69 AUSTRALIAN FIELD ORNITHOLOGY 2003, 20, 69-76

Jouanin's Petrel Bulweria fa/lax in Australia

MIKE CARTER,

Summary

30 Canadian Bay Road, Mount Eliza, Victoria 3930 (Email: pterodroma@bigpond.com)

A record of two Jouanin's Petrels Bulweria fallax seen over continental slope waters south­west of Ashmore Reef on 15 October 2000 has been accepted by the Birds Australia Rarities Committee. This paper documents the occurrence, which is the first record for Australia, refers to other potential sightings and discusses identification criteria.

Introduction

Between 1996 and 2001, there were six expeditions to research the pelagic birds occurring at the confluence of the Timor Sea and the Indian Ocean off the northern coast of Western Australia. The author participated in all but one, each of which was of seven or eight days' duration, Broome to Broome, aboard the 22-m-long ketch Jodi Anne 2. All were in the period from early October to early November. On the first of these expeditions, a bird suspected of being a Jouanin's Petrel Bulweria fallax was seen. During expeditions in 2000 and 2001, Jouanin's Petrels were suspected or 'reported' on at least eight occasions. Whilst submissions on other sightings are in preparation or currently being appraised by the Birds Australia Rarities Committee (BARC), a sighting of two birds together during the cruise in October 2000 has been accepted, case number 349 (Tony Palliser in litt. 3 February 2003). This confirms the presence of the species in these waters.

The participants on this cruise were the organisers Tony Palliser and George Swann, along with David Andrew, Rohan Clarke, David James, Mike Hunter, Penny Hunter, Peter Lansley, Roger McGovern, Jo Wieneke and myself.

The sighting

About one hour before midday on 15 October 2000, our vessel approached two dark petrels sitting together on the sea. Our location was l2°41'S, 122°37'E, some 68 km south-west of Ashmore Reef. We were sailing on a 28° course at a speed of about 8 knots. From a chart, the water depth was estimated at 1275 m but one hour later it had reduced to 600 m as we crossed the continental slope on our approach to the Reef.

The general appearance and posture of the birds were similar to those of the frequently observed Bulwer's Petrel B. bulwerii but the birds appeared bigger­headed and larger than that species. When we were about 100 m from them they took flight. As they rose and turned in an upward loop, their long tapered tails, stepped at mid-length, were revealed. The birds flew towards us, passed parallel to the boat close enough (from 50-70 m) to provide excellent views, and disappeared astern. The weather was fine, sunny, hot and humid, with 50% cloud cover. There was virtually no wind and the sea was calm on a zero swell. The birds were well illuminated as the sun was above and behind us. The duration of observation was about one minute.

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We were certain that both birds were Jouanin's Petrels and this engendered confidence regarding previous sightings.

Description

The birds were very dark, almost black, all over, including the bill, except for a paler, brownish, partial covert-bar on the upperwing. This was sometimes, but not always, visible in flight. Because it was fainter, narrower, did not reach the innerwing and stopped well short of the carpal joint, it was less extensive and more obscure than the covert-bar displayed by Bulwer's Petrel. There was no scalloping caused by pale fringes to the feathers such as is usually present on the much browner Wedge-tailed Shearwater Puffinus pacificus.

In shape, the birds resembled Bulwer's Petrel, except that the tapered tail was longer and broader, less evenly graduated, and, instead of terminating in a point, was almost square, just slightly rounded at the tip. The width of the tail at the tip was about half that at its base. The outer rectrices extended only half the full length of the tail, creating an abrupt step in the outline. This was symmetrical and evident in both birds but seemed to be more prominent in the nearer bird. The step was not visible in direct flight, only during take-off. The wings were long and pointed, proportionately narrower at the base than those of Bulwer's Petrel (which seems to be 'all wings'). The head and bill appeared large and heavy and the forehead was very steep. The Pterodroma-shaped bill was long and robust and proportionately at least as large as that of the Great-winged PetrelPterodroma macroptera gouldi. Tony Palliser likened it to that of the much larger Tahiti Petrel Pseudobulweria rostrata, a fairly common bird in this area.

