(2092) Sterna sumatrana sumatrana.
THE BLACK-NAPED TERN.
Sterna sumatrana Barnes, Trans. Linn. Soc, xxii, p. 329 (1877) (Sumatra). Sterna melanauchen. Blanf, & Oates, iv, p. 322.
Vernacular names. None recorded.
Description. A black line running from the posterior lores, through the eye, round the crown and the back of the nape, including the long crest-feathers; remainder of head white; a collar on the neck pure white, shading into the pale vinous pearl-grey of the upper parts ; tail white; first primary dark grey on the outer web, pale grey on the inner web ; other quills very pale grey edged white internally ; whole lower plumage and crown white, the former flushed with delicate rosy-pink.
Colours of soft parts. Iris brown ; bill and feet black, the former with a tiny pale tip to both mandibles, not always present,
Measurements. Wing 220 to 227 mm.; tail 129 to 150 mm.; tarsus 18 to 19 mm.; culmen 31 to 38 mm.
In Winter the ocular and nuchal patch are less wide and defined.
Young birds have the nape dark chocolate-brown; the inner wing-coverts are dark grey-brown and the primaries are dark grey.
Birds in first plumage have the crown brownish and the feathers of the upper plumage with contour-shaped bars of brown.
Distribution. Andamans, coasts and islands of Tenasserim and Malay Peninsula, Sumatra to Celebes ; Seychelles and Ami-rante Islands.
Nidification. The Black-naped Tern breeds principally in June but occasionally in September, perhaps only when the first broods have been destroyed. The sites selected are small rocky islands round the Andamans, Nicobars, the larger islands of the Mergui Archipelago and the Malay States. The eggs are apparently deposited on the bare rocks with no attempt at a nest and are nearly always two in number, sometimes one only. They cannot, I think, be individually distinguished from the eggs of the Rosy Tern but, as a series, are more boldly marked, more blotched and less speckled. Osmaston took magnificent series of these eggs from various colonies and it is curious that each colony seems to have a regular type : in one the eggs are dark and boldly marked, in another paler and more sandy with feebler markings, whilst a third can be recognized by its deeper ground with not very bold markings, intermediate between the other two. Two hundred eggs average 39.6 x 28.6 mm.: maxima 43.0 x 29.1 and 40.3 x 30.0 mm.; minima 34.6 x 28.1 and 40.0 x 25.9 mm.
The colonies number anything from fifty to two hundred pairs, the eggs being laid very near to one another. The birds are very close sitters and do not rise until the intruder is within a few yards, when they all rise together and circle screaming round his head.
Habits. This is entirely a Sea-Tern, never being found anywhere inland and generally keeping to rocks and quite small islands. It lives almost entirely on fish and small Crustacea, Plight and voice are almost identical with those of the Rosy Tern.