Fork-tailed Storm-Petrel or Black Storm-Petrel?

Here's how to tell the difference

Fork-tailed Storm-Petrel image 1

Fork-tailed Storm-Petrel

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Black Storm-Petrel image 1

Black Storm-Petrel

Fork-tailed Storm-Petrel

Hydrobates furcatus

Fork-tailed Storm-Petrel Description

General appearance - The Fork-tailed Storm-Petrel is a small seabird measuring about 19 to 21 centimeters in length with a wingspan of approximately 44 to 47 centimeters. Its plumage is mainly gray with a pale head and a darker eye patch that provides a striking contrast. The forked tail is one of the most distinctive features, giving the bird its name. The wings and back exhibit a lighter silvery-gray tone, especially noticeable when seen in good lighting conditions. Male vs female - There is minimal sexual dimorphism in Fork-tailed Storm-Petrels, meaning males and females appear quite similar. Both genders exhibit the same general color pattern and size, making it challenging to differentiate between them based purely on external features. There is no noticeable difference in plumage coloration or tail shape between the sexes. Juvenile - Juvenile Fork-tailed Storm-Petrels closely resemble adults in their coloring and size, but they can be distinguished by slightly fresher and more uniform plumage. The feathers of juveniles are softer and may appear less worn compared to adults. As they mature, their coloration becomes more defined, and they adopt the same markings as the adults. Seasonal variations in appearance are minimal, as the species maintains consistent plumage throughout the year.

Size

7.5 - 9.4 in/1.6 - 2.1 oz

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

Visual differences

The Fork-tailed Storm-Petrel, weighing 1.6-2.1 oz and measuring 7.5-9.4 inches, has a distinctive pale grey plumage with a forked tail and wedge-shaped wings. In contrast, the Black Storm-Petrel is slightly larger at 1.2-2.1 oz and 8.7-9.8 inches, featuring uniform dark, almost black plumage. The Fork-tailed has a more prominent fork in its tail, assisting in identification, whereas the Black Storm-Petrel displays a less pronounced fork and is notable for its sleek, nimble appearance over the ocean.

Key differences and behavior

Fork-tailed and Black Storm-Petrels share a marine-based lifestyle but exhibit distinct behavioral traits. Fork-tailed Storm-Petrels, found in the colder North Pacific, are adapted to stormy conditions with their oily waterproof feathers, while Black Storm-Petrels inhabit warmer tropical eastern Pacific waters and are skilled at navigating around storms. Both species are pelagic, but Fork-tailed Storm-Petrels are more often seen in coastal areas during storms or breeding, unlike the seldom land-bound Black Storm-Petrels. Breeding-wise, both are monogamous and colonial, with Fork-tailed Storm-Petrels nesting on cold rocky shores and Black Storm-Petrels on warm isolated cliffs. Their diets of small fish and squid are similar, though their foraging aligns with different oceanic conditions—Fork-tailed in cold currents and Black in warmer upwellings. Neither species is attracted to typical bird feeders, depending entirely on marine resources.

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