Seabirds
of Alaska Maritime National Wildlife Refuge
Fork-tailed Storm-Petrel
(Oceanodroma furcata)
Leach's Storm-Petrel (O. leucorhoa)
Among
the smallest and most delicate of birds that spend much of their life on the open
ocean.
RANGE
Both are found throughout the North Pacific and
in Alaska from the western Aleutians through the Gulf of Alaska and commonly nest
in mixed colonies. Fort-tailed storm-petrels also nest in the Kuril Islands
and south to northern California.
Leach's storm-petrels have a wider range,
breeding southwest to northern Japan and southeast to Baja California. They range
widely in winter, becoming common in the waters of the central Pacific. In the
Atlantic, colonies are known from northeast United States to Labrador, Iceland,
the Faroes, and the British Isles.
PLUMAGE
The pale gray feathering
of the fork-tailed is unique among typically dark storm-petrels.
NOCTURNAL
HABITS
Storm-petrels are strictly nocturnal on their nesting colonies,
always arriving at their nest site before dawn and leaving after dark This minimizes
encounters with gulls and other avian predators that hunt in the daylight.
NESTING
Storm-petrels
nest underground, out of sight of avian predators. Fork-tailed storm-petrels
usually nest in crevices between talus or in rocky soil. The Leach's dig
burrows in soft grassy soil. Each can use the other's nesting habitat to some
extent.
EGG
Single. Incubation duties are shared in shifts
of several days, allowing the adults to forage over a vast area, even during nesting.
FEEDING
RANGE
They find their food far from their breeding colonies. The fork-tailed
storm-petrel feeds over the outer continental shelf and adjacent deep ocean.
Leach's typically feed only over the deep ocean.
FOOD
Storm-petrels
seize various zooplankton, small fish, and squid as they sit or patter over the
surface of the water. Zooplankton or squid are common in their diets, but in some
parts of the Gulf of Alaska and Bering Sea, the birds may depend on fishes such
as capelin and sandlance.
DANGERS ON LAND
Storm-petrels are
highly vulnerable to non-native, introduced predators such as foxes, rats, and
other rodents that can easily dig out or enter their underground nest burrows.
Islands where foxes were introduced lost their storm-petrel colonies. The birds
have successfully returned to nest after the alien foxes died out or were removed.
Storm-petrels
are also vulnerable to human visitors walking over their nesting burrows and crushing
them or dogs digging them out. Introduced cattle also trample and collapse the
fragile burrows, causing desertion even of nearby burrows that escape destruction.
DANGERS AT SEA
At sea at night, storm-petrels are frequently
attracted to lights on ships and occasionally alight on the decks where they are
easily captured.
POPULATION ESTIMATES
Storm-petrels require
intensive work to count accurately because of their underground nests and nocturnal
movements. Estimates range up to 6 million for each species in the state or about
one fifth of all seabirds in Alaska. Single colonies number in the hundreds of
thousands.
