Bird of the Month: Fork-tailed Storm Petrel
By Andy McCormick
Andy McCormick, Volunteer and Former Board President of Eastside Audubon
One of the most common pelagic birds of the North Pacific Ocean the Fork-tailed Storm Petrel is seldom seen from shore. It spends eight months of the year at sea. It flies close to the surface of the ocean with short wing beats and will often sit on the water and forage in small groups. It is almost never seen in large flocks. It forages on deep, cold water around the continental shelf where it will pick up small fish, plankton and surface oils while skimming the surface of the ocean.
You can see a video of the fluttering, zigzagging flight of the Fork-tailed Storm Petrel at You Tube . The two-minute video also allows for size comparisons with other species including gulls, shearwaters and an albatross.
A SILVERY, FAIRLY-LIKE BIRD
Fork-tailed storm petrel
Scientific Name: Oceanodroma furcata
Length: 8.75”
Wingspan: 19”
Weight: 2.1 oz (60 g)
AOU Alpha Code: FTSP
Unique among Northern Hemisphere storm petrels, the Fork-tailed is a silvery gray color. All others in the north are dark brown or black. It has a dark carpal bar giving the bird a distinctive M-pattern across its wings when in flight (Alderfer). The head is gray with a dark mark through the eye. The under wing coverts are dark. The Fork-tailed is silent on the sea, but has a weak raspy call on the breeding grounds.
Oceanodroma, ocean runner, from Greek okeanos, ocean, and dromos, running, is an appropriate name for the genus of storm petrels, which, when flying with their feet extended often touching the water, giving the bird the appearance of running or walking on the surface of the ocean. The Fork-tailed Storm Petrel has a forked tail giving it its species name furcata, from the Latin furcatus.
NESTS IN ISLAND BURROWS
Most Fork-tailed Storm Petrels nest on small islands south of Alaska and in the Aleutian Island chain.
They excavate a long burrow and deposit a single white egg at the end of a small branch tunnel. The main burrow can be shared by several pairs, but each will clear their own side burrow. They can also re-use borrows of other birds such as puffins.
Both sexes incubate the egg with hatching averaging in about two months. For both incubation and feeding, the parents take shifts as the other flies long distances from the island nest to cold water over the continental shelf. To reduce the risk of predation all flights during the breeding period are at night with the parent returning in darkness. The young are fed a regurgitated oil and food mixture until they can handle partially digested fish, and fledge in about 60 days after hatching. (Kaufman). They go to sea to begin foraging for themselves.
GROWING IN NUMBERS
The Fork-tailed Storm Petrel is a common bird in the Northern Pacific Ocean. Population numbers are strong with estimates of 5-10 million birds worldwide. Most breed south of Alaska, but there are colonies off Russia. There is also a breeding colony on Tatoosh Island in Washington. In some areas the population may be increasing as introduced predators such as rats and foxes are exterminated from islands as part of a management plan (Dee and Silva).
Photo credit Andy McCormick. References available upon request from amccormick@eastsideaudubon.org.