Although the birds' flight was somewhat similar to that of Bulwer's Petrel, it was more languid, approaching that of the Wedge-tailed Shearwater. They flew slightly higher above the surface than a typical Bulwer's Petrel on a calm day, but this might have been due to the fact that they were larger birds. Most of the time, the bill was inclined downwards, not vertically like a tern fishing, but at about 45°. At times, the head was lifted so that the crown was raised above the line of the back.

No other birds were directly available for size comparison, but these birds were considerably smaller than a Wedge-tailed Shearwater (seven seen previously, nine during this voyage), one of which was seen soon after this observation, thus assisting determination of size. They were judged to be noticeably larger than most of the other, more frequently observed, all-dark petrels encountered on this expedition: those positively identified in descending order of size were Bulwer's Petrel (35 seen in the two previous days, 65 on the voyage), Matsudaira's Storm­Petrel Oceanodroma matsudairae (13, 55), and Swinhoe's Storm-Petrel 0. monorhis (24, 32).

Identification

The description above clearly identifies these birds as Jouanin's Petrels. Given that they were wholly dark, almost black birds, the diagnostic features leading to this conclusion, ranked in a putative order of significance, are: (1) the robust bill inclined downwards in flight; (2) the long, stepped, rather substantial, tapered, almost square-tipped rather than pointed tail; (3) the absence of a bold pale covert -bar; and ( 4) the birds' medium size. Each of these characters is dealt with separately below. The combination of these features distinguishes the birds from

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all other dark-plumaged species of family Procellariidae, in particular the two species most likely to be confused- Bulwer's Petrel and Wedge-tailed Shearwater (Enticott & Tipling 1997).

Mass and carriage of the bill

Jouanin's Petrel has a heavy, robust bill. Bulwer's bill is similar in shape but is shorter, narrower and not as deep. Using the diagrams in Warham (1990: p. 133) I calculate that the bill of Jouanin's has an area in profile twice that of Bulwer's Petrel. If, as photographs suggest, Jouanin's bill is proportionately wider, its volume will be nearly three times that of Bulwer's Petrel. In suitable conditions, this difference is easily detected at ranges of well over 200 m. Other all-dark procellariids that have a substantial bill, for instance Mascarene Petrel Pterodroma aterrima and Fiji Petrel P macgillivrayi, have a shorter, differently shaped, tail. The Wedge-tailed Shearwater has a long, slender bill (Harrison 1983, 1987; Marchant & Higgins 1990; Enticott & Tipling 1997; Beaman & Madge 1998). Close-up photographs showing the heavy bill of Jouanin's Petrel are shown by Bourne (1960), Seto et al. (1996) and Taleb (2002). The bill of a Bulwer's Petrel is well shown in a photograph in Kirihara et al. (2000).

The downward inclination of the bill in flight has been noted by a number of observers and is said to be distinctive (Enticott & Tipling 1997, Beaman & Madge 1998). Richard Porter (in !itt. 18 January 2002), who knows the species well from the Arabian Sea, stated that the large black bill is obvious on birds sitting on the sea but is not easily seen in flight. More useful is the fact that the bill is always held at a 45° angle, unlike that of the all-dark shearwaters.

The long, tapered, comparatively substantial tail with 'step'

Only Bulwer's Petrel has a tail that is similar in shape, but the tail in that species is narrower, more attenuated and pointed at the tip. Richard Porter (in !itt. 18 January 2002) noted that the tail of Jouanin's Petrel is quite long but not obviously so, and that the graduation is difficult to see except at close range. Moreover, Bulwer's Petrel lacks the sudden step on the outer edge, the abrupt change in width present in the pair we saw. The Wedge-tailed Shearwater has a more fan-shaped, pointed tail, which also lacks the step. No other procellariid has a long, similarly shaped tail (Harrison 1987, Enticott & Tipling 1997, Beaman & Madge 1998).

Although the drawing in Harrison (1983) showed a Fiji (MacGillivray's) Petrel with a long pointed tail similar to that of Bulwer's Petrel, in a later work Harrison (1987) stated that the species has a short tail and drew it accordingly. This is confirmed by Enticott & Tipling (1997). Although the Mascarene Petrel, which is similar in overall length to Jouanin's Petrel, also has a relatively full tail, it is 20-30% shorter, has parallel sides and a square tip with rounded corners (Jouanin 1955, Enticott & Tipling 1997; John Darnell pers. comm.).

