Separation of Sooty and Short-tailed Shearwaters
by Greg Gillson,
copyright © 2000, 2001 by The Bird Guide, Inc. all rights reserved.

The separation of Sooty and Short-tailed Shearwaters can be quite an identification challenge for birders in the NE Pacific. These species can be quite similar--but there are differences. Both the National Geographic Society's Field Guide to the Birds of North America (Third Edition, 1999), and the National Audubon Society's The Sibley Guide to Birds (2000) mention differences in the text, but do not show the most different-looking birds. They opt to show similar-looking birds, stating: "most plumage differences subtle and overlapping." Most plumage differences are subtle. Therefore, a combination of characters should be used to identify these birds with more confidence.

For birders on the west coast of North America, the problem will be picking out a Short-tailed Shearwater from the thousands of Sooties that migrate past our shores, or spotting one swirling around the chum on a pitching boat during a pelagic birding trip. There are some Short-tailed Shearwaters that look very much like Sooties. There are some obvious Short-taileds, however, that look strikingly different from any Sooty Shearwater. Thus, this discussion concentrates on finding those individual Short-tails that are the most different from Sooties. Once you see obviously different birds you can begin looking for the key marks that will separate most birds in the field.

Behavior and flight style differences also help separate some birds. With practice, it is often these behavioral differences that catch your eye first, prompting closer inspection.

The identification characters below were gleaned from numerous encounters with known-identity birds feeding on chum at sea. As these birds would get up and fly around the boat and resettle, we could see that they flew differently and many had subtle, but consistent, plumage differences that were verified by photographs. On subsequent trips we could use these characters to help identify birds earlier and more readily.

Sooty Shearwater
Sooty Shearwater. Hold mouse over image until labels appear. Click photo for larger view.

Sooty Shearwaters are dark sooty gray-brown. The diagnostic mark for this species is the white feathering on the median and greater underwing coverts. The extent of white feathering varies slightly between birds, but the following is generally true. The largest extent of white is usually on the primary coverts. The lesser and marginal coverts are dark, creating a large dark wedge on the leading edge of the inner underwing. The flight feathers, underwing primaries and secondaries, are dark. The silvery-white underwing flash is thus restricted to the interior of the wing.

The characteristic flight is 3-7 quick, stiff-winged, flaps, low along the water, followed by a glide of 3-5 seconds. In stronger winds, the glide is arcing and banked. This pattern is repeated continuously. Even at a great distance birds can be identified by this habitual flight style alone.

Sooty Shearwaters are usually not very interested in chum (fish scraps and beef fat tossed from the boat to attract seabirds). They will fly past, though, and often sit down at the periphery of a feeding flock of gulls, fulmars, and albatrosses. Rarely do they join in a feeding flock and dive for food.

Short-tailed Shearwater
Short-tailed Shearwater (typical fall example). Hold mouse over image until labels appear. Click photo for larger view.

Short-tailed Shearwaters are also brownish-gray, but there is much variation. Some birds are all-dark. But many, perhaps especially in fall, have pale breasts, setting off a blackish hood. The main movement of Short-tailed Shearwaters past Washington and Oregon is from mid-September into January, or even to May. They peak from late October to early December. Breeding adults lay their eggs in late November in New Zealand. Thus, the birds we see in late fall and winter are not breeding adults, rather they are likely immatures. Perhaps it is the worn plumage on these younger birds that makes them appear so obviously hooded.

In comparison to Sooty Shearwater note the shorter and thinner bill (formerly called Slender-billed Shearwater), and slightly more prominent forehead and rounded head of the Short-tailed Shearwater. In direct comparison, the Short-tailed Shearwater is smaller with a shorter neck. Short-tailed Shearwaters really do have shorter tails and their feet extend well past the tail, but this is only a minor supporting mark, as other shearwaters can momentarily position their feet to appear longer than tail.

The under surface of the wing often appears all-dark. However, it may be pale or reflect a variable bit of silvery-gray, recalling Sooty Shearwater. But unlike that bird, this paleness includes more of the underwing coverts, and often includes the under-primaries and under-secondaries. On these pale-winged birds, the key mark is that the leading edge of the inner underwing (marginal coverts) appears pale.

On most birds the throat and upper breast is paler than the belly. In especially well-marked individuals the pale breast and darker head give the bird a helmeted appearance. Some birds, though, seem evenly dark with no contrast anywhere on the body.

