glacier Bay in recently deglaciated fjords. Hybridization with glaucous-winged
gulls occurs in these locations. Hybrid gulls display characteristics of both
these parental forms and are found at river mouths and near tidewater glaciers.
They nest on flat gravel bars, sloping grassy hillsides, and on nearly vertical
cliff faces. A Siberian form of the herring gull (Larus argentatus vegae)
breeds on sea cliffs on St. Lawrence Island and occasionally appears in western
Alaska, where it hybridizes with glaucous gulls. In addition, many glaucous
gulls on the Yukon-Kuskokwim Delta show signs of interbreeding with
glaucous-winged gulls.
|
|
Almost all features of reproductive biology of Interior herring gulls
resemble those of glaucous-winged gulls. However, the food of Interior herring
gulls is limited and consists mainly of fish. This may account for their lower
numbers. Alaska herring gulls are completely migratory, leaving lakes and rivers
for the coast in September. Herring gulls banded on Alaska lakes have been
resighted during winter in southern California and Mexico. Herring gulls return
to Alaska lakes in May. |
|
Alaska's herring gull populations are not likely to expand in the foreseeable
future because of restricted nesting space and lack of substantial sources of
artificial food. Indeed, as recreational boating traffic on lakes increases,
disturbance of their relatively small colonies may result in population declines.
|
| |
|
