Sora Rail in Stilly and the Identification of Immature Small Crakes D
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Sora Rail in Stilly and the identification of immature small crakes D. I. M. Wallace The immature Sora Rail Porzana Carolina present on St Agnes, Isles of Scilly, from 26th September to 9th October 1973 (Brit. Birds, 67: 320; Scilly Bird Report for IQ73'- 19-21) was the first to be recorded in Europe since 1920. The record was accepted by both the Rarities Committee and the Records Committee of the British Ornithologists' Union, and the species was once again listed in category A of the British and Irish list (Ibis, 116: 578). This short paper, which stems from the decision to publish in this journal the details of records that result in category promotion, also includes some comparative notes on immature small crake identification. DETAILS OF THE SORA RAIL IN SCILLY The bird was first seen in the rushes of the Big Pool by D. Smallshire, but early opinions on its identity were hopelessly divided. DS, A. R. Dean and B. R. Dean persisted in seeing slight but distinct differences from the closely related Spotted Crake P. porzana, the species to which others ascribed the bird on the basis of its noticeably buff under tail. The literature available at the time implied that this was a character only of the Spotted Crake and the controversy might have remained unresolved but for the arrival of fresh, open- minded observers, some already familiar with Sora Rails. A phone call from DS to DIMW on 7th produced redoubled efforts at identification. Close attention had already been paid to the bird by B. D. Harding on that date, and many other observers, notably D. S. Flumm, H. P. K. Robinson and M. J. Rogers, watched for it on 8th and 9th. By concentrating binoculars and mounted tele scopes on several patches of open mud over which the crake regularly strayed, uninterrupted views at ranges down to 15 metres and totalling 45 minutes were achieved. The following description summarises four separate sets of field notes: Size between Water Rail Rallus aquaticus and Little Crake Porzana parva (both alongside the Sora on 9th); close to Spotted Crake, but with longer tail, per haps more bulk or rotundity head-on, with longer and deeper bill. Bill greenish or brownish ochre, with distinct yellow surround to base; eyes dull brown; legs and feet dull ochraceous-green. Head strongly marked: crown rufous with noticeable black central stripe, forming striking pattern head-on; superciliary area buffy-grey, short streak over and behind eye bright white (very conspicuous at close range); ear-coverts greyish with faint, blackish stripe to rear of eye (drooping at the end) and obvious patches between eye and base of bill, fully black on right, but speckled grey on left. Throat whitish [Brit. Birds, 6g: 443-447, November 1976] 443 444 Sora Rail and small crakes with narrow black 'furrow' in centre, ending in tiny black bib (above neck crease). Nape greyish-brown; back strikingly patterned with at least four lines of distinctly marked feathers, each brown with blackish centre and white fringes, forming obvious lines head-on, and the rear four or five speckled white; rump blackish-grey; uppertail-coverts brownish-grey. Wing-coverts dull, 'oily' tawny, forming uniform patch in mid-body, with only inner greater coverts speckled white and fringed black; flight-feathers dark brown. Chest sides greyish, with lines of grey and buff mottling; front flanks greyish- buff with white spots, rear flanks deeply barred with dull black, grey and white with top edge white and some general buff mottling. Vent brown, flecked whitish; undertail-coverts warm buff, fading on longest to plain buffy white. Almost white under tail end (visible when flicked in alarm). At distance, in dull light, looked very similar to Spotted Crake, but, in good light, appeared noticeably paler on foreparts. Character also different, showing more neck and often standing up like Water Rail; movements on ground easy (with noticeable 'dread runs' to cover); flight apparently stronger than most small crakes. Quite tame and not shy, feeding on open mud for up to four minutes. Silent. Comparing these details with the description in Witherby et al. (1941), all the observers involved in a particularly concentrated watch on 8th October concluded that the bird was an immature Sora Rail in moult to first-winter plumage and that the apparent discrepancy of the undertail colour was unimportant. Opponents of the earlier claims became converted on the following day, and both review committees accepted the record without query. IMMATURE SMALL CRAKE IDENTIFICATION Given hindsight, it is clear that the controversy over the St Agnes Sora Rail owed most to the dangerous compression of field guide texts, in which the few lines