birding-aus

Common Tern observation

To: Chris Corben <>
Subject: Common Tern observation
From: Jill Dening <>
Date: Mon, 13 Apr 2009 09:50:57 +1000
Hi Chris,

 Trouble is, those northern shores have apparently been
nuked - thousands of waders and hundreds of terns reduced to a handfull,
from what I've seen and heard.
You have heard correctly. It's now a shorebird and tern wasteland.
But if that was so, Common Terns in general may have declined
more in visibility than in numbers.
I would like to think this, but my regular questions of boaties suggest otherwise. Ivan Fien is a local birder, who was CEO of Redcliffe Shire for many years, and also a longtime boatie, in the northern part of the bay and offshore, going back to the 60s. He said he birded with you years ago. He reinforces this view. However, his memory goes back to the time when he was a regular birder with the likes of Peter Slater, and they found their first Common Terns in the bay in the mid 60s. Until then they had never seen Common Terns in the bay, and had a deal of difficulty working out what they were. Ivan became a serious birder around 1960. So they haven't always been here. Ivan was astounded when I came up with thousands of them around the late 90s, and even more so to be there with me surrounded by them in Caloundra. Back to your question; I would really like to have it proven otherwise, so I keep asking during winter. Commons certainly appear in the northern part of the bay, but not now in the flocks you have seen. Buckley's Hole on Bribie Island is a good spot to find the odd one.
In general, judging the darkness of primaries from single photos can be very
deceptive. I'd be wary of such a generalisation.
True, I have made this point myself, but there is such limited material available with ages attached. One would hope that the authors of the book have chosen a photo because it shows the features they want the reader to see.

which are far paler than the immature of the same month. If this photo is
indicative of longipennis, our 2nd summer birds should still have darkish
primaries.

I'm also not sure what you mean by that last sentence.
Sorry, it's getting complicated, and I am not explaining myself well. I was looking at the apparent difference between the Ps of an adult and a 2nd year bird in August in the book, and taking it back mentally to how I would expect the Ps of those same birds to look in April. And then trying to layer that on what I know about longipennis.
A second year bird in
August will be just over a year old (say 14 months), and in first Alternate
with the beginnings of second Basic (the inner Ps), and maybe even some
retained, Juvenal, outer Ps (trashed!).
Yes, understood.
The bulk of the Ps would be
Formative (ie they have been replaced once by a special molt seen only in
first cycle birds). 
OK, didn't know about this.
A second year bird now (April, at 22 months age) would
be in second Alternate with second Basic outer Ps and second Alternate
inner Ps.
Now you are giving me the information I have been trying to work out, thank you.
So essentially, a bird which was a second year in August (14
months old) would have molted probably all its feathers again by the next
April, when it is 22 months old.
Do you think this bird would be separable in the field on colour of the Ps? Or would it blend in with the adults?
A bird which was a second year in April (at
22 months) would be a third year in the following August (at 26 months).
Yes.
Just to confuse things more, please note the distinction between "second
year" as in "second calendar year" and "second year" as in "second cycle".
In April, a second calendar year bird would be in its first cycle, and I'd
have called it a first year bird (10 months old).
Yes, so would I.
I don't have a copy of Olsen and Larsson handy, so I can't see the picture
you refer to. But if it was really a third year bird (at 26 months) then you
could argue that its dark primaries would have been darker in the previous
April when it was a second year bird (at 22 months), since they would be the
same feathers. But in fact, second year birds can be identified up to at
least December (at 18 months) by their PALER outer primaries, since these
were replaced more recently than than the outer primaries of adult birds.
Once the outer primaries have been replaced (as they would have by now),
that won't help. The paper attached by Danny does a great job of talking
about ageing for the nominate race, and there's no reason to think it will
be much different for longipennis.
OK, that's really helpful, and answers the question above. I haven't had time to read the paper from Danny, and won't before I leave in the morning - I'll read it as I travel.
In summary, at present (April) most first year birds (at 10 months) will
look like Basic birds and have retained, Juvenal outer primaries,
though it's quite possible some may be more advanced and harder to tell from
older birds. Second years (at 22 months) will be very hard to tell from
adults, or in some cases from first years.

I hope the above isn't too confusing. Complex Tern would be a better name
for Sterna hirundo!
I think the Little Tern is even more complicated, so let's consider this easy! No, it's good. Much of it I knew, but you have filled in some vital gaps for me.

Chris, this is absolutely wonderful, and I can't thank you enough. I won't pass a test on it right now, but I have taken it in. With the time difference, you won't get this for several hours. I probably won't be able to pick up emails for a few days now, but if there is any more on this, I will get it later.

Then I want to ask you about your knowledge of the secondaries! I am wondering if they might be the last feature which visibly separates adults from immatures in the field.

Cheers,

Jill

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