Identification of white-rumped North Atlantic petrels

Peter Harrison

Leach's Petrel Oceanodroma leucorhoa and Storm Petrel Hydrobatespetagicus occur regularly off our coasts, mainly in the west and north, during

March to October. For many birders, autumn gales provide the only opportunity to witness these small, mainly dark and closely similar species. The recent, and most welcome, interest in autumn seawatching has inevi­tably led to claims of sightings of two other species: Wilson's Petrel Oceanites oceanicus and Madeiran Petrel Oceanodroma castro. The fifth member of the Hydrobatidae occurring regularly in the North Atlantic is the White-faced Petrel Pelagodroma marina, but that species is so distinct that it is not discussed here (see Cramp & Simmons 1977; Naveen 1981,1982; Harrison 1983).

This paper is based largely on my own field notes, written and sketched over a period of 20 years in the North and South Atlantic and the Pacific and Indian Oceans. All measurements are taken from Cramp & Simmons (1977). The discussion on identification is limited to typical examples occurring in the North Atlantic and does not take into account the Leach's Petrels in the Pacific, which vary from light-rumped forms to those with

continued...

161

162 Identification of white-rumped petrels

59. Wilson's Petrel Oceanites oceanicus. South Atlantic, January 1977 (Dave Monteith, Joint Services Expedition)

wholly dark rumps (Ainley 1980). Neither does it attempt to catalogue the possible identification pitfalls due to moult, feather abrasion, and so on. Nor does it include notes on similar extralimital species which occur outside the North Atlantic: see Naveen (1981 & 1982) and Harrison (1983) for notes on such species as Swinhoe's Oceanodroma monorhis and Fllliot's Petrels Oceanites gracilis.

The four species of white-rumped petrels occurring regularly in the North Atlantic are very similar. The combination of small size, similar plumage features, infrequent observation and less than optimum viewing conditions makes field identification difficult. Inexperienced birders may find it impossible.

Basic identification techniques

Despite general similarities, the four species—Leach's, Madeiran, Storm and Wilson's Petrels—all have diagnostic differences in structure and plumage which should allow experienced observers to reach a positive identification. Since these differences are subtle and slight, and because all observers see and identify birds differently, there will always be argument as to the best or most reliable way to assign a bird to species. My own approach to petrel identification is based on the awareness that they can be divided by structure and flight into two basic groups: (i) those with propor­tionately long and rather angular wings, and (2) those with shorter, more rounded wings.

Identification of white-rumped petrels 163

The first group, typified by the genus Oceanodroma, has proportionately long, rather angular wings, with pointed wing-tips and a rather tern-like flight. Leach's and Madeiran Petrels are included in this group. The second group comprises those species with proportionately short, rather broad wings, lacking a definite angle at the carpal joint, with a blunt or rounded wing-tip and a weaker more fluttering flight. This group includes Wilson's and Storm Petrels.

The difference in wing-shape between the two groups (fig. 1) is caused mainly by the difference in the lengths of the humerus (A) and ulna (B). In Oceanodroma species, these two bones are comparatively long, whilst in the shorter-winged genera (Oceanites in this case) they are shorter, and thus form a shorter, more paddle-like wing-shape.

Fig. 1. Diagrammatic representation showing the different length of the humerus (A) and ulna (B) in 'long-winged' and 'short-winged' petrels

The real problem in petrel identification is overcoming the practical difficulties of deciding whether the wing-shape is long and angular or short and rounded. The task is made more difficult by the vagaries of light, distance, angle, sea conditions, and so on. I overcome the problem by concentrating on 'freezing' the image of the wing-shape in my mind's eye when the wing is at the apex of its upward beat. This technique becomes easier with practice.

Once the wing-shape of the petrel under scrutiny has been ascertained, a combination of certain plumage features and tail-shape together with flight should enable reasonably accurate identification (given comparative experience). It is necessary to concentrate in particular on the following four aspects.