simply lacked the detail necessary for correct identification; one plate (Robbins et al. 1966) contained a totally misleading illustration of a young Sora Rail. The rest of this paper is, therefore, devoted to specifying the crucial charac ters in the field identification of immature small crakes. It is written in the hope that fewer seconds (and most glimpses of small crakes are so timed) will be wasted in future. It is usual to group the four small crakes into two pairs, the Spotted Table 1. Measurements in mm of Spotted Crake Porzana porztma, Sora Rail P. Carolina, little Crake P. parva and Baillon's Crake P. pusilla (after Witherby et al. 1941 and American/Canadian literature) Total Wing («J?) Tail (<J) Tarsus (<J) Bill (&) length Spotted 109-125 43-49 30-37 16-21 230 Sora 98-117 46-53 30-38 18-22 215 Little 95-uo 50-57 28-32 i6-"i9 190 Baillon's 83-95 38-46 27-29 15-18 180 Sora Rail and small crakes 445 Fig. 1. Important characters of small crakes in immature plumage. Top right, Spotted Porzana porzana with red base to upper mandible, fully spotted chest, complete flank barring and white flecks on wing-coverts. Top left, Sora Rail P. Carolina with heavy yellow bill, strong crown pattern, white throat (with black division in first winter), mainly buff chest, rear flank barring and virtually uniform wing-coverts. Centre, Little P. parva with lightly barred flanks, virtually uniform wing-coverts and long wing point. Bottom, Baillon's P. pusilla with completely and heavily barred flanks, white flecks on wing-coverts and short wing point. All plumages as in early October Crake with the Sora Rail and the Little Crake with the Baillon's Crake P. pusilla, and to stress that the latter pair are much smaller. The true size order is demonstrated in table 1. The marked overlap of wing and tail lengths in the first three species should be noted; it is only Baillon's that is really a 'tiny runner' (though all four and also the ubiquitous Water Rail can appear to be so). Other struc tural differences are the long wing point and tail of the Little com pared with the Baillon's Crake's short wing point and tail, and the heavy bill of the Sora. 44-6 Sora Rail and small crakes Table 2. The diagnostic plumage characters of immature Spotted Crake Porzana porzana, Sora Rail P. Carolina, Little Crake P. parva and Baillon's Crake P. pusilla BAILLON S Crown Greyish-brown Chestnut, with with darker black centre mottling Lores First winter: increasingly mottled black Rear Bright white eye-brow Face Pale grey Buiry-grey Buffy-white Rich buff Throat Pale grey, with Immature: white un darker streaks marked ; first winter: white with black dividing line (diffi cult to see) Wing- Greenish-brown, Uniform tawny-brown, Uniform olive-brown, Warm brown, with coverts with many white with one line of with one line of several lines of decks white flecks white flecks obvious white flecks Back Olive brown Rufous-brown i Underparts Brown, grey and white, Pale buff and white, Pale buff and with many white spots with few white spots cream with faint over whole chest and on greyer chest motded lines and h strong barring over sides and obvious dusky bars on rear all Hanks barring only on rear flanks flanks Undertai! Buff Warm to pale buff, with longest feathers white (most obvious from behind) Outer edge White (edge of of wing bastard wing and outer web of first primary) Bill Yellowish-green, Wholly greenish- Wholly greyish- Wholly greyish- with orange or red yellow green, or with green base to upper orange base to mandible upper mandible Legs Glive-green Green Green Dull flesh, tinged grey or yellow Overlaps also occur in the plumage characters of the four species, but table a isolates the diagnostic marks, which are also shown in fig. i. The successful identification of an immature small crake rests mainly on the precise observation of size, structure, bill colour, wing-covert markings and underpart patterns, ACKNOWLEDGEMENTS I am grateful to A. R. Dean and the members of the Rarities Committee for their comments on an early draft of this paper. SUMMARY The identification of the first Sora Rail Porzana Carolina to be recorded in Europe for 53 years was initially made difficult by reference to inadequate literature, which implied that its undertail should have appeared white when, in fact, its colour is very similar to that of the Spotted Crake P. porzana. To prevent future confusion, a detailed description is given of the bird in question. This is followed by brief comparisons of the sizes and diagnostic characters of these and the other two small $ora Rail and small crakes 447 crakes, Little P. parva and Baillon's P. pusilla, in immature plumages, Witherby et al. (1941) remains a fully adequate reference for observers troubled with small crakes; its detailed plumage descriptions are unsurpassed.