Least Storm-Petrel or Fork-tailed Storm-Petrel?

Here's how to tell the difference

Least Storm-Petrel image 1

Least Storm-Petrel

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Fork-tailed Storm-Petrel image 1

Fork-tailed Storm-Petrel

Least Storm-Petrel

Hydrobates microsoma

General Appearance

The Least Storm-Petrel is a small seabird known for its compact form and distinctive flight pattern. Its plumage is predominantly sooty black or dark slate, which can appear darker under direct sunlight. On the upper wings and back, the dark feathering enhances the bird's streamlined appearance. The feet are webbed, aiding in swimming, and its beak is small and pointed, ideal for surface skimming. The tail is short and slightly notched, contributing to its agile maneuvering in flight.

Male vs Female

There is a marked similarity in the appearance of male and female Least Storm-Petrels, making sex determination challenging without close observation or scientific examination. Both sexes typically exhibit the same size and feather coloration, minimal sexual dimorphism is present. This similarity helps them avoid predators by making it difficult for them to be targeted as pairs or individuals.

Juvenile

Juvenile Least Storm-Petrels closely resemble adults in terms of shape and coloration, although they may appear slightly duller. Their feathers might lack the fully weathered sheen seen in mature individuals and could display more subtle sooty tones. Juveniles have shorter wings and may not demonstrate the same level of flight skill as adults, as they are still developing their flight capabilities and muscle strength.

Size

5.1 - 5.9 in/0.7 - 1.0 oz

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How to tell the Least Storm-Petrel from the Fork-tailed Storm-Petrel

Visual differences

The Least Storm-Petrel is smaller, weighing 0.7-1 oz and measuring 5.1-5.9 inches in length, with a uniformly dark, sooty plumage and a small, delicate beak. In contrast, the Fork-tailed Storm-Petrel is larger at 1.6-2.1 oz and 7.5-9.4 inches long, showcasing a pale grey plumage with a forked tail and wedged wings, and a sturdier beak. These differences in size, color, and tail shape are key identification features.

Key differences and behavior

The Least Storm-Petrel and the Fork-tailed Storm-Petrel exhibit distinct behaviors. The Least Storm-Petrel, weighing about 0.7-0.95 oz, is a warm ocean dweller, performing graceful wave-top foraging and engaging in nocturnal vocalizations for courtship in tropical and subtropical Pacific waters. They nest monogamously in secluded sandy or rocky burrows. In contrast, the Fork-tailed Storm-Petrel, at 1.6-2.1 oz, thrives in cold marine climates of the North Pacific, adeptly riding storm winds and waterproofing its feathers. They court with aerial displays, nesting in rocky coastal colonies. While both feed on small marine organisms, the Fork-tailed Storm-Petrel frequents colder, current-rich waters. Neither species visits feeders, reflecting their reliance on oceanic foraging.

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