Rump pattern Rump patterns are often obscured by conditions or range; when visible, they can be diagnostic, but only when accurately recorded. It is of little use

164 Identification of white-rumpedpetrels

to record the rump as 'white, without a grey dividing line' (some Leach's seen off Britain could be so described). The shape of the rump is what must be recorded: look to see if it is narrow, extending across the body; square and large, seemingly always in view; V-shaped; and so on. Note also the degree to which the white of the rump extends onto the undertail-coverts and rear flanks. Any marks on the rump (e.g. grey dividing line or dark tips to the feathers) should, of course, also be recorded.

Tail-shape

Range and sea conditions normally prevent critical examination of tail-shape of most of the four species under discussion. Leach's Petrel, however, has a distinct fork to the tail, which is visible under certain conditions, even at moderate or long ranges. Viewed from a high, stable vantage-point, tail-shape is often easier to record than some guides indicate, especially using a modern telescope. With practice, individual observers become aware at what range they are able to discern the degree of fork or squareness of the tail under given conditions.

Flight and feeding behaviour

T h e type of flight behaviour can enable an experienced observer to identify some petrels at ranges when differences in structure and plumage features are meaningless. Flight must therefore be considered as a potentially important identification character; but a word of caution: it is fallible. Flight varies with wind direction and force, sea conditions and the physical state and activity of the bird under scrutiny. (It also depends on an

60. Wilson's Petrels Oceanites Oceanian, USA, August 1982 (Alan Brady)

Identification of white- rumped petrels 165

observer's ability to interpret such subjective and ill-defined terms as erratic, bounding, leaping, shearing, fluttering, and so on.) Always remember that, as most of our petrels are seen in gale conditions, their flight may be different from that described in popular guides, which normally refer to birds feeding or travelling in light or moderate winds.

Basic points to look for when concentrating on flight are type of course— straight, zig-zag, erratic, or bounding—whether it is slow or fast, the height above waves, the extent of gliding and the relative depth, height and speed of wing-beats. Also, when feeding, does the bird hold its wings flat and horizontal, slightly above the horizontal or in a deep ' V above the back? Does it foot-patter, walk, skip, hop, splash or jump across the surface?

Wing markings Paler edgings on the upperwing-coverts and underwing-coverts often form pale bars. On two species (Leach's and Wilson's) the upperwing bar is usually well developed; on Madeiran it is only moderately so; whilst on Storm it may not be evident even when viewed at close range. Storm Petrel has a variable but diagnostic white stripe on its underwing; some Wilson's also show a diffuse pale (but not white) stripe on the underwing.

Fig. 2. Four white-rumped North Atlantic petrels in flight: Leach's Oceanodroma leucorhoa, Wilson's Oceanites oceanicus, Madeiran Oceanodroma castro and Storm Petrel Hydrobatespelagicus

(Peter Harrison)

166 Identification of white-rumped petrels

Fig. 3. Uppersides of re­treating petrels, showing rump patterns with tails slightly fanned (PeterHarrison)

Although Leach's Oceano-droma leucorhoa and Wilson's Petrels Oceanites oceanicus both have prominent upper-wing bars, the wing-shape and rump pattern of'the two speeies are distinctly diff­

erent

Madeiran Petrel Oceanodroma cas-tro appears intermediate between Leach's 0. leucorhoa and Wilson's Petrels Oceanites oceanicus, but with less apparent upperwing bar and an even white rump. Storm Petrel Hydrobates pelagicus is the smallest and darkest of'the North Atlantic petrels, with little (if any) upper-wing bar, but a diagnostic under-

wing stripe

Madeiran Petrel

Storm Petrel

Once plumage features and tail-shape are added to the wing-shape of the petrel under scrutiny, identification should be straightforward (given comparative experience). In most sightings off Britain, the decision is relatively simple. If the wing is proportionately long and angular, with a definite bend at the carpal, coupled with an obviously paler upperwing bar, a forked tail and bounding, erratic flight: Leach's Petrel. If the wing is short, rather tapered at the tip, without a noticeable bend at the carpal, little or no paler upperwing bar, but a white stripe on the underwing and a square tail: Storm Petrel.

