Short-tailed Shearwaters
The ship moved into Bristol Bay a few days ago where the highlight has been an early Sabine’s Gull on 28 April. The bird numbers dropped dramatically after we left the deep waters west of Bering Canyon and entered the shallower waters of Bristol Bay. However, the last two days transiting deep water (26-27 April) were great and produced 2 more Mottled Petrels and 2 Leach’s Storm-Petrels–both of which are exclusively found over deep water. We also recorded 4 Red-legged Kittiwakes on this transit. There have been nice numbers of Short-tailed Shearwaters, both over deep water and in the shallower waters of Bristol Bay. Many of the shearwaters have been occurring in tight flocks of 30-50. Watching Short-tailed Shearwaters maneuver in a 30 knot wind is about as good as it gets!
Short-tailed Shearwaters Puffinus tenuirostris in Bristol Bay, 29 April 2009.
When compared to the similar Sooty Shearwater, note the steep forehead and shorter, thinner bill of the Short-tailed. Contrary to popular belief the “underwing flash” of a Sooty is not a reliable field mark for separating the two species. Short-tailed Shearwaters can show a flashy underwing (see top photo), especially when seen in bright light as these birds were. On a Sooty Shearwater, however, the brightest part of the underwing is the underwing covert panel and these bright underwing coverts contrast with the bird’s darker flight feathers. The underwing of a Short-tailed Shearwater is more uniform and can range in coloration from dark to light. When Short-tailed Shearwaters show a pale underwing it is a uniformly pale, or “flashy,” underwing and the flight feathers, especially the primaries, are also pale. In the top photo of the two Short-tailed Shearwaters note how the paleness of the underwing extends onto the primaries, which don’t contrast with the under-primary coverts as they would in a Sooty. Structural clues and flight styles are also extremely important, especially when the two species are seen together.
Click here for an excellent article (with excellent photos) by Greg Gillson, published in Birding magazine, which details the seperation of these two species.