Contra Harrison (1987) and Enticott & Tipling (1997), in the opinion of most observers who saw the birds on this expedition, Bulwer's Petrel also has a relatively shorter 'tail-end'. That is, the proportion of the total length from the bill to the tip of the tail projecting behind the wings appears relatively shorter compared with the portion anterior to the wings. This is possibly due to the very broad base to the wings on Bulwer's Petrel, which appears to be 'all wings', rather bat-like. A study of the photographs in Harrison (1987), van den Berg et al.

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(1987), Seto et al. (1996), Enticott & Tipling (1997), Kanouchi et al. (1998), Legrand et al. (1999) and Kirihara et al. (2000) supports these statements. In the identification key of Harrison (1987: p. 306), Jouanin's Petrel is correctly drawn with a longer tail than Bulwer's Petrel but the difference is actually more outstanding because, in my opinion, the rear-end ofBulwer's is even shorter than drawn.

The step in the tail, first described in Harrison (1987), is now generally regarded as a diagnostic feature. For instance, Beaman & Madge (1998) described the step as 'characteristic' of the species.lt is visible in a photograph taken in July (Harrison 1987, van den Berget al. 1987, Enticott & Tipling 1997) and in three photographs taken in August (Harrison 1987, Seto et al. 1996, Taleb 2002). But the reliability and constancy of this character has been questioned. Richard Porter (in litt. 18 January 2002) said that he has never seen the stepped tail and guesses that it is only visible as the bird spreads its tail on take-off when flushed from the sea at close range. After seeing several Jouanin's Petrels in the Arabian Sea in June 1990, A.P. Benson (in Cheshire 1991) commented that 'the "stepped" tail mentioned by Harrison (1987) was not a good field mark, being seen only at close range and then only in a small proportion of birds'. Hirschfeld (1994), whilst conducting land-based observations, found that the step was only visible on birds within 400 m. Thus it is certainly a feature in at least some birds from June to August and our observation extends the envelope of occurrence to October. Danny Rogers (in Marchant & Higgins 1990) suggested that it might be an artefact of moult (see opposite). Since two of the above-mentioned birds with stepped tails were breeding or potentially breeding, this suggests that it may be normal in a percentage of the population rather than a transient feature, and may be related to age or sex; this assumes that breeding birds are unlikely to be in moult.

Just what produces the step is a mystery. In June 2002, at the British Museum's Natural History Department at Tring, England, Neil Cheshire (pers. comm.) compared six skins of Jouanin's Petrel with 16 of Bulwer's Petrel. He detected no significant difference in tail structure and nothing in the relative lengths of the rectrices of Jouanin's that might be construed as a step. At my request, he asked Clive Mann to measure the stagger of the rectrices; this was done for three Jouanin 's and two Bulwer's Petrels. As in the Bulwer's Petrel example given below, the graduation was erratic, exhibiting no regular pattern in either species and providing no evidence of an abrupt step. The Jouanin's Petrels had a tail length (that is the central feathers (tl)] of 123, 119 and 114 mm, with the outer feathers (t6) shorter by 59, 37 and 41 mm respectively. The Bulwer's Petrels had tails of 114 and 116 mm, with t6 shorter by 31 and 36 mm respectively.

Further evidence that the length of the outer tail-feather is not by itself the character that causes the step comes from a skin in the Singapore University collection. Originally labelled Mascarene (Reunion) Petrel, it was re-identified by John Darnell (in litt. 14 December 2001) as a Jouanin's Petrel. Darnell found no evidence of a step in the tail; indeed, it was a very evenly tapered tail. The five graduations from t1 to t6 were each between 8 and 10 mm, with t1 extending 46 mm beyond t6. Total tail length was 121 mm. This is consistent with dimensions given by Jouanin (1955), which for two specimens with tail lengths of 123 and 124 mm had t1 50 mm longer than t6.

1\ Bulwer's Petrel specimen in Museum Victoria, Melbourne, has the following graduations in mm (Rory O 'Brien in litt . 23 January 2001). Because of the asymmetry, each side was measured separately.

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Left side: t1 to t2 and t3, 12; to t4, 14; to t5, 7; to t6, 10. Thus t1 extended 43 mm beyond t6.

