Fork-tailed storm petrel
Kingdom
Phylum
Class
Family
Genus
SPECIES
Oceanodroma furcata

The fork-tailed storm petrel (Hydrobates furcatus ) is a small seabird of the storm petrel family Hydrobatidae. It is the second-most abundant and widespread storm petrel (after Leach's storm petrel) and is the only bird in its family that is bluish-grey in colour.

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The fork-tailed storm petrel is pelagic, spending up to 8 months in the northern Pacific Ocean. They only return to land to breed, where they nest in a single colony. Their nests can be found in a rock crevice or small burrow, where a single egg is laid. Their breeding range is along the coast of the northern Pacific Ocean, extending from northern California to northeast Asia.

They mainly feed on planktonic crustaceans, small fish, and squid, but also consume offal. Similarly to other storm petrels, they forage by picking food off the surface of the water while in flight.

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Te

Terrestrial

Co

Congregatory

So

Social

Mi

Migrating

F

starts with

Appearance

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.

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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.

Males and females of this species are generally very similar in colour and size. Juveniles also resemble adults with the exception of having a less noticeable notch in their tails.

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Distribution

Geography

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 Outher Hebrides, Scotland.

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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.

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.

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Fork-tailed storm petrel habitat map
Fork-tailed storm petrel habitat map
Fork-tailed storm petrel
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Habits and Lifestyle

Seasonal behavior
Bird's call

Diet and Nutrition

Like other storm petrels, the fork-tailed storm petrel mainly feeds on crustaceans and fish near the surface of the ocean, including amphipods, myctophids, shallow-water fish (such as greenling and sablefish), copepods, decapods, and squid. They are also extremely opportunistic and can be seen scavenging on fatty tissue of dead marine mammals and also trailing behind fishing boats.

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Fork-tailed storm petrels have a well-developed olfactory system and heavily rely on odour to scout for food, so often they are the first birds to arrive at a pungent food source. When at the source, these birds seize their prey by fluttering across the water surface and may occasionally dive to depths of 0.6 m.

Like other Procellariiformes, the fork-tailed storm petrel produces stomach oil from its digested food and stores it in its proventriculus, a section of the bird's digestive system. This oil permits these birds to go for a long time without food, but also allows them to transport nutrient-rich food back to their chicks from distant sources.

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Mating Habits

Like other species, fork-tailed storm petrels spend most of their time out at sea and only return to land to breed around late March to early April. To avoid predation and harassment by gulls, these birds only enter the colony at night and depart before sunrise.

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The fork-tailed storm petrel builds its nest in rock crevices or small burrows on isolated islands. Courtship consists of vocalizations and aerial displays, often lasting for several weeks. Once established, pairs will remain together for the rest of the breeding season and if they are successful, continually use the same nest year after year. Females will lay a single white egg directly on the floor of the burrow, and both parents will incubate it for around 50 days. Once the egg hatches, the adult keeps the chick warm using its brood patch for the first five days. Once able to thermoregulate for itself, the parents then leave the chick, only returning to feed it one every one to four nights. After two months of slow growth, the petrel chick will finally fledge and leave the burrow.

Living in areas with severe climatic conditions, fork-tailed storm petrels have many adaptations to ensure breeding success. Eggs can be left unattended up to 7 days and still successfully hatch, whereas chick growth rates can be adjusted to being faster or slower depending on food supply, rather at a constant rate like many other birds.

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Population

Conservation

Being widespread and abundant, the fork-tailed storm petrel is not threatened with extinction. However, humans impact their life history in many ways.

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As a species that feeds on surface material and follows ships, this storm petrel often ingests oil and plastic with their food items. Surprisingly, the fork-tailed storm petrel is relatively unaffected by the toxicity of oil, as their natural diet contains substances that are very chemically similar. Plastics also do not severely affect the birds because they can be regurgitated after ingestion.

In contrast, being a top marine predator, fork-tailed storm petrels are susceptible to bioaccumulation. High lead concentrations have been found in the bones of petrels, and DDT can cause eggshells to become dangerously thin.

The greatest threats that face fork-tailed storm petrels today are global climate change and introduced species. An increased severity of storms makes foraging more dangerous, decreasing the chances that an adult will return to the colony. The introduction of mammals also adversely affect storm petrels, where raccoons and river otters prey upon nests, and rabbits increase soil erosion and compromise the structural integrity of burrows.

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References

1. Fork-tailed storm petrel Wikipedia article - https://en.wikipedia.org/wiki/Fork-tailed_storm_petrel
2. Fork-tailed storm petrel on The IUCN Red List site - https://www.iucnredlist.org/species/22698572/168979865
3. Xeno-canto bird call - https://xeno-canto.org/157187

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