Saunders's Terns at the Cocos (Keeling) Islands

Subject: Saunders's Terns at the Cocos (Keeling) Islands
From: "Mike Carter" <>
Date: Tue, 13 Mar 2007 18:31:22 +1100
This is a follow-up to my trip report posted yesterday to give more detail on the Saunders's Terns.

On 23 November 2006 Ian McAllan saw six small terns on South Island in the main atoll of the Cocos (Keeling) Islands. As the birds were in non-breeding plumage Ian was unsure as to their identity but from the small image photos he obtained, Dion Hobcroft and myself suggested that they were Saunders's Terns. My opinion was based on the very black outer primaries contrasting strongly with a broad white triangle on the rear of the wing and a darkish grey centre to the rump and tail contrasting with white outer rump and tail. Others, including Ian himself, considered that this was not inconsistent with some non-breeding Asiatic Little Terns. Distinguishing these taxa, sometimes considered conspecific, is difficult and controversial, especially in non-breeding plumage. The presence of a small flock rather than just a single bird suggested that they might be wintering migrants rather than vagrants and since identification would be greatly simplified if the birds were in breeding plumage, I decided to time a visit to catch the birds in that plumage before they departed northwards to breed, presumably in the Arabian Sea if my ID (or hunch as some say) was correct. They are known to occur in the Maldives perhaps as migrants but may breed there. Also maybe at Diego Garcia. From their moult pattern I'd be surprised if they bred on Cocos. Conveniently, Richard Baxter was running a tour to Cocos at the end of February 2007 so Colin Judkins, Grant Penrhyn & I timed our visit to overlap with them. This timing worked perfectly. When National Parks staff on Cocos took the three of us to South Island on 28 Feb 2007 the birds were still there. We saw up to 9 birds together at least 5 of which were adults in full or near full breeding plumage. Some of the others were in immature plumage. We photographed most if not all of them. We were there from 11.25 to 14.40 on a rising tide leaving about an hour before high tide. Two visits by National Parks rangers in the intervening period had not seen these terns and they were not seen when Baxter's party went at low tide next day but his second party watched seven feeding and in flight on 7 March for some 15 minutes near high tide. Some locals report having seen small terns plunge diving in the area in recent years so they could be regular.

The Terns frequent the lagoon shores of South Island, particularly Telok Semberang a bay at the western end of the island. Huge areas of this bay and more northerly and easterly adjoining bays form extensive flats at low tide. The substrate here has a very shallow muddy surface apparently not found elsewhere in the atoll. It was the only coastal area supporting a reasonable population of waders (10 species totalling 120+ birds). The Terns appeared to be assembling to loaf at high tide near Hujung Pulu Jau an islet off the western tip of South Island. The only other terns in the area are White Terns, which feed in the surrounding ocean and nest and roost in trees. Access to the area is difficult as the approaches from the lagoon are very shallow, too shallow for all the local boat hirers but small private tinnies or canoes can assist passage to the island or you can wade 3 km each way wearing sandshoes to avoid being cut by coral!

In breeding plumage, important characters for distinguishing them from Little Terns are slightly smaller size, white forehead smaller and square-cut, no white supercilium, upperparts paler, no obvious contrast between back and rump/tail, centre rump and much of tail grey rather than white, legs dark brown not orange or yellow, outer primaries contrastingly deep black and shafts black not grey, tail especially streamers very short.

Mike Carter
30 Canadian Bay Road
Mount Eliza  VIC 3930
Tel  (03) 9787 7136


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