Identification of white-rumpedpetrels 167

If vagrants are also considered, Wilson's has a short, paddle-like wing-shape, lacking obvious angles, a pronounced upperwing bar and the most extensive side extension of the white rump to be found on any of the petrels discussed in this paper. Madeiran is more difficult to separate, having a moderately long wing, but with a broader and more rounded wing-shape. These characters are discussed in more detail later. There are obvious pitfalls to consider: range and moult can obscure upperwing bars and rump pattern; and moult can also alter the shape of the outer wing (e.g. Marsh 1980).

Species accounts The four species are illustrated in figs. 2 & 3, and the following notes treat them on a comparative basis, beginning with the short-winged group, Wilson's Petrel and Storm Petrel.

Short-winged petrels Wilson's Petrel Oceanites oceanicus SIZE Length 15-19 cm; wingspan 38-42 cm. At sea, appears intermediate in size between Storm Petrel and Leach's Petrel, al though some overlap with both.

PLUMAGE Appears generally blacker than either Leach 's or Madei ran , but slightly browner than Storm. Rump and uppertail-coverts pure white, extending broadly to include lateral undertail-coverts. Thus , at sea, r u m p appears as broad white curving band over tail, seemingly always in view and much more conspicuous than rump of Leach 's . Like that species, but unlike Storm,

6 1 . Wilson's Petrel Oceanites oceanicus, USA, Ju ly 1974 (Alan Brady)

upperwing usually shows pronounced pale ba r across coverts. Due to wing structure (fig. 1), wing bar usually appears shorter and broader than on Leach's . Many Wilson's Petrels show pronounced pale flush on underwing-coverts , which should not be con­fused with diagnostic white stripe on underwing of Storm.

WING-SHAPE AND JIZZ Wilson's Petrel has proport ionately short wing, with rounded wing-tip lacking definite angle on either leading or trailing edges. This character is more pronounced on trailing edge, which,

168 Identification of white-rumpedpetrels

dur ing glides, appears virtually straight. Tail short , square-ended, with rounded corners. Wilson's differs from other white-rumped North Atlant ic petrels in conspicuously long legs, which usually project beyond tail in travelling flight. This character visible at modera te ranges given reasonable condi­tions. Yellow webs (which can vary in colour and extent) are virtually impossible to ob­serve at sea unless at very close range. (In several thousand sightings, I have recorded yellow webs on only two occasions.)

FLIGHT Travelling flight : Wilson's has fairly

strong, direct course (though it occasionally veers from side to side), which may be up to 3 m or more above the waves. Bursts of rapid wing-beats are broken by short glides, which give flight recalling Swallow Hirundo rustica.

Feeding flight: The walking-on-water, foot-pat ter ing feeding flight of Wilson's, with wings raised high over back in V-shape, bill hanging down to water as it hops, walks and bounces slowly across the waves, is well documented in previous literature. No other North Atlantic petrel has a flight quite the same, nor docs any have such long conspic­uous legs. Habitual ly follows in ship's wake.

6 2 . Wilson's Petrels Oceanites oceanicus, USA, August 1982 (Alan Brady)

IDENTIFICATION SUMMARY Wilson's Petrel most closely resembles a Storm Petrel in its propor­tionately short , rounded wings which lack a definite angle on both leading and trailing edges. It is readily separable , however, by the broad pale bar across the upperwing-coverts; greater side extension of white rump; lack of variable, but distinct white bar on underwing; much longer legs; a higher, and much more forceful, direct travelling flight, utilising fewer, shallower wing-beats , with longer more frequent glides. The height, directness and vigour of flight is qui te distinct from that of Storm Petrel. By comparison, Storm Petrel is virtually black, with little (if any) upperwing bar, less side extension of white onto the undertail-coverts, a weaker, more fluttering bat-like flight, and diagnostic underwing.

