Seabirds of Alaska Maritime National Wildlife Refuge
Fork-tailed
Storm-Petrel (Oceanodroma furcata)
Leach’s Storm-Petrel (O.
leucorhoa)
These petrals are 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. Fork-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 the 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 here, 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 to 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.
