Possible Arctic and Common? Tern at Waipapa point, Catlins

[Davidthomas]

Hi all,

Was passed these back of the camera shots from
Johannes Fischer who is out at Waipapa Point today (26/12/2018). The first bird to me looks dead cert for an arctic tern, short stubby legs, dark wing coverts and dark primaries, a compact dark cap and entirely pure black bill that isn’t overly long.

The second is of a bird that looks slightly shorter legged, a nice dark carpal bar, a receded black cap, that’s quite clean and behind the eye, plus dark outer primaries. Less sure on this one though. Looking for thoughts.

Will try to edit with non-BOTC photos later when Johannes gets back to accomodation.

Cheers,
David and Johannes

[Ian Southey]

The first bird looks like a White-fronted Tern to me. Big body, short wings, head pattern, legs hidden or slouching. As far as I can see from the photos, the second one might be an Arctic Tern - better shape and head pattern. Also moult looks like first winter - worn juvenile wings and fresh feathers on the back. I think quite a bit certainty might come from the real pictures.

Ian

[Davidthomas]

Morning Ian,

Apologies I fell asleep before Johannes sent me the actual photos. And they are as follow

[Steve Wood]

Hi David,
My call is the first 4 images of this selection are White fronted and the last three shows an Arctic.
General size compared to White fronts looks very small, short legs and nice round head.

[RussCannings]

I agree with everyone on the Arctic (first winter bird with lots of retained juvenile coverts), but why aren't the other birds immature Commons? I would have thought that any 2nd summer WFT would show obvious white "cut backs" (to quote Sav) in the inner edge of the primaries which is not apparent in either bird. Johannes felt that both birds appeared slightly smaller than nearby WFT which is also intriguing. It's a pity that there are no comparative shots for the possible Commons.

Would appreciate hearing from others, or if Ian/Steve still think WFT based on structure and plumage, it would be great to get more specifics so we can all learn something.

Waipapa Point certainly deserves more birding attention as it must be one if the best road-accessible seawatching spots in NZ yet how many Kiwis have been there? Same for Slope Pt.

Russ C
Ternless in Morrinsville, NZ

[Ian Southey]

Russ

My immediate impression is White-fronted Tern because it has a body like a brick and the wings aren't long enough. The head should look a bit flatter, the bill a little shorter, the legs longer so it may stand taller at times and it should be obviously a little darker with contrastier white bits.

The primaries look black because they are very worn - the silvery coating they have when fresh has been worn off on the white upper edges has been almost completely worn away. Bear in mind that a second summer tern is moulting primaries now, this one is half way through, so they are as worn as they will ever get. What you can see on the second picture is a tiny bit of the inside of the outer primary and the black stripe above the shaft of the feather is just too narrow for it to be a Common Tern.

Look critically at any flock of White-fronted Terns for long enough and you will find tremendous variation including in size and many other things. That's how I taught myself terns - it gets easier with practice. There are pictures and comments in earlier threads - I used to post pictures of Common Terns when I had the good fortune to get useful ones - maybe a while ago now...

Ian

[RussCannings]

Thanks Ian,

I've noted the head shape previously so that's helpful to know it's a useful feature. No doubt wear is playing a factor as you say; just thought they'd have even less black that way--but I suppose not if they're more worn on the inner web.

For contrast, here are some immature and old juvenile (and adult) WFT from the Taranaki Coast earlier this year. The younger birds are noticeable with their black carpal bar and more black in the primaries, but as you can see--all have significantly more silver and white in the inner primaries and the black of the outers is limited. The farthest right bird shows those diagnostic cut-backs.

WFTs1.jpg (79.02 KiB) Viewed 2615 times

Something that I haven't heard mentioned but seems to crop up in photos of longipennis Common Terns v White-fronted is that a lot of Commons show thin white spectacles. Has anyone else noted this?

Thanks as always for the great discussion.

Russ C
Morrinsville, NZ

[Steve Wood]

Hi Russ,
Another feature that I have found helpful for separating Common's, especially if they are among White Fronts, is they tend to be a slightly darker grey on the mantle. I also concur with Ian's comments that White Fronts can be hugely variable in size, shape, bill structure etc.
Common Tern at Motueka 2016.

[RussCannings]

Cheers Steve,

I asked Johannes about the mantle tone earlier but unfortunately he didn't scrutinize that aspect at the time. Thanks for adding that and providing the pic.

Russ

[Ian Southey]

I was once rash enough to write on tern ID - it's a two parter - and the second one includes the back cover.
http://notornis.osnz.org.nz/system/file ... 202013.pdf
http://notornis.osnz.org.nz/system/file ... 202013.pdf

It's not the last word, just the best I could do at the time so others may have more to add. I think the hard birds to identify are the White-fronted Terns - once you know you have something else it's pretty easy.

There will also be plenty of pictures if you search the forum.

Ian