Leach 's Petrel differs from Wilson's in rump pattern, long, rather narrow wings, with pointed wing-t ip, a definite angle on both leading and trailing edges, and a forked tail. The legs are also much shorter than those of Wilson's. Compared with Leach's, Wilson's has a more direct and purposeful travelling flight, with shallower, faster wing-beats, the wings rarely raised in high, tern-like posture, and shorter glides. Thus , flight lacks the bounding and erratic veering of Leach 's .

Made i r an Petrel differs from Wilson's in rump pat tern, more uniform upperwing colour and longer-tailed appearance . T h e wing is moderately long, and, although rather rounded at the tip, usually shows a definite angle on both leading and trailing edges. Madeiran also has a

Identification of white-rumped petrels 169

6 3 . Wilson's Petrel Oceanites oceanicus, Bermuda, April 1978 (Keith Pellow)

shearwater-l ike travelling flight, with longer wing-beating periods and longer glides on flatter wings.

Storm Petrel Hydrobates pelagicus SIZE Length 14-18 cm; wingspan 36-39 cm. Smallest Atlantic petrel, but largest examples equal smallest Wilson's Petrels.

PLUMAGE Darkest Atlantic petrel, appearing mostly sooty black at sea. Rump and upper-tail-coverts conspicuously white, extending just to lateral undertail-coverts. Rump appears as rectangular band over tail, always more conspicuous than on Leach's, but not so prominent as on Wilson's, which has greater side extension of white onto rear flanks and lateral undertail-coverts. Differs from all other Atlantic petrels in virtual absence of paler bar on upperwing-coverts, which, even at close range, may appear wholly dark. Underwing diagnostic, bearing distinct white bar of variable extent across coverts. Wilson's often shows diffuse paler (but not white) flush on undcrwiiig-coverts, whilst Leach 's and Madei ran show mostly dark underwings.

WING-SHAPE AND JIZZ Storm Petrel has pro­

portionately short, broad wing, with little or no bend at carpal joint, and rounded but slightly tapering tip. Tail appears short and square , with rounded corners. Unlike Wilson 's , legs are so short that they are rarely seen at sea and do not project beyond the tail in travelling flight.

FLIGHT

Travelling flight: Storm Petrel has rather weak, fluttering, bat-like flight, with almost con­tinual flapping interspersed with short glides, usually direct and low over waves.

heeding flight: Resembles Wilson's, but wings raised only midway over back, with short legs pattering on surface. Progression at such times slow, often stationary, and lacking Wilson's accomplished walking-on-watcr technique. In strong winds, often blown backwards or sideways many metres. Follows in wake, although perhaps never to extent that Wilson's does; frequently attends fishing vessels.

IDENTIFICATION SUMMARY Storm Petrel most closely resembles Wilson's in its proportionately short wings, which lack a pronounced angle on both leading and trailing edges. Separable from Wilson's and all other North Atlantic petrels by virtual lack of paler bar across upperwing-coverts (pale bar is most pronounced on fresh juveniles during au tumn) , diagnostic underwing pat tern, and fluttering bat-like flight. Compared with Wilson's, travelling flight more hesitant and weaker, with quicker wing-beats and shorter glides, rarely as high, strong or vigorous. The white side extension of rump is less extensive, and the legs are shorter.

By comparison, Leach's Petrel is larger than Storm Petrel, with proportionately longer, angular wings, pointed at tip and held bent at the carpal joint, with a prominent upperwing bar, forked tail and a duller Y-shaped rump which shows less side extension onto the flanks. The flight of Leach's is much stronger than that of Storm Petrel, more buoyant, on tern-like wings, with slower, deeper wing-beats accompanied by erratic changes of course, height and speed, interspersed with longer shearing glides.

