Identification of 'Black-And-White' Storm-Petrels of the North Atlantic

Identification of ‘black-and-white’ storm-petrels of the North Atlantic Robert L. Flood and Bryan Thomas ABSTRACT This review article consolidates identification criteria for the six species of ‘black-and-white’ storm-petrel recorded or claimed in the North Atlantic: European Storm-petrel Hydrobates pelagicus,Wilson’s Storm-petrel Oceanites oceanicus, Leach’s Storm-petrel Oceanodroma leucorhoa, Madeiran Storm-petrel O. castro, Black-bellied Storm-petrel Fregetta tropica and White- bellied Storm-petrel F. grallaria. Established knowledge is updated with fresh insights and illustrated with instructive digital images.We have two aims: (a) to support County Recorders in Britain now responsible for evaluating Wilson’s Storm-petrel submissions; and (b) to bring to a wider international audience current understanding about identification of North Atlantic ‘black- and-white’ storm-petrels.The article has two main sections: (a) a general discussion about identification of the storm-petrels under review; and (b) detailed species accounts, and information on how each species can be distinguished from the other five species (though white-bellied Fregetta storm-petrels remain problematic). A template that outlines our view of what constitutes a sound submission of a reportable ‘black-and-white’ storm-petrel is proposed.The main text is supported by ten appendices covering size illusion and exaggeration, factors of scale, angle of view, descriptive terminology for flight behaviour, chum and chumming, and wear, moult and bleaching. We focus on vessel-based observation since, realistically, this is the optimal means of getting to grips with storm-petrels in the field and is the main source of our experience. Land-based observation rarely affords the views essential to apply the finer points of this presentation. An observer who has once had the good fortune of watching the two species [Wilson’s and Leach’s Storm-petrels] together can thereafter distinguish them almost as far away as the birds can be seen. (Murphy 1915) bservation and identification of of pelagic trips into the Western Approaches tubenoses (Procellariiformes) became aboard MV Chalice (with Harrison, from 1986 O‘fashionable’ in Britain in the 1980s to 1988), and on RMV Scillonian III with publication of Peter Harrison’s two seabird (1989–2004). These pelagic trips enabled many guides (Harrison 1983a, 1987) and the advent birders to experience North Atlantic tubenoses © British Birds 100 • July 2007 • 407–442 407 Identification of ‘black-and-white’ storm-petrels at close quarters and made possible the rare Madeiran Storm-petrel O. castro. European opportunity to photograph them. In those ‘early breeds during the northern summer in the days’, Wilson’s Storm-petrel Oceanites oceanicus northeast Atlantic and the Mediterranean, win- was the Holy Grail that tempted many British tering mainly off the west coast of Africa. ‘listers’ to participate in what was for some a Wilson’s is a circumpolar breeder along the stomach-wrenching venture to sea. Antarctic coastline as well as on sub-Antarctic However, from 2000, observations from islands during the southern summer, and part regular short-range pelagic trips off the Isles of of this population winters in the North Atlantic Scilly between June and September established (another population breeds in the Chilean that Wilson’s is, in fact, a regular though scarce fjords). Leach’s breeds during the northern summer and early autumn passage migrant in summer in the northwest and northeast regions Scillonian waters, and is not a sacred rarity (see of the Atlantic and winters mainly in regions of Appendix 1). In 20 years, the status of Wilson’s tropical convergence (there are also populations Storm-petrel plummeted from Holy Grail to in the Pacific). Madeiran breeds throughout the one where it was no longer considered as a year in the tropical and subtropical Atlantic; it is national rarity (as from 1st January 2006; dispersive and/or migratory and recorded in the Rogers et al. 2005). Suddenly, assessing reports western Atlantic from Brazil to Canada (there of Wilson’s became the responsibility of County are also populations in the Pacific). However, to Recorders, but there has been no recent sub- the north and east of its Atlantic breeding stantive consolidated identification update on range, Madeiran is an extreme vagrant to Wilson’s and similar so-called ‘black-and-white’ western Europe, except Portugal where there is North Atlantic storm-petrels to aid decision- a relatively small offshore breeding colony, esti- making at a county level. mated at c.50 pairs by Brooke (2004), and Furthermore, interest in storm-petrels has c.200–400 pairs in BWPi (2006). escalated in tandem with multiplying pelagic In western