Notes Identification of adult Sooty and Bridled Terns During a trip to St Lucia in the Caribbean in June 1986, I was able to watch both adult Sooty Sterna fuscata and adult Bridled Terns S. anaethetus and to study their identification.

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525 526 Notes

Fig. 1. Head patterns of adult Sooty Sterna Juscata (upper) and Bridled Terns S. anaelhetus. Note position at which bridle meets bill

Although Bridled may overlap in size with Common Tern S. hirundo, it certainly appears larger than that species in the field. It is described as somewhat smaller than Sooty, but in mixed flocks size difference is difficult to perceive. Bridled has a slighter build, slimmer wings and a more elegant and buoyant flight, in contrast to Sooty's more robust, heavy character; as both have the same tail measurements, the tail of Bridled is proportionately longer than that of Sooty. The extent of white from the forehead to above or beyond the eye, and the presence or otherwise of a neck collar are commonly given as fieldmarks. The exact position of the eye, however, is often difficult to see; I would suggest that emphasis should be on the extent of white on the forehead and loral regions and on the exact position of the black 'bridle'. On Bridled, the white is confined to a thin bar across the forehead extending over and beyond the eye, and the bridle runs across the full length of the maxillary feathering. On Sooty, the white forehead extends farther up towards the crown, but does not reach around beyond the eye; the bridle starts at the eye, but cuts down across the lores to join the bill around the gape. Thus, the area of white above the bridle is much deeper but less elongated on Sooty than on Bridled. The Bridled Tern's black cap stops abruptly at the lower nape; at this point the upper mantle is mid-grey (not white) and almost immediately merges into the dark slate of the mantle proper. The white of the rear ear-coverts runs up behind the cap, but the two sides do not quite meet; there is, therefore, only the suggestion of a pale collar, and this rather indistinct even at close range. In strong sunlight, the crown can appear grey and the collar is lost altogether. In some conditions, the pinch of white at the hindneck on flying Bridled can be useful, making a sharp white triangle on the side of the head, whereas on Sooty the black of the

271-274. Adult Sooty Sterna Juscata (top two) and Bridled Terns S. anaethetus (bottom two), St Lucia, June 1986 (Alan Harris) Notes 527 528 Notes Notes 529

Fig. 2. Adult Bridled Sterna anaethetus (left) and Sooty Terns S.fuscata in flight. Note slighter appearance of Bridled, with proportionately longer tail, also head and ear-covert pattern and primary pattern crown runs down the nape and joins the black mantle in a thin black strip. (Some field guides show a black half-collar on Sooty Tern: this is incorrect.) In flight, Sooty Tern appears black above and contrastingly white below. Its upperparts are black from crown to tail, without change in tone, and the tail has white only on the outermost feather. The inner wing shows a white leading edge identical to that of Bridled. Bridled Tern shows a typical tern cap and the diffuse grey collar quickly gives way to a dark slate-grey mantle, back and wings, the latter darkening towards the tips. On Bridled of the. race melanoptera (Caribbean, West Africa), the back gets progressively lighter towards the tail, the outer three feathers of which have white outer webs^ (thus showing more white than Sooty, on which only the outermost tail feather shows white); Bridled Terns from the Red Sea and Persian Gulf (race fuligula), however, show a similar tail pattern to Sooty, and more uniform dark upperparts. It is important to note that in bright conditions Sooty Terns can look very pale above, thus resembling Bridled. At such times, I noted Sooty as showing a tawny tinge, whereas Bridled (of race melanoptera at least) still remained slaty, in contradiction to most of the literature. From below and at a distance, adult Sooty and Bridled Terns are difficult to separate. In dull conditions, the extent of white on the under

275-277. Adult Bridled Sterna anaethetus (top one) and Sooty Terns S.juscata (bottom two), St Lucia, June 1986 (Alan Harris) 530 Notes primaries is a most useful feature, as noted by Stefan Lithner (Brit. Birds 76: 348-349). Basically, both species have primaries and secondaries a light grey, darkening noticeably towards the extremities. The rest of the underwing—the coverts—is white. Bridled has white inner webs to the outermost three primaries, producing a white 'finger? down the middle of the outer wing, fading towards the tip. This is a good feature at moderate distances in dull conditions, and excellent on individuals overhead; but any strong sunlight 'burns out' the greyness of Sooty Tern, particularly when banking away, so care is needed. ALAN HARRIS 117 Spring Hills, Harlow, Essex CM20 IT A