170 Identification of white-rumpedpetrels

64. Storm Petrel Hydrobatespelagicus, Scilly, August 1979 (David Hunt)

Madeiran Petrel is larger and longer-winged than Storm Petrel, with difTerent rump pattern, a proportionately longer, slightly forked tail, more pronounced upperwing bar, distinctly different flight, and a dark underwing.

Long-winged petrels Leach's Petrel Oceanodroma leucorhoa SIZE Length 19-22 cm; wingspan 45-48 cm. At sea, appears larger than other white-rumped North Atlantic petrels, although some overlap occurs with both Madeiran and Wilson's Petrels.

PLUMAGE Appears generally dark greyish-brown to brownish-black, paler than either Storm or Wilson's Petrels. Rump and upper-

tail-coverts white, with minimal side extension to flanks and lateral undertail-coverts. At very close range (no more than about 200 m), diagnostic grey dividing line down centre of rump may be visible. Under most viewing conditions, however, rump appears distinctively V'-shaped and com­paratively duller, less striking or apparent than those of Wilson's, Storm or Madeiran Petrels. Upperwing usually shows pro-

65. Leach's Petrel Oceanodroma leucorhoa, Dorset, November 1982 (Peter Harrison)

Identification of white-rumped petrels 171

6 6 . Leach 's Petrel Oceanodroma leucorhoa, Bermuda, J u n e 1977 (Keith Fellow)

nounced paler bar across coverts, often visible at ranges when white rump is not. (By comparison, Madciran usually shows dis­tinct white r u m p at ranges when its pale upperwing bar is invisible.)

WING-SHAPE AND JIZZ Leach's has propor­tionately long, ra ther narrow wing, with obvious angle at carpal joint , corresponding angle on trailing edge, and decidedly pointed wing-tip. Wing-shape thus appears long and narrow, with swept-back, rather tern-like posture. Legs of Leach's are short and do not project beyond tail in travelling flight.

FLIGHT Travellingflight: Buoyant and graceful, wings rising and falling in deep tern-like beats. Course irregular, disrupted by vertical

IDENTIFICATION SUMMARY Leach's most closely resembles Madciran Petrel in its long angular wings and forked tail. It differs from that species in rather narrower width of wing and more

6 7 . Leach 's Petrel Oceanodroma leucorhoa, Bermuda, May 1976 (Keith Pellow)

leaping, bounding and sudden changes of speed and direction, interspersed with shear ing glides on bowed, slightly raised wings, and carpal joint raised a little higher than rest of wing.

Feeding flight: Wings stationary and raised slightly over back (up to 20°), but more usually just above the horizontal, with carpal joint raised higher than rest of wing, slowly inching Ibrwards into wind using feet as stabilisers, pat tering and splashing across surface, occasionally walking. Some litera­ture notes Leach's as rarely foot-pattering or walking, but , in gales at least, frequently does so, hanging motionless against the wind, short legs extended and treading water lor up to 30 seconds.

172 Identification of white-rumped petrels

pointed wing-tip. Compared with Madeiran , Leach's Petrel shows a more pronounced paler upperwing bar , but a less distinct and differently shaped white rump, which has the least side extension of any North Atlantic petrel. In travelling flight, Madeiran differs from Leach's in faster, shallower wing-beats, with rather longer, shearwater-like glides, the wings held flatter, often below the horizontal , working a steady zig-zag course, banking first to right and then to left wi thout vertical bounding or leaping. When feeding, Madeiran holds wings flatter, not raised at the carpal joint and usually more horizontal.

Wilson's Petrel differs from Leach's in shorter, more rounded wing-shape, which lacks the tern-like bend at the carpal joint; a shorter, broader upperwing bar; and a conspicuous white r u m p , which is seemingly always in view, whatever the angle of observation. The travelling flight of Wilson's is more direct than that of Leach's, and utilises faster, shallower wing-beats and shorter glides; its foot-pattering feeding flight, with wings raised high over its back, is very different from that of Leach 's .

