Back in the Gulf: Tricks of the Trade

May 19, 2011

Wilson's storm petrel, courtesy of Lt. Elizabeth Crapo/NOAA

Seabird identification, especially from a pitching and rolling ship, is not easy. First of all, one has to throw away almost all of the tried-and-true methods that we use on dry land. Forget about using color, moving to a better vantage point, or listening to a song or call notes for clues.

Sometime during the late 1970s, I first learned just how difficult it was to even get a seabird into the field of view of my own binoculars. A friend and I had driven overnight from Tennessee up to Ocean City, in order to go out into the Atlantic Ocean during late May to see pelagic seabirds. Richard Rowlett was then chartering local fishing head-boats, loading them up with enthusiastic birders. (At that time, such excursions were still quite a novelty, whereas today one can select from an extensive menu of seabird trips on both Atlantic and Pacific coasts.)

Typical of the North Atlantic, my first pelagic excursion was a very bumpy ride. When a Wilson’s storm-petrel or Cory’s shearwater came into view, it never stayed in my binoculars long enough. I could not keep my balance; some surprise motion of the boat would knock me off tracking the bird. My main memory of that first experience is giving up, and trying to view the closest birds with the naked eye, hands clasped tightly to the rail, relying upon the word of others as to what I was actually seeing.

But experience finally teaches. For pelagic seabirds, one has to rely mostly on subtle cues. These include the bird’s shape and silhouette, flight behavior, and any contrasting pattern of dark and white. The truth is, we rely a great deal on how a seabird behaves to pin it down to species. Does it fly in a straight line? Or does its path over the sea rise and fall, like a rollercoaster? Does it look short-winged and long-bodied, with a labored flight? If yes, it’s an Audubon’s shearwater. If instead it looks long-winged and short-bodied, with a bounding flight, it’s a Manx shearwater. Is that storm-petrel flapping briefly, and then gliding on bowed wings? It’s a band-rumped storm-petrel. Does it have a more fluttery flight, with almost no glides? It’s a Wilson’s storm-petrel. And so on.

Sooty shearwater, courtesy of NOAA

The best thing I can do, aside from wishing for calm seas, is to first pick my observation point on the ship carefully. In other words, select a vantage point where the lighting best helps give away a bird’s identity. During high overcasts, the lighting is optimal, because the entire bird, top and bottom, can be evenly lit. But if there is any glare early or late in the day, I try to place myself where the birds are back-lit, with the sun over my shoulders. This position is especially good for picking out light or dark-and-white seabirds. For small, all-dark species like storm-petrels, I try to find lighting that makes the ocean surface look relatively even and lighter, the better to pick out these small, dark specks winging their way just over the waves. During mid-day, when lighting can be very harsh, I use the horizon to try to detect any birds that cross the line contrasting sea and sky.

If I can get a glimpse in good light, just a few seconds, I can almost always tell what I am seeing. If all goes well, medium size and larger birds can be identified up to a kilometer away. But there are always some birds whose ID just confounds us…the mystery birds. Like fishing tales, we too have our nautical stories of the “ones that got away.”