Michael Tove has organized and led pelagic trips since 1988 and is the author/artist of "Guide to the Offshore Wildlife of the Northern Atlantic" due out November 2000. In the first of two articles about pelagic birding in the north Atlantic, Michael tells us about one of the best areas in the world to find Pterodroma petrels.

About 45 miles off the coast off North Carolina's Outer Banks, including the Hatteras National Seashore, the continental shelf drops off into the Atlantic abyss more steeply than anywhere else in North America. Transversing this region is the Gulf Stream, a river of Subtropical water that originates in the Caribbean Sea and flows to the north northeast until it collides with the southward flow of the Labrador Current. This event also occurs east of Hatteras. These three features define a region 5 miles wide and 75-100 miles long that is sometimes referred to as "Pterodroma Alley."

Specifically, this is the region of the shelf drop, starting at about 500 Fathoms (3000 feet) and progressing out to about 1200 Fathoms (7200 feet). It gets its name because it hosts the greatest diversity and numbers of gadfly petrels (genus Pterodroma) anywhere in the Atlantic Ocean north of the equator. Four species are seen regularly, one abundantly and short of visiting their breeding grounds, there appears to be no place in the world where they are commonly seen.

The Black capped Petrel (P.hasita) is by far the most common and the only one which is seen daily in large numbers. Although, they are known to occur year-round, pelagic trips to Pterodroma Alley at present, only occur from May through October. During this time, a typical trip to this region will result in about 100-300 birds per day, although counts of many more are not uncommon. Black-capped Petrels are usually first encountered in water depths of 300-500 Fathoms and reach their peak abundance in 500-800 Fathoms. However, during storms, they are regularly observed in much shallower water as the strong winds tend to move them inshore.

The Herald (Trinidade) Petrel (P. arminjoniana), first discovered in North Carolina in 1979 by museum staff, was not known to occur regularly until 1991. Since that time, the number of sightings has steadily grown and over the past 5 years, is expected in at least one of every three trips, with up to 3 individuals per day being seen. Roughly 80% of birds are dark morphs, having nearly or entirely dark underparts. The remaining 20% are light morphs, with mostly or entirely white underparts. Although they have been seen in water as shallow as 20 Fathoms (non-storm), Herald Petrels are typically encountered in water from 800-1200 Fathoms in the northern portions of the "alley" and perhaps 300 Fathoms shallower in the southern portions. However, these differences may be influenced by the usual pelagic trip itineraries. The vast majority of records are from May through August, also reflecting a sampling bias. However, occasional sightings into October do suggest that the species is not merely a summer visitor.

The Fea's Petrel (P.feae), was also found to be a regular visitor starting in 1991. However, unlike Herald Petrel, this species has a narrow window of occurrence. The bulk of observations are from late May through mid-June. Lack of trips prior to late May likely truncates earlier dates but the June diminishment is no artifact. This bird, while regular, is quite rare and spring sightings number about half to a third fewer than Herald Petrels. Nonetheless, it is expected on about 1 in 4 trips, usually singly but up to two per day have occurred. Their disappearance after June coincides with their appearance at their breeding grounds on Bugio Island off Madeira. The occasional late summer to early fall sighting are attributed to non-breeding individuals. In the alley, Fea's Petrels are most commonly observed in water depths of 800-1200 Fathoms, although they have been seen as shallow as 500 Fathoms.

The Bermuda Petrel (P. cahow) is the rarest member of the group in the alley, although recently the frequency of sightings has been on the increase. Bermuda Petrels are also one of the world's rarest seabirds, with a total population of some 200 individuals, though happily, increasing. There are too few sightings to reveal any certain pattern of occurrence although a slight majority of birds seem to occur in late spring. Several of the birds appeared to be adults in rather worn plumage. Although sightings have occurred in water depths from 100 to over 1000 Fathoms, it is likely that this is a deep water species, occurring in the same waters as Herald and Fea's Petrels.

As an example of what Pterodroma Alley can produce, from May 26-29, 2000, six separate pelagic trips successfully surveyed these waters. The results included (combined totals): Black-capped Petrel 800+, Herald Petrel 4-5, Fea's Petrel 2, Bermuda Petrel 3 (high). Over the course of a typical season, (app. 30-40 trips), observers should expect thousands of sightings of Black-capped Petrel, about 12-15 Herald Petrels, 3-5 Fea's Petrels and 1-2 Bermuda Petrels.

What else is possible? There are no other Pterodroma species which would be expected except as an extreme vagrant. However, a Mottled Petrel seen New York some years ago may have reached there through the alley, and the critically endangered Zino's Petrel, which breeds beside Fea's on Madeira, may also occur at some time in the future. The occurrence of a White-chinned Petrel in October 1997 and Yellow-nosed Albatross in February, 2000 (although not in the alley), raises the specter of visitors from the Southern Hemisphere. Regardless of those, for anyone who is enamored with the Gadfly petrels will surely enjoy a journey down "Pterodroma Alley."

Michael Tove has organized and led pelagic trips since 1988 and is the author/artist of "Guide to the Offshore Wildlife of the Northern Atlantic" due out November 2000.

Michael Tove, 303 Dunhagan Place, Cary, NC 27511

e-mail him at: mtove@deltaforce.net

To find out more details about some of Michael's trips go to his listing in our East Coast USA Pelagic Directory.

(Illustrations accompanying this article by Andy Birch)