Thursday, July 9, 2015

West Coast shearwater flight style identification

You prepared for your pelagic trip for months. You memorized all the subtle plumage characteristics in your field guides. When your trip reached the point where shearwaters were swarming around the boat, you noticed something disconcerting. Even with your binoculars, the shearwaters were hard to tell apart. The boat was bouncing, the birds would disappear behind swells, they would cross over to the other side of the boat where you were looking right into the sun's glare. You just couldn't consistently make out the plumage details to make a positive identification.

Shearwaters

And yet, one of the guides, volunteering to do the messy chumming, would barely glance up from her duties--without binoculars--and confidently announce the ID of a little dot-of-a-bird over a quarter mile away! And not just once, but repeatedly!

She either has inhumanly keen eyesight, or (gasp!) is NOT using the Peterson system of patternistic plumage characters for bird identification!



Shearwaters fly by interspersing flapping and dynamic soaring with wings stuck stiffly out to the side. Size, structure, and species-specific flapping behavior combine with range and seasonality so that most species can be identified simply by the way they fly. As far away as you can see a shearwater flap its wings and observe its glide path, that's how far away you can identify it! You don't need to see anything else. Color and plumage patterns of the bird simply do not matter, except for a couple of "fly-a-like" pairs.

All you need is 10 seconds

In 10 seconds (or less) you can watch the flight of a shearwater and determine its flight style pattern. On the West Coast there are 3 abundant shearwater-like birds making up most of the birds you'll see: Sooty Shearwater, Pink-footed Shearwater, and Northern Fulmar. Learn the flight patterns of these 3, and then keep a lookout for any bird that flaps and glides with a different pattern.


Sooty Shearwater: Repetitive flapping and graceful gliding on narrow wings. In calm conditions normal flight is 3-7 quick shallow flaps and a sustained glide of about 4 seconds, low along the water. In higher winds there is less flapping and higher arcs, sweeping up gracefully in a banked glide, then gliding low in a wave trough before repeating with a few quick flaps low along the water and arcing up again. Sooty Shearwaters tend to glide in a straight line.

Pink-footed / Flesh-footed Shearwater: The common Pink-footed Shearwater (and quite rare Flesh-footed Shearwater) is a bigger bird than Sooty Shearwater. It flies higher off the water with deep, slow wing beats ("lumbering," Stallcup 1990) and longer relaxed glides. The wings are long and broad. In moderate winds it wheels up in a slow arc above the horizon for several seconds reminiscent of an albatross.

Northern Fulmar: Longer bouts of flapping and gliding than Sooty Shearwater on shorter arched wings with rapid and shallow wing strokes. Unlike most shearwaters (especially Sooty) fulmars often flap at the high point of their arcing glides. "If it flaps while up in the air it is a fulmar" is a good maxim. Another characteristic is that fulmars often wheel around and change direction while in their extended glides, unlike Sooty Shearwaters.

Buller's Shearwater: They sweep up steeply and then gracefully glide downward, hardly flapping at all. Long glides on wings held forward at the wrist and accentuated by the long tail give the flight a most graceful appeal. Alternatively, groups will sometimes participate in synchronized flying with deep, slow wing strokes, flapping and gliding in unison ("languid and graceful," eNature.com 2003). Fall migrant on West Coast.

Short-tailed Shearwater: Erratic flight. Often similar to Sooty Shearwater, but wing strokes more rapid and swift-like ("snappier," Stallcup 1990) usually with more flapping and less gliding and arcing. This bird often makes darting direction changes and may rock from side to side while flapping (alternately showing you its back and then belly)--both traits that separate it from Sooty Shearwater. If the flight of Sooty Shearwater is consistently repetitive and straight, the flight of Short-tailed Shearwater is more rapid, frantic, and erratic. Uncommon late fall/winter migrant on West Coast.

Black-vented / Manx Shearwater: Tiny shearwater flies in a rather straight line with rapid deep wing strokes ("fluttery," eNature 2003). The glide often appears as little more than a "missed" wing beat. Black-vented is common in fall right along the California coastline. Manx is very rare anywhere on the West Coast to Alaska, also usually quite near shore.



Quoted references: 

eNature.com accessed originally for unpublished manuscript of this topic in 2003.

Stallcup, Richard W. "Ocean Birds of the Nearshore Pacific," 1990.