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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