Hi everyone,
Well, the jury is officially still out on the identity of the dark Jaeger
foto posted last week. But those jury members who were on board are sticking to
the ID of Long-tailed Jaeger, as are one or two others who made some very good
points about the ID. There was little interest in the exercise (I should have
called the message "collective noun for Jaeger ID"), but the most interesting
point to be made is that most people who responded to the fotos (that weren't
on board the boat) called that dark bird an Arctic Jaeger. If, after reading
this summary they still feel it is, please tell us why.
This is the bird -
http://www.flickr.com/photos/callocephalon/3329565621/in/photostream/
I will attempt to summarise the reasons why we are confident that it is a
Long-tailed Jaeger - a first year dark morph bird. Thanks to all those who
helped with this too and apologies for not getting it back here sooner.
First and foremost are those points that are much easier judged in the field
- structure, jizz and of course, behaviour. Structure is very important but can
be very hard to judge in fotos. Our bird was a slightly built creature that,
combined with the typical Long-tailed jizz and behaviour, left us in no doubt
on the day that what were looking at was a Long-tailed Jaeger. It was one of
several Long-taileds seen on the day, particularly out on the shelf when we had
up to a dozen within sight of the boat - this one just happened to be a dark
bird, hence the reason for Tobias' original posting. Those of us who are
sticking to our original ID are seeing this more of an exercise in how
difficult identifying some birds in fotos can be (and is particular, Jaegers -
e.g. see that link I included in my earlier message on the topic - Jaeger ID
from fotos is a hotly debated topic in the UK etc). This bird behaved exactly
the same as the other Long-taileds and
never once approached another bird in harassment. The mention of it having a
broad base to the wings I think comes back to a matter of proportions and on
this bird it still fits that of the Long-tailed Jaeger.
The bird has a short, fairly stocky bill, typical of a Long-tailed. Admittedly,
on some of the other images (see link later in message) the bill appears longer
but those images show typically plumaged Long-tailed (see the primaries). What
is also evident on the bill of these birds is that Long-taileds bills are about
half black / half pale (i.e. the dark gonys end of bill equals roughly half the
bill length). On Arctics it is less than half black because they have a
proportionally longer bill (and in which the dark gonys area ends up being less
than half of the bill length). The bird in question's bill is at least half
black. This is more clearly seen in my foto:
http://i178.photobucket.com/albums/w248/Brewerbackpacker/Wollongong%20Jaegers/UnidentifiedJaeger.jpg
This feature is illustrated well in the link Tom Tarrant sent earlier. Check
out the bill on the Dark Juvenile for Long-tailed at
http://sibley.enature.com/species.asp?speciesID=2361#img and compare it to the
Dark Juvenile for Arctic at
http://sibley.enature.com/species.asp?speciesID=2572#img
Also typical of a Long-tailed is the neat barring on the underwing and
undertail coverts. This can be clearly seen in both fotos of the dark bird.
Furthermore, there is no hint of gingery, yellow tones in the barring, which
would be likely seen on an Arctic.
Another very useful ID point for Long-taileds is evident on the upperwing,
where the dark secondaries contrast sharply with the far paler, grey-brown
secondary coverts. Someone referred to this as 'the wedge' and is believed to
be diagnostic on Long-taileds (though, as they pointed out, rarely mentioned in
texts). This dark wedge isn't really picked up in the images of the dark bird
but can be seen on Long-taileds in other fotos taken on the day. Tobias has
updated his image set and has included some more fotos of Long-taileds,
including some ID pointers. See:
http://www.flickr.com/photos/callocephalon/3332730406/in/set-72157614789756447/
This 'wedge' is also drawn in the eNature ID link. One of the other key ID
points in those images clearly seen on Tobias' link is the white primary shafts
on only 2 or 3 of the outer primaries. This can be seen on my image of the dark
bird.
I don't want to write too much more - I don't have a fraction of the experience
in Jaeger ID as some people out there, so if there's anything more needed to be
added...or if I'm just straight-up wrong, please let me know. It would be great
to get concensus on this bird.
Mick
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