Bermuda Petrel or Ashy Storm-Petrel?
Here's how to tell the difference
Bermuda Petrel
Ashy Storm-Petrel
Bermuda Petrel
Pterodroma cahow
Also known as: Cahow
General appearance
The Bermuda Petrel, also known as the Cahow, exhibits a graceful maritime silhouette with a distinctive coloration that aids in identification. Its plumage is primarily dark gray on the wings and back, contrasting with the predominantly white underparts, creating a striking appearance. The face features a white forehead that connects to a collar of darker feathers around the nape, while the bill is slender and black, adapted for catching prey in its oceanic habitat.
Male vs female
In terms of physical appearance, there is minimal sexual dimorphism between male and female Bermuda Petrels. Both sexes share similar plumage patterns, size, and coloration, making it challenging to distinguish between them in the wild based solely on appearance. Behavioral observations during breeding seasons may offer more accurate ways to differentiate them as both sexes contribute equally to incubation and chick-rearing.
Juvenile
Juvenile Bermuda Petrels bear a close resemblance to adults but can be distinguished by slightly duller and more uniform plumage. The gray coloration on their wings and back lacks the subtle iridescence seen in adults, and their facial features may appear more subdued. Over time, as juveniles mature, they molt into the sharper, more contrasty plumage of adulthood. Despite these differences, distinguishing them at sea requires careful observation due to the similarity in their size and overall appearance.
Size
15.7 in/4.0 - 7.0 oz
There's more to learn about Bermuda Petrel
View full detailsAshy Storm-Petrel
Hydrobates homochroa
Ashy Storm-Petrel Recognition Guide
General appearance: The Ashy Storm-Petrel is a small, slate-gray seabird notable for its uniformly ashy coloration without any striking patterns or contrasts. This bird typically measures about 18 to 20 centimeters in length with long, slender wings spanning approximately 43 to 47 centimeters. Its plumage has a soft, sooty color throughout, mirrored by dark brownish hue in its long, slightly forked tail. The bird's head, back, wings, and upper parts are varying shades of ashy gray, lending it camouflage against the ocean's murky horizons. Male vs female: Both the male and female Ashy Storm-Petrels showcase similar morphologies and plumage characteristics. There are no conspicuous differences, and thus, distinguishing the sexes based on appearance alone can be challenging. Both sexes share identical coloration and size, making external identification in the field infeasible without behavioral context or genetic analysis. Juvenile: Juvenile Ashy Storm-Petrels bear a close resemblance to adult birds with only subtle differences in appearance. They generally display slightly paler or duller plumage and may lack the full depth of coloration seen in mature birds. As juveniles age, they gradually acquire the adult's consistent ashy gray tone, completing the transition in several months as they mature in the marine environment.
Size
7.1 - 8.3 in/1.2 - 1.9 oz
There's more to learn about Ashy Storm-Petrel
View full detailsHow to tell the Bermuda Petrel from the Ashy Storm-Petrel
Visual differences
The Bermuda Petrel is larger, with a length of about 16 inches (40 cm) and weight ranging from 4 to 7 ounces (113-198 g), featuring dark gray wings, a white underbody, and a white forehead with a slender black bill. In contrast, the smaller Ashy Storm-Petrel measures around 7 to 8 inches (18-21 cm) and weighs 1.2 to 1.9 ounces (34-55 g), adorned in uniform smoky gray plumage with a slightly curved black bill, allowing it to blend seamlessly with foggy seas.
Key differences and behavior
The Bermuda Petrel and Ashy Storm-Petrel exhibit distinct behaviors and habitats. Bermuda Petrels are long-distance travelers nesting in Bermuda's rocky islets, engaging in synchronized twilight courtship flights and sharing incubation duties over 53 days. In contrast, Ashy Storm-Petrels inhabit California's coastal regions, nesting in secluded rocks or burrows, with males performing display flights at night. Their incubation lasts roughly 42 days, led by females. Both species are pelagic feeders, consuming small fish and squid, with Bermuda Petrels covering greater distances. Ashy Storm-Petrels often skim the surface and follow ships for food scraps. Despite their similar prey, Bermuda Petrels have a more variable diet with seasonal abundance influencing food availability, while Ashy Storm-Petrels maintain a consistent diet. The Bermuda Petrel, weighing 4-7 oz (113-198g) and measuring 15.7 inches (40 cm) long, is heftier than the Ashy Storm-Petrel at 1.2-1.9 oz (34-55g) and 7.1-8.3 inches (18-21 cm) long.
Still not sure? Here are more lookalikes!
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