Fork-tailed Storm-Petrel
Hydrobates furcatus
Unique among storm-petrels in having an entirely silvery-gray plumage. Aside from overall plumage color, look for contrasting dark underwings, dark mask around eye, and deeply forked tail. Breeds on offshore islands across the North Pacific, from Japan to California. Fairly common over cool water, often not far from shore. Found singly or in large flocks, often mixed with other storm-petrels.
Identification
The fork-tailed storm petrel is small seabird that is 20 cm in length with a wingspan of 46 cm. Its foraging behaviour resembles other storm petrels, where it flies with short, stiff wingbeats close to the surface of the water.<p>Despite its name, the forked tail in this bird is not always visible. The distinguishing feature of fork-tailed storm petrels is their overall bluish-gray plumage. They generally have a paler underside, which contrasts the darker colours under their wings. They also have a dark gray forehead, a black ear patch, and a small, black bill. Other storm petrels are significantly darker, such as the similar looking ashy storm petrel. However, fork-tailed storm petrels from southern populations are somewhat darker than those in the north.<p>Males and females are generally very similar in colour and size. Juveniles also resemble adults with the exception of having a less noticeable notch in their tails.<p>They are generally silent and only call when entering their breeding colony at night. Their most common call is a 3- to 5-note, raspy "ana-ana-ana", heard from both sexes. This is especially intense during courtship, where their calls are accompanied by elaborate aerial displays. A higher-pitched, single note call is typically emitted by males, and it is used to locate females in noisy colonies and to maintain the pair bond.
Taxonomy
The fork-tailed storm petrel was formally described in 1789 by the German naturalist Johann Friedrich Gmelin in his revised and expanded edition of Carl Linnaeus's Systema Naturae. He placed it with the petrels in the genus Procellaria and coined the binomial name Procellaria furcata. Gmelin based his description on the "fork-tailed petrel" that had been described in 1785 in separate publications by the English ornithologist John Latham and the Welsh naturalist Thomas Pennant. It is now one of 18 species placed in the genus Hydrobates that was erected in 1822 by the German zoologist Friedrich Boie. The genus name combines the Ancient Greek hudro- meaning "water-" with batēs meaning "walker". The specific epithet furcatus is Latin meaning "forked".<p>Two subspecies are recognized:<p>The major differences between the two subspecies are slight size and plumage differences, where southern populations appear somewhat smaller and darker. Southern populations also begin and end their breeding season earlier than their northern counterparts. However, no molecular genetic analysis has been conducted to discern the two subspecies.<p>The species was formerly assigned to the genus Oceanodroma before that genus was synonymized with Hydrobates.
- Scientific name
- Hydrobates furcatus
- Authority
- (Gmelin, JF, 1789)
- Order
- Procellariiformes
- Family
- Hydrobatidae
- Genus
- Hydrobates
Range and habitat
The range of the fork-tailed storm petrel is estimated to cover 22,400,000 km2 with over 6,000,000 individuals occurring globally, making it the second-most widespread and abundant storm petrel. During the breeding season, the fork-tailed storm petrel form dense colonies on islands throughout northern California, Oregon, Washington, British Columbia, Alaska, and northeast Asia off the Kamchatka Peninsula. Most of their population is concentrated in Alaska, notably in the Bering Sea near the Aleutian Islands. Their southernmost colony is on Little River Rock in Humboldt County, with a population of 200 individuals. It was reported in July 1939 that fork-tailed storm petrels were breeding on the Flannan Isles, Na h-Eileanan Flannach, which are about 35 km west of the northern tip of the Outer Hebrides, Scotland.<p>Their nesting habitat varies, ranging from bare rock to forests. They typically build their nests under rock crevices or roots, or burrow into soft ground with low-growing vegetation.<p>As they frequent the open ocean, little is known about fork-tailed storm petrels outside of the breeding season. They have been frequently sighted off the Californian coast, making them the most northerly distributed storm petrel during the winter. Sparse sightings also indicate that they forage as far south as Hawaii.
- Breeding range
- PO : islands off n Kuril and Commander Is. (se Russia), Aleutian Is., and Gulf of Alaska to n California
- Non-breeding range
- to e coast of Japan, s Sea of Okhotsk, n Bering Sea, and c California coast
- Migration
- Complete migrants
Behavior
Migration pattern: Complete migrants.
Conservation
Population trend: rising.
- Population trend
- rising
Photos
Distribution
Bird Calls
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