Behaviour of Swifts at House Martin colony A previous note (Brit. Birds 79: 339) on a Pallid Swift Apus pallida occupying the nest of a House Martin Delichon urbica recalled the following observations. A House Martin colony at Slinfold, West Sussex, comprising between two and four natural nests and seven nestboxes, has been watched since 1968; Swifts A. apus made annual visits to the colony from 1974 until 1977. Visits started soon after the Swifts had returned to the area, and continued throughout the breeding season. These normally involved several high-speed flights with two to four Swifts flying past very close to the House Martin nests, with one sometimes banging a nest with its wing. The number of visits varied between both days and times of the day, although most were in the morning or late evening. For example, on 6th July 1976, two Swifts made 22 visits between 06.30 and 13.00 GMT, and eight more visits between 19.05 and 21.40 GMT. Occasionally, a swift left the party to circle slowly nearby, prior to hovering in front of a nest. More rarely, one landed on a nest, staying briefly (5-15 seconds), though on no occasion did one actually enter a martins' nest. Visits by smaller parties usually took place in silence. In contrast, towards the end of July, parties of 12-15 Swifts made very noisy evening visits. Adult House Martins reacted as follows: early in the season, they left their nests in alarm, but, while incubating, they hissed vigorously at lone Swifts hovering or landing on a nest, leaving only when the threat had subsided. Well-grown young martins crowded the nest entrances hoping to be fed, but martins of all ages were intimidated by the larger, screaming Swift parties, and crouched low in the nest. Once, a Swift tried unsuccessfully to pull an adult House Martin from a nest by its forewing, but nestlings were never attacked. The Handbook recorded Swifts nesting in old House Martin nests, and Walpole-Bond (1938, History of Sussex Birds) mentioned Swifts roosting in such sites, but there is no mention of either activity in BWP vol. 4. S. W. M. HUGHES 6 West Way, Slinfold, Horsham, West Sussex RH13 7SB

Isabelline Wheatear using 'canopy technique' when feeding On 31st October 1986, while I was watching individuals of six species of wheatear Oenanthe on one small dry-soil field at Elot, near Eilat, Israel, the feeding Notes 531 behaviour of one Isabelline Wheatear O. isabellina attracted particular attention. It stood on slightly raised mounds, stones or lumps of dry earth, apparently looking for food, then rapidly hopped or flew 3-6 m. It then either picked up a food item instantly or, more often, opened its wings wide, to the side and forwards in front of its head (in a fashion recalling film that I have seen of Black Heron Egretta ardesiaca producing a shade-canopy with its wings when feeding in water); the leading edges of the wings did not touch in front of the head, but left a small gap, the effect nevertheless being to shade the area where the wheatear then apparently always found a food item. The wheatear then flew a short distance to another lookout perch before repeating the process. I interpreted this behaviour as a method by which the wheatear provoked its potential prey—spotted from a distance, but currently hidden—into tell-tale movement. This very distinctive feeding technique was employed by this Isabelline Wheatear five times during one 20-minute spell when I watched it closely. I do not recall ever before having seen a passerine behaving in this way. J. T. R. SHARROCK Fountains, Park Lane, Blunham, Bedford MK44 3NJ

Probable hybrid Willow X Greenish Warbler On 8th June 1986, whilst birdwatching in a wood composed mainly of silver birch Betula pendula in Highland Region, I located a singing warbler which immediately struck me as something unfamiliar. My initial identification was a Greenish Warbler Phylloscopus trochiloides, as I had heard one a few years ago in a Highland glen and the song was similar. I called to R. Shand and S. Rivers, and we observed the bird for about an hour. The song varied from a Willow Warbler P. trochilus downscale cascade ending in 'scratchy' notes to a phrase of pure 'scratchy' gabble, the latter resembling the previously heard Greenish Warbler. The bird sang continuously throughout the time we watched it, and the following description was taken: VJPPERPARTS Head, mantle and rump olive- UNDERPAETS Chin, throat and belly off-white brown with faint yellow tinge; indistinct pale with yellow tinge; greyish upper breast, yellowish supercilium extending to ear- Undertail-coverts not seen, coverts; darkish eyestripe. Wing-coverts BARE PARTS Bill brownish with pale orange ohve-brown, no trace of a wing-bar; base to lower mandible; eye dark; legs primaries and rectrices brown. pinkish-brown; soles of feet yellow ochre. We contacted Roy H. Dennis and returned to the area about an hour later. The bird was located immediately and after a short while R. H. Dennis concluded that the bird had the plumage and jizz characteristics of a hybrid between Willow and Greenish Warbler. He commented that the song was variable, sometimes having a stronger Willow Warbler character and at other times being more like Greenish Warbler. DOUGLAS E. DICKSON 133 Duddingston Drive, Kirkcaldy, FifeKY26XG

Carrion Crow picking up dead fish with its feet The taking of fish by opportunistic Carrion Crows Corvus corone has been reported by several observers, and in some detail by P.J. Dunn (Brit. Birds 78: 151-152), but all the observations appear to concern crows capturing fish with the 532 Notes bill, as is to be expected (Dr C.J. F. Coombs in litt). On 23rd June 1984, at Rostherne Mere NNR, Cheshire, Malcolm Greenhalgh and I watched a Carrion Crow take a dead fish, which we identified through binoculars as a roach Rutilus rutilus, from the calm surface of the mere. The crow gripped the fish with its feet, and carried it in the manner of an Osprey Pandionhaliaetus. MALCOLM C ALVERT 12 Hill Drive, Handforth, Wilmslow, Cheshire SK9 3AR