The flight style of Short-tailed Shearwater is similar to that of Sooty Shearwater. However, the wing strokes are usually more rapid and swift-like, with more flapping and far less gliding and arcing. The bird often makes darting direction changes. The general impression is that of a more rapid, frantic, erratic, flight, rather than the usual smooth, repetitious, undulating, flight of Sooties.

Short-tailed Shearwaters are especially attracted to fish scraps and beef fat tossed from the boat. They dart in and out between the other larger birds and dive for sinking scraps.

Combination of characters used to identify a Short-tailed Shearwater in flight (ordered by characters often attracting first attention in the field):

  • rapid, erratic, flight, with less smooth gliding than the Sooties in the same wind condition
  • all-dark underwing linings or, conversely, extensive pale wing linings-especially onto the bases of the primaries or the leading edge of the inner wing
  • pale breast contrasting with dark head
  • feet hanging past tail
  • short, thin, bill, rounded head, short neck

Short-tailed Shearwater Short-tailed Shearwater

Short-tailed Shearwater. Pale example.

Short-tailed Shearwater. Dark example.

Scans of video of Short-tailed Shearwater by Greg Gillson in October 1999 off Newport, Oregon.

Short-tailed Shearwater

This Short-tailed Shearwater provided the basis for the drawings above. Notice the pale under primaries, which are always dark on Sooty Shearwaters. Also note the pale leading edge of the inner underwing. Many Short-taileds, though, show all-dark wing linings. The hooded appearance was obvious in the field. But it was the darting flight style as the bird swooped in behind the boat and dove for scraps that was most telling. (Click photo for larger view.)

Short-tailed Shearwater

More so than Sooty Shearwaters, Short-tailed Shearwaters tend to hold their wings open on the water. Perhaps because they are smaller than most of the other birds, they are always prepared to take an escaping flight. On the other hand, these birds dive frequently and "fly" underwater with open wings. Perhaps holding their wings open in this manner helps them dry. (Click photo for larger view.)

Photos of Short-tailed Shearwater by Tim Shelmerdine in October 2000 off Newport, Oregon.

Short-tailed Shearwater

Note the pale throat contrasting with dark head and nape. This shading gives the appearance of a dark helmet in flight on some birds. The bill is barely 2/3 the length of the head and thin. On a Sooty Shearwater the bill would be more like 7/8 the length of the head and thicker. Short-tailed Shearwaters often look shorter-necked than Sooties when they are sitting on the water. Also note that the wingtips extend at least a bill-length past the end of the tail. (Click photo for larger view.)

Short-tailed Shearwater

Most of the underwing on this bird is pale. The especially telling portion is the pale feathering on the leading edge of the inner underwing. The whitish chin and pale throat is also a trait of Short-tailed Shearwaters in fall off Oregon. The feet of Both Sooty and Short-tailed Shearwaters are usually dark, but can be pinkish, as with this bird. (Click photo for larger view.)

Short-tailed Shearwater

On this Short-tailed Shearwater notice that the pale wing linings form an extensive panel, extending onto the base of the primaries and especially onto the marginal coverts to the leading edge of the inner wing--something almost never shown by Sooty Shearwaters. The shorter neck, shorter tail with feet hanging behind, and the small wing span help complete the combination of characters necessary to verify the identification. Photo October 2001 by Bruce Craig.

Sooty Shearwater

The silvery wing feathers of the Sooty Shearwater are restricted to the greater and median coverts--especially on the primaries. The leading edge of the inner wing forms a dark wedge. This creates a very unique shape that is common to all Sooty Shearwaters and is rarely mimicked by Short-tailed Shearwaters. The tail is longer and more wedge-shaped than the tail on a Short-tailed. The wings are longer. Photo by Steve Shunk.

Short-tailed Shearwater

Short-tailed Shearwater with brightness and contrast adjusted to show the shape of the pale underwing panel. Some Short-tailed Shearwaters have entirely dark underwings. Photo October 2001 by Bruce Craig.

Sooty Shearwater

Sooty Shearwater with brightness and contrast adjusted to show the unique pattern on the greater and median coverts. Photo by Steve Shunk.

Short-tailed Shearwaters

A duet of Short-tailed Shearwaters. Notice that the left bird has an underwing indentifiable as belonging to Short-tailed Shearwater, while the rightmost bird has an underwing pattern nearly identical to that of Sooty Shearwater. Photo October 2001 by Bruce Craig.

Short-tailed Shearwaters

Nearly all the coverts are pale on this Short-tailed Shearwater. A Sooty Shearwater never shows this much general paleness. Photo provided by Phil Pickering.

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