Western Sandpiper
Calidris mauri (Cabanis, 1857)
Photo © By Alan D. Wilson - naturespicsonline.com ([1]), CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=3179192
STATUS
Nearctic. Monotypic.
OVERVIEW
Admitted nationally as the first for Britain (BOURC (1963), Ibis 105: 289), but since then proven to have been misidentified.
NOT PROVEN
0). 1956 Fair Isle Kirki Geo, 27th May to 3rd June, trapped 29th May.
(K. Williamson, Fair Isle Bird Observatory Report 1955/56: 21; P. E. Davis, Fair Isle Bird Observatory Bulletin 3: 111; K. Williamson & H. G. Alexander, British Birds 50: 350-351; K. Williamson & H. G. Alexander, Scottish Naturalist 69: 145-147; E. V. Baxter, Scottish Birds 1: 30; D. G. Andrew, Scottish Birds 2: 342; I. C. T. Nisbet, British Birds 56: 55-58; S. Marchant, British Birds 56: 382-383; I. C. T. Nisbet, British Birds 56: 383; BOURC (1963), Ibis 105: 289; Thom, 1986; M. Garner, British Birds 98: 356-364; A. D. Prowse, British Birds 99: 149-151).
[D. I. M. Wallace, C. Bradshaw & M. J. Rogers, British Birds 99: 463; BOURC (2006), Ibis 149: 194; BOURC (2007), Ibis 149: 652-654].
History K. Williamson & H. G. Alexander (1957) in British Birds, Vol. L. pp. 350-351, say: 'That there might be considerable difficulty in separating these two North American waders in the field did not occur to us until we found it necessary to make a decision in favour of one or the other with a small greyish wader at Fair Isle at the end of May 1956 (Williamson and Alexander, in press). This bird, first thought possibly to be a Baird's (Calidris bairdii), was in company with a group of Dunlins (C. alpina).
After watching for some time we provisionally identified it as either a Semipalmated (C. pusilla) or a Western Sandpiper (C. maurii) when it was seen through a telescope that the toes were partially webbed. Identification as the former was confirmed later by trapping. There are plumage-differences given for Baird's and Semi-palmated, but they appear to be slight, and plumage is notoriously difficult in waders when in change from winter to summer-dress and vice versa. Rowan (1926), Witherby et al. (1944) and others have discussed the difficulties: in both, the mantle-pattern could be described as "scaly" (Peterson, 1947), the wing- and tail-patterns are almost identical, and both have legs which appear to be black at short distance, but are in reality dark olive-green at close quarters.
In the case of the Fair Isle example we rejected Baird's because the bird was obviously smaller than a Dunlin, and we felt from a glance at the measurements given by Witherby (op. cit., pp. 238, 240, 268) that this ought not to be so (Baird's, male wing 116.5-127.5 mm., female 113-132mm.; Southern Dunlin schinzii, male 106-112mm., female 110-120mm.; Northern Dunlin alpina, male 111-116mm., female 111-117mm. with up to 122 mm. recorded). However, those who have recorded undoubted Baird's Sandpipers in this country in recent years have all stressed that their specimens were smaller than Dunlins (White, 1951; Fluke, 1953; Boyd, 1955). It would be highly dangerous, therefore, to attempt to discriminate between these two Americans on the basis of size-comparison with a Dunlin. Clearly this disparity is due to Baird's having a proportionately longer wing, and it has in fact been remarked that the wing-tip overlaps the tail-tip and gives the bird a pronounced "horizontal" stance (Fluke, 1953; Wallace, 1957). Moreover, one observer has commented that Baird's is proportionately shorter in the leg than a Dunlin (Boyd, 1955).
The Semipalmated at Fair Isle struck us as being a rather "upright" bird, due partly to the fact that the wings did not overlap the tail-end, and partly to its proportionately longer legs when it stood alongside a Dunlin. It seems to us that this difference in "jizz" may well be the most valuable field-character for distinguishing between these critical American species, especially on this side of the Atlantic where the Dunlin is their most likely company. The projection of the wing beyond the tail in Baird's is well seen in the excellent photographs of the Sussex-Kent example taken by G. des Forges (antea, Vol. XLVI. plates 44-45). Those of the Norfolk Semipalmated taken by R. P. Bagnall-Oakeley and published in British Birds (Vol. XLVII. plates 27-28) do not depict this bird in the same advantageous position; but other photographs taken at the same time, and which Mr. Bagnall-Oakeley kindly sent to us at Fair Isle, do indicate a wing-tip which falls short of the end of the tail by several millimetres.'
Accepted by E. V. Baxter (1958) in the Scottish Birds, Vol. I. p. 30, under 'Review of Ornithological Changes in Scotland in 1957', stating the date erroneously as 28th May 1957.
D. G. Andrew (1963) in Scottish Birds, Vol. II. p. 342, states that the 1956 Fair Isle record that was accepted by this Committee as the first for Scotland has now been proven to be a Western Sandpiper (Brit. Birds, 56: 55).
D. I. M. Wallace, C. Bradshaw & M. J. Rogers (2006) in British Birds, Vol. XCIX. pp. 460-464, in a review of certain rarities during the period 1950-57, found this record to be unacceptable.
Not included by P. A. Fraser and the Rarities Committee (2007) in British Birds, Vol. C. p. 713, in his graph of previous records.
Comment Misidentified - unknown species. Not acceptable.
