BirdingNZ.net

By a happy chance I was at the Manatu Estuary for most of today participating in an Oil Spill equipment deployment exercise run by Horizons Regional Council. All four Gull-billed Terns were present and showing, particularly in the morning when the tide was low. The birds were dotted across the flats towards the bollards, but periodically got up and fed across the flats past the sandspit, and upriver. As the tide rose the terns became less obvious, and at one point three flew upriver and around the bend. Over high tide there was just one present, on the sandspit with Red-billed and Black-billed Gulls and Caspian Terns. As the tide started to recede the black-capped adult joined it, and after I waded across the channel I managed to get what should be cracking shots of both birds taking off and flying around. I have no idea where the missing birds were over high tide. So anyone visiting would do well to scan the estuary from the eastern side of the main flat (turn left at the shops on the corner, at the turnoff to the boatramp, then right at the road by the estuary), check any birds on the spit (from Dawick St) and also look from by the bollards by the sand track through the dunes.

In addition to me, the birds were seen by Eila Lawton and Peter Maddison en route back from the OSNZ AGM, Roger Slack from Palmerston North, and Phil Hammond who had left Auckland at 3.30 this morning to drive down for the twitch!

The 2nd-most unusual sighting today would have been the 77 Black Shags lined up along the shore - an unusually large number. Also 43 of the 44 spoonbills present today came up onto the spit, for a pale spectacle (spoonbills, gulls and terns were the only birds there).

Cheers, and photos to follow when I get the chance,

Phil

all 4 were out on the mud, visible from hartley st this morning [wed]

shore plovers still at plimmerton yesterday at dusk

3 more images

Photos of the birds from yesterday. Seems I got to photograph three of them: the black-capped, a first-winter with brownish tips remaining on many upperwing feathers, and one in non-breeding plumage with the outer 5 primaries shorter than the newer inner ones. I think the 1st-winter is missing a primary on each wing - probably P9 on the right wing and P10 on the left. The black-capped bird has 7 new and 3 old primaries, on the left wing at least. Note that the fork in the tail doesn't show when the tail in fanned, but it does in normal flight. Fantastic birds to have around!

Phil

That first shot in particular is a cracker!

Thanks Neil. I sent the photos to Danny Rogers in Australia, who has published on distinguishing Australian and Asian GBTs. He confirmed these are Australian birds (macrotarsa), thought that the bird I suggested might have 9 primaries actually has 10 (I also now think it does, so no complex sleuthing required there) and felt that the final bird I showed in flight is also a 1st-winter, on the basis of its dusky secondaries. The Australian birds can breed pretty much any time when water conditions allow, so you can get widely ranging moult timings. So it looks like there are:
1) An adult with a largely black cap that has moulted P1-7;
2) A first-year that has obvious tips to many upperpart and tail feathers that has done no primary moult (and it's only in juveniles that you get the even-toned primaries across them all);
3) A less obvious first-year with dusky inner secondaries that has moulted P1-5;
4) Another one I have no detail on.

if you want to read about GBTs, look at Wingspan 22, Dec 2004 ("SORTING MIGRANT GULL-BILLED TERNS FROM RESIDENTS") and Emu 105: 145-158 (2005) (Rogers et al. "Gull-billed Terns in north-western Australia: subspecies identification, moults and behavioural notes").

Cheers, Phil

All four birds still present and visible from the platform at the end of Dawick St, actively feeding in the shallows off the spit at 1210pm. Many thanks for the excellent photos Phil and thanks also for doing the detective work re subspecies.

I remember seeing a (presumably Asian) Gull-billed Tern on the north Norfolk (UK) coast many years ago. Do we know if the Asian subspecies has ever occurred in NZ?

Also present on the spit 74 Black Shags, 42 Royal Spoonbills, 6 Bar-tailed Godwits and just a handful of Caspian Terns.

Neil Robertson

Some video of the Gull-billed Terns taken 3 June on Youtube (grey day). The birds in flight are in slightly slow motion which helps to show it dipping down to grab crabs from the mud.
[youtube]http://www.youtube.com/watch?v=nPceUJ38wJQ[/youtube]

That's GREAT! Good stuff.

Phil

Very interesting stuff

Gull-billed terns are more of land birds, than other terns as white-fronted terns, with varied diet of insects, crabs, and less fish, & worms, with fewer skinks. They don't fishing unless they see fish very close to seas surface where they "dip-fishing" with same action as for crabs. These crabs are alert animals and can be hard to catch, so gull-billed terns are fast to grab the crabs before crabs dive into their burrows. Crabs form small part of waders"s & gulls"s diet, so there are hundreds of crabs to keep gull-billed terns happy.
If birds had survived this winter and being a Australian subspecie that can breed around the year, they will breed about between August and March, tends to breed near rich feeding areas as mudflat with lot of crabs & fish, worms.
They breeding in a group on island or on beach. Juvenile plumage-same as winter plumage, but have pale brown tips to pale grey feathers. Moult duration of gull-billed terns: Unknown. May start breeding at 1-2 year-old, when all flight feathers are all adult.
Adult flight feathers are of two genes, with post-breeding moult apply to primaries 1st to 10, with pre-breeding moult apply to 2nd gene of primaries 1st to 6th-8th. Flight feathers are pale grey when fresh, but wear down to dull black as feathers loose grey bloom.
Clinton.