Right side: t1 to t2, 11; to t3, 11; to t4, 8; to t5, 8; to t6, 9. Thus t1 extended 47 mm beyond t6.

According to Marchant & Higgins (1990), in Bulwer's Petrel t1 extends 40 to 45 mm beyond t6, and the tail overall varies from 102 to 117 mm in length. In an extensive literature search, covering the references cited here, I found no reports of a 'step' in the tail of Bulwer's Petrel.

In four sightings of Jouanin's Petrels on 1 April 2000 in the western Indian Ocean (blocks 14° and 15° S, 53o E), John Darnell (in !itt. 14 December 2001) did not notice a step in the tail. However, in one of his excellent field sketches, that of a bird with the tail spread while banking, there is a hint of its presence.

Danny Rogers (pers. comm.) confirms that the statement under Recognition for Bulwer's Petrel, in Marchant & Higgins (1990: p. 557 ), viz. 'Harrison's (1987) observation that Bulwer's has short outer tail-feathers forming a "midway step" in the tail needs confirmation; possibly due to moult' is an editorial error. Harrison's observation actually refers to Jouanin's Petrel and Rogers' comment was intended to relate to the statement on that species.

To what extent, if any, the step in the tail of Jouanin's Petrel is a transient feature and what causes this appearance is unknown. It seems unlikely that it is an artefact of moult. Perhaps it is the width or relative shape of the outer rectrices or merely the way the tail is held. I could find no evidence to support the claim by Harrison (1987) that it is formed by very short outer tail-feathers or by an uneven stagger in the taper. That it exists as an occasional field character, however, is certain.

Since the condition is not reported in the comparatively well-known Bulwer's Petrel, we may conclude that a Bulweria petrel with an obvious step about mid­length in the outer tail is a Jouanin's Petrel.

Uniformly dark plumage except for faint, incomplete, covert-bar

Although Mascarene and Fiji Petrels are very dark, both are virtually uniform in colour above, lacking even the partial covert-bar present in the birds described here (Enticott & Tipling 1997).

Distant Bulwer's Petrels can also appear mostly black, but when viewed at close range in good light, as in this observation, they show a much paler, conspicuous covert-bar that extends forward to the carpal joint (Marchant & Higgins 1990, Beaman & Madge 1998). Whereas some Jouanin's Petrels in worn plumage show a pale band on the wing (Bourne 1960, van den Berg et al. 1991, Hirschfeld 1994, Enticott & Tipling 1997, Beaman & Madge 1998), this is never as long or as prominent as that in Bulwer's Petrel. Photographs showing the upperwings of both Jouanin's and Bulwer's Petrels are in Harrison (1987) and Enticott & Tipling (1997). Photographs of Jouanin's Petrel are shown by van den Berget al. (1987) and Seto et al. (1996), whereas Kanouchi et al. (1998), Legrand et al. (1999) and Kirihara et al. (2000) show photographs of Bulwer's Petrel. All the Bulwer's Petrels examined at Tring had a prominent pale covert-bar but none of the Jouanin's Petrels showed this feature (Neil Cheshire pers. comm.).

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The Wedge-tailed Shearwater never has a pale covert-bar, and its much browner plumage (Harrison 1987, Marchant & Higgins 1990) would be very evident in the conditions pertaining to this observation.

Medium size

Jouanin's Petrel i~ classified as a 'small to medium-sized' seabird, whereas Bulwer's Petrel is classified as 'small' and the Wedge-tailed Shearwater as 'large' (Enticott & Tipling 1997). From the dimensions given by Harrison (1987), I calculate that Bulwer's Petrel is about 5 em shorter in length and 12 em smaller in wingspan than Jouanin's Petrel. Wedge-tailed Shearwater averages 12 em longer and 22 em larger in wingspan. Calculations from dimensions given by Marchant & Higgins (1990) and Warham (1990) concur. Thus, Bulwer's Petrel is about 20% shorter, and Wedge-tailed Shearwater roughly 40% longer, than Jouanin's Petrel. Similarly, Bulwer's Petrel is about 20% smaller, and Wedge-tailed Shearwater around 20% greater in wingspan than Jouanin's Petrel. Using weights from Warham (1990) (Jouanin's Petrel c. 173 g, Bulwer's c. 97 g), and mean weights from Marchant & Higgins (1990) (Bulwer's Petrel 102 g, Wedge-tailed Shearwater c. 380 g), Bulwer's Petrel is about 75% lighter and Wedge-tailed Shearwater is about 220% heavier than Jouanin's Petrel.