Storm Petrel differs from Leach's in much shorter, more rounded wing-shape, square tail, and darker , virtually black plumage, with little if any upperwing bar, and a differently shaped, more extensive and more apparent white rump. The underwing has a diagnostic white stripe. T h e travelling flight of Storm Petrel is weaker than that of Leach's, utilising faster, fluttering wing-beats and shorter glides; Storm Petrel's wings are held higher over back when feeding.

Madeiran Petrel Oceanodroma castro SIZE Length 19-21 cm; wingspan 44-46cm. At sea, appears slightly smaller than Leach's, bu t averaging larger than either Storm or Wilson's .

PLUMAGE Madei ran Petrel appears mostly sooty-brown, paler than either Storm or Wilson's Petrels. Rump and uppertail-coverts white, extending to lateral undertail-coverts. This extension is slightly greater than that of Leach's , less than on either Wilson's or Storm. Black tips to longer white uppertail-coverts are rarely, if ever, seen at sea; thus, r u m p appears as conspicuous, even band across base of tail, quite distinct from duller V-shaped r u m p of Leach's . In this respect, Madei ran more closely resembles Storm Petrel. Madei ran has obscure pale brownish bar across upperwing-coverts, less pronounced than on either Wilson's or Leach 's , but more pronounced than on

6 8 . Made i ran Petrel Oceanodroma castro, Galapagos Islands, August 1982 {Peter Harrison

Storm. Whi te r u m p visible at ranges when upperwing bar is not; in the case of Leach's, reverse is true.

WING-SHAPF. AND JIZZ Some recent literature s ta tements are contradictory concerning relative length and shape of Madeiran's wings at sea. Brown (1980) described Madei ran as a 'relatively short winged petrel ' whilst in C r a m p & Simmons (1977) Made i ran is credited with 'long wings'. These seemingly contradictory statements arise because Madeiran has a wing-shape in termediate between those of Leach's and Wilson's . Wings are relatively long, usually with definite bend at carpal joint, but. because they are rather broader than Leach 's , with a blunt or rounded tip, they often appea r short. During glides, with wings outs t re tched, wing may appear to lack a noticeable angle (see LeGrand 1983). Thus,

Identification of white-rumpedpetrels 173

wing of Madeiran can be described as like that of Leach's, but rather broader and slightly shorter, with blunt wing-tip, or equally as resembling Wilson's, but slightly longer, usually with definite bend at carpal joint. Pale upperwing bar much less con­spicuous than on either of those species. At close range, under optimum conditions, tail of Madeiran is only slightly forked; the short legs do not project bevond tail in travelling flight.

Madeiran Petrels appear timid at sea: in my experience, they show no interest in following in the wake of vessels; they often fly off at a vessel's approach, and I have never been able to 'chum' them up from a small boat. They appear to spend more time sitting on the water than do the other three species.

FLIGHT Travelling flight: Steady and buoyant, weaving regular horizontal zig-zag of even height, with shallow wing-beats rising and

falling at quicker rate than Leach's, inter­spersed with shearing glides on wings held flat or bowed below horizontal. Unlike Leach's, wings are held flatter at carpal joint, and flight lacks that species' sudden changes of speed, height and direction. Occasionally, however (perhaps linked with prey sight­ings), doubles back on its course, gaining height, circling up to 3-4m above waves, at which times wings are raised higher, more tern-like, and flight becomes more erratic. In winds above force 5, flight often more direct, less zig-zagging, utilising fewer beats, shearing waves on stiff flat wings, banking and twisting over wave crests like small shearwater. Some observers describe the travelling flight as having a quality recalling Black Tern Chlidonias niger.

Feedingflight: Much like Leach's, but wings held flatter and closer to horizontal during foot-pattering; occasionally runs or hops across surface on stiff, outstretched wings.