Europe, including Scandinavia, trips from many ports, on both sides of the vagrant Madeiran Storm-petrels have been North Atlantic. Knowledge has accrued about recorded from Britain (one, November), where and when to see them, while the mix of Finland (one, January), France (one, August; chum and methods of chumming have two, October), Ireland (one, October), Spain improved, bringing more storm-petrels even (singles in January, February, June and closer to observers and photographers (see November and two in July), and Switzerland Appendix 2). The combination of more pelagic (one, December) (Appendix 4). The data are trips, close proximity of storm-petrels and difficult to interpret because of the limited improvements in digital photography has numbers, while there is a complication with yielded superb images of storm-petrels at sea, Madeiran Storm-petrels breeding in the Azores, including many published for the first time where two distinct populations ‘time-share’ here. Insights into the identification of storm- burrows, each having non-overlapping breeding petrels have arisen through critical analysis of and dispersal periods (Friesen et al. 1998; Mon- digital stills and videos in combination with at- teiro & Furness 1998; Sangster 1999). The data sea observations. Conversely, unhelpful myths tentatively suggest that Madeiran is most likely have been propagated (see Appendix 3). So, in to occur as a vagrant in western Europe during addition to supporting local recorders in the storm-prone months from October to Britain, there is an international need for a February (often among other wrecked review article on ‘black-and-white’ North seabirds). Pelagic or land-based (tape-lured) Atlantic storm-petrels, integrating established records in summer for Spain and France may knowledge with fresh insights and new photo- relate to ‘wanderers,’ probably from the small graphic material. colony off Portugal but conceivably from another, larger North Atlantic colony. North Atlantic ‘black-and-white’ storm-petrels In addition, a Black-bellied Storm-petrel Four species of ‘black-and-white’ storm-petrel Fregetta tropica, presumably from the South occur regularly in the North Atlantic: European Atlantic populations, was seen and pho- Storm-petrel Hydrobates pelagicus, Wilson’s tographed c.70 km southeast of Oregon Inlet, Storm-petrel Oceanites oceanicus,Leach’s North Carolina, on 31st May 2004 (Guris et al. Storm-petrel Oceanodroma leucorhoa, and 2004). Another was seen and photographed 408 British Birds 100 • July 2007 • 407–442 Identification of ‘black-and-white’ storm-petrels nearby in the Gulf Stream off Cape Hatteras on identification unfolds as follows. Size, structure, 16th July 2006 (www.patteson.com). A White- plumage, and flight behaviour at first sight bellied Storm-petrel F. grallaria was reported combine into a whole first-interpretation, or north of the Cape Verde Islands on 17th August ‘jizz’. Jizz interpretation facilitates a ‘first stab’ at 1986 (Haase 1988; Clarke 2006). However, the identification: for example, ‘Oceanodroma at the description is brief and there is some doubt back of the slick!’ or ‘Oceanites-like “stormy” whether Black-bellied can be excluded (BWPi approaching from downwind!’ Dunne (2006) 2006). Moreover, there is confusion in the liter- attempted to convey jizz using catchphrases that ature regarding the white-bellied Fregetta are familiar to all. Those relevant to this article storm-petrels that breed in the Tristan da include: Wilson’s ‘dances with waves’, Leach’s is Cunha group (here taken to include Gough the ‘crazed or drunken Nighthawk of the sea’, Island). It is possible that a population of white- and Madeiran is the ‘plain dark storm-petrel’ bellied Black-bellied Storm-petrels breeds (p. 112). Similes also offer an effective way of alongside a population of White-bellied Storm- capturing the essence of a storm-petrel (table petrels, making the field identification of any 1). The idea of using catchphrases and similes white-bellied Fregetta storm-petrel in the North to summarise the quintessential character of a Atlantic extremely difficult (Appendix 5). storm-petrel can be very effective but there are Nonetheless, both Fregetta storm-petrels are caveats. First, jizz interpretation breaks down in potential vagrants to British waters. extreme circumstances at sea, such as during strong and gusty winds. Second, jizz is modified Identification when the bird’s flight feathers are heavily worn At-sea identification of seabirds involves unique and/or in moult (Appendix 6). Third, jizz inter- difficulties. Encounters are often extremely pretation alone, like pigeonholing, runs the risk brief; on all but large and steady vessels tele- of over-simplification. Hence, there also is need scopes are redundant;

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