Differences of this magnitude are easily detected, especially in calm conditions at close range, so our assessment that the birds were medium-sized can be assumed to be reasonably accurate. This size category includes Jouanin's Petrel and excludes most otherwise similar species including Fiji Petrel, which is similar in size to Bulwer's Petrel (Enticott & Tipling 1997). 1t does not, however, eliminate Mascarene Petrel.

Flight

Richard Porter (in !itt. 18 January 2002) described the flight of Jouanin's Petrel as rather languid with typically up to five leisurely wing-beats followed by a slightly banking glide on arched wings. In light winds or calm conditions, they fly fairly close to the sea with a mixture of wing-beats and long glides. In winds of force 3 and above, they may climb 2-5m in an arc above the waves. Beaman & Madge (1998) stated that in very calm conditions Jouanin's Petrels beat their wings continuously, recalling a jaeger Stercorarius sp. This characteristic was not noted in the birds described here, but was a feature of an earlier sighting currently under assessment by BARC.

Discussion

Van den Berget al. (1991) had 'hardly any difficulty distinguishing Jouanin's and Bulwer's Petrel' based on size and 'markedly different flight' . However, they did have problems differentiating between Jouanin's Petrel and Wedge-tailed Shearwater when distant. They found the long-winged appearance, dark colour, and heavy bill held slightly downwards the best characters for distinguishing Jouanin's Petrel. The slender bill of the Wedge-tailed Shearwater is 'held more horizontally'. It seems peculiar that the size difference between Wedge-tailed Shearwater and Jouanin's Petrel was less apparent than that between Bulwer's Petrel and Jouanin's Petrel, given that, as demonstrated above, it is actually considerably greater.

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It is interesting to note that although photographs taken during these observations show the stepped tail (van den Berg et al. 1987), this was not mentioned as a field character.

About Jouanin's Petrel

Jouanin's Petrel is one of the least known seabirds (Warham 1990). It was unknown until comparatively recent times, being first described by Jouanin (1955). The first nest was discovered on Socotra in the Arabian Sea as recently as August 2000 (Taleb 2002). Over 1000 have been seen in one evening streaming along the coast of that island (Taleb 2002). Since large numbers have also been seen off other Arabian Sea islands, the population is thought to be 'substantial' (Warham 1990). Its distribution at sea spans the northern Indian Ocean with the largest numbers occurring in the Arabian Sea. Vagrants have appeared in the Mediterranean Sea and twice in the Pacific Ocean. The two Pacific Ocean records were of birds that appeared in colonies of nesting Bonin Petrels Pterodroma hypoleuca in the north-western Hawaiian Islands. The first was on Lisianski Island in 1967 and the second was on Sand Island, Midway Atoll, in August and October 1993 (Seto et al. 1996). The occurrence of Jouanin's Petrels in the Pacific Ocean leads to conjecture as to their route from the Indian Ocean; it seems most likely that this would have been through tropical waters north of Australia.

During cruises across the northern Indian Ocean to and from Suez to the south-eastern tip of Sumatra, van den Berget al. (1991) recorded 753 Jouanin's Petrels. The most easterly and southerly noon position of the ship on these voyages was 6°14'S, 103°00'E. The nearest sighting of a Jouanin's Petrel to Australian waters was off the coast of Sumatra on 1 July 1984 at 5°20'S, 100°30'E (van den Berg et al. 1991). This is 2500 km north-north-west of our sighting. There are no previous accepted records of Jouanin's Petrels from Australasia.

Evidence suggests that Bulwer's Petrel is absent from breeding areas during the first two to three years of life and does not breed until about the fifth year (Warham 1990). It is known that some Bulwer's Petrels remain in their winter quarters throughout the year. It seems likely that Jouanin's Petrel may have a similar regime.