IDENTIFICATION SUMMARY At sea, Madeiran appears intermediate between Leach's and Wilson's Petrels, the wings appearing broad but usually held forward and bent at the carpal joint with a slightly rounded tip. Differs from Leach's in broader, slightly more rounded wing-shape, less apparent upperwing bar, more conspicuous and even white band across rump (not dull and V-shaped) and lack of obvious fork to tail (usually appears square-tailed at sea, but under optimum conditions, 200m or less, slight fork to tail sometimes visible). The flight of Madeiran differs from that of Leach's in having a pronounced zig-zag progression, with faster, shallower wing-beats, with wings held flatter, more horizontal, during glides.

Wilson's Petrel differs from Madeiran in its shorter wings, which lack a definite bend at the carpal joint, a more apparent upperwing bar, greater side extension to white rump, and long legs, which project beyond tail in travelling flight. Feeding flight of Wilson's, with wings raised high over back and legs trailing, is distinctly different from that of Madeiran Petrel.

Storm Petrel is smaller, darker, with little if any upperwing bar, a diagnostic white stripe on underwing, and a weaker, more fluttering flight.

Acknowledgments The following people offered helpful advice and suggestions for improvements on a draft of this paper; Ron Naveen, Roy Phillips, Ian Sinclair and Victor Tucker. Photographs were made available by Alan Brady, Commander Chris Furze, David Hunt and Keith Pellow.

Summary The four North Atlantic white-rumped petrels (Wilson's Petrel Oceanites oceanicus, Leach's Petrel Oceanodroma leucorhoa, Storm Petrel Hydmbates pclagicus and Madeiran Petrel Oceanodroma castro) have diagnostic differences in structure and plumage which, under optimum conditions, should enable experienced observers to reach a positive field identification. These differences, together with flight characters, are discussed in detail, following a brief introduction on basic identification techniques.

References This list includes a number of useful sources of information not referred to in the text of this paper.

AINLEY, D. G. 1980. Geographic variation in Leach's Storm-petrel. Auk 97:837-853. ALLEN, R. G. 1962. The Madeiran Storm-petrel. Ibis 103b: 274-295. ATKIN, K. 1979. Flight characters of Leach's Petrel. Brit. Birds 72: 334-335. BAILEY, B. S., POCKUNGTON, R., & WILLIS, P. R. 1968. Storm-petrels in the Indian Ocean. Ibis

110:27-34.

174 Identification of white-rumpedpetrels

BOSWALL, J . 1979. Flight characters of Wilson's Petrel. Brit. Birds 72: 330-334. BROWN, R. G. B. 1979. Seabirds of the Senegal Upwelling and adjacent waters. Ibis 121:

283-292. 1980. Flight characteristics of Madeiran Petrel. Brit. Birds 73: 263-264.

CRAMP, S., & SIMMONS, K. E. L. (Eds).1977. The Birds of the Western Palearctic. vol 1. Oxford. CROSSIN, R. S. 1974. The storm-petrels (Hydrobatidae). Smithsonian Contrib. Zool. 158: 154-205. FINCH, D. W., RUSSELL, W. C , & THOMPSON, E. C. 1978. Pelagic birds in the Gulf of Maine.

Amer. Birds 3'2 {'2): 140-155. HARRISON, P. 1983. Seabirds: an identification guide. London. LEGRAND, H. E. 1983. Continental survey. Amer. Birds 36: 840. MARSH, P. 1980. Identification problem produced bv Leach's Petrel in moult. Brit. Birds 73:

474. MURPHY, R. C. 1936. Oceanic Birds of South America. Amer. Mus. Nat. Hist., New York. NAVEEN, R. 1981, 1982. Storm-petrels of the World: an introductory guide to their

identification. Birding 13:216-239; 14: 10-15,56-62, 140-147. RABBITTS, B., PAGE, D., & GREAVES, P. 1979. Leach's Petrels foot-pattering on water. Brit.

Birds. 72: 334. TUCKER, V. R. 1981. Wilson's Petrel in Cornwall. Brit. Birds 74: 299-301.

Peter Harrison, Trevescan Farm House, Trevescan, Sennen, Cornwall