Acknowledgements

I thank those who shared this observation (named in the introduction) for their contributions, in particular Rohan Clarke and Peter Lansley for initially spotting the sitting birds. Tony Palliser and George Swann provided their field-sketches. David James and Peter Lansley provided typed transcriptions of their detailed field-notes. For their precise navigation, seamanship and providing for our every need whilst at sea, I also thank our skipper, Ron Kitcher, and his crew. For providing photocopies or drawing my attention to articles in the literature, I thank Neil Cheshire, Rohan Clarke, David Eades, Maarten Hulzebosch, David James, Peter Lansley, Danny Rogers and Tadao Shimba. Bill Rutherford and Adrian Boyle showed me the frozen specimen and provided measurements of the Bulwer's Petrel found alive at Broome in October 2000. Neil Cheshire and Clive Mann (U.K.) examined and reported on skins in the British Museum. Neil also sent photographs of a Jouanin's Petrel found in the scuppers of his ship while in the Arabian Sea. John Darnell sent detailed notes on the specimen in Singapore and on his observations in the western Indian Ocean. Rory O'Brien made detailed measurements of the tail of a Bulwer's Petrel specimen in Museum Victoria. Danny Rogers discussed and helped resolve problems I had analysing the literature and other data. Dick Newell (U.K.) made available several photographs of Jouanin's Petrel by placing them on his internet web site. Richard Porter (U.K.) shared with me his extensive expenence of this species at sea, provided photographs of the nesting bird long before this thrilling discovery was made

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public, and forwarded the text of Nadim Taleb's paper describing the event. Peter Crabtree read and corrected the draft. Ken Harris performed one of my regular census counts of birds of the Edithvale Wetlands, which gave me time to finish this paper.

References

Beaman, M. & Madge, S. (1998), The Handbook of Bird Identification for Europe and the Western Palearctic, P.rinceton University Press, Princeton, New Jersey.

Bourne, W.R.P. (1960), 'The petrels of the Indian Ocean', Sea Swallow 13, 26-39. Cheshire, N.G. (1991), 'Notes on seabird reports received in 1990', Sea Swallow 40, 25. Enticott, J. & T1pling, D. (1997), Photographic Handbook of the Seabirds of the World, New

Holland, London. Harrison, P. (1983), Seabirds: An Identification Guide, Croom Helm, Beckenham, Kent

(U.K.). Harrison, P. (1987), Seabirds of the World: A Photographic Guide, Christopher Helm, London. Hirschfeld, E . (1994), 'Observations of seabirds off Dhofar (Oman) 1990-2', Sandgrouse 14,

62- 71. Jouanin, C. (1955), 'Une nouvelle espece de procellariide', L'Oiseau et RFO 27, 12-27. Kanouchi, T, Abe, N. & Ueda, H. (1998), Wild Birds of Japan, Yama-Kei, Tokyo (in Japanese). Kirihara, M., Yamagata, N. & Yoshino, T (2000), Japanese Bird 550: Waterbirds, Bunichi

General Publisher, Tokyo (in Japanese). Legrand, H.E. jr., Guris, P. & Gustafson, M. (1999), 'Bulwer's Petrel off the North Carolina

coast', North A merican Birds 53, 113-115. Marchant, S. & Higgins, P.J. (Eds) (1990), Handbook of Australian, New Zealand & Antarctic

Birds, vol. 1, Oxford University Press, Melbourne. Seto, N.W.H., Warham, J., Lisowski, N.L. & Tanino, L. (1996), 'Jouanin's Petrel Bulweria

fa /lax observed on Sand Island, Midway Atoll', Colonial Waterbirds 19, 132-134. Taleb, N.M.A. (2002), 'The discovery of a breeding colony of Jouanin's Petrel Bulweria fa /lax

on Socotra, Yemen', Sandgrouse 24, 105-108. van den Berg, A.B., Hazevoet, K., van Ijzendoorn, E ., Moerbeek, D., Schekkerman, H. &

de Wijs, R. (Eds) (1987), 'Varia: Jouanin's Petrel', Dutch Birding 9, 72-73. van den Berg, A.B., Smeenk, C., Bosman, C.A.W., Haase, B.J.M., van derNiet, A.M. & Cadee,

G.C. (1991), 'Barau's Petrel Pterodroma baraui, Jouanin's Petrel Bulweria fa/lax and o ther seabirds in the Northern Indian Ocean in June- July 1984 & 1985', A rdea 79, 1-14.

Warham, J. (1990), The Petrels: Their Ecology and Breeding Systems, Academic Press, London .

Received 15 February 2003 •