Saturday, 6 December 2014

Oxwich Marsh 6 December 2014: an unexpected snipe and an odd blackbird

We didn't plan to put out nets for snipe this morning, as the overnight forecast suggested temperatures would be very low first thing, and we didn't want frosted nets (they have to be in place a good couple of hours before first light).  In the event, it didn't get as cold on the coast as a couple of miles inland, and we could have got away with it - very frustrating.  Having made the decision, however, we limited ourselves to three nets in the fen meadow and a further three in willow and thorn scrub (total 340 feet).
 
The day was bright, with little cloud and barely perceptible wind.  The catch of 48 was as follows:
 
Species New Re-trapped Total
Snipe 1 0 1
Great Spotted Woodpecker 0 1 1
Wren 0 1 1
Dunnock 0 2 2
Robin 0 1 1
Blackbird 1 1 2
Long-tailed Tit 1 3 4
Blue Tit 1 7 8
Great Tit 0 2 2
Chaffinch 5 0 5
Greenfinch 6 1 7
Goldfinch 5 7 12
Reed Bunting 2 0 2
Total: 22 26 48
 
Despite not attempting to catch snipe, we caught one.  A bird flew into the fen meadow nets as we were putting them up - the first we have caught away from nets specifically set for them.  Other highlights were limited to two reed bunting and a reasonable catch of finches.  Tit totals were thankfully manageable.  This was only the second session of the year when re-trapped bird numbers exceeded newly ringed birds.
 
We had one oddity, a blackbird that showed an unexpected moult pattern.  This was a re-trapped bird.  Although we did not have the information at the time, and each bird should be aged according to what you can see in the field (as opposed to checking back to when it was initially ringed for clues as to age), we now know that this bird (LA75666) was ringed as a 3JP (a recently fledged bird in predominantly juvenile plumage but showing post juvenile moult) in mid September.  We have no reason to doubt this determination, and juvenile male blackbirds are not particularly challenging to age.  However, as can be seen from the photos below, there were two generations of primary feathers present when the bird was recaptured this time around, which does not fit either adult or juvenile blackbird.  Both wings showed the same pattern of moult.

Juvenile blackbirds should not replace the primary feathers (or primary coverts) as part of their post juvenile moult.  However, adult birds should moult the wings entirely, resulting in no contrast in the flight feathers.  First winter males have dark bills that gradually become yellow over the winter.  Bill colouration here indicates a first winter bird.  Pictures are below:
 
Blackbird LA75666
 

Blackbird LA75666 showing different generations of feathers in the wing.
The blackbird appeared to have replaced its tertials, all of its coverts and several primaries (see the middle of the three arrows on the photo above), but had also retained some secondaries and its inner-most primary (see left arrow), and its outer primaries (right arrow).  It can be seen that retained feathers were bleached, more worn and pointed, compared with the darker, more rounded replaced feathers.  The bird had also replaced all of its tail feathers.

Any comments on the blackbird - particularly experience of similar birds from other ringers - would be useful.  Are we missing something here?

Thanks to Heather Coats, Cedwyn Davies, Emma Cole and Darren Hicks for company and assistance this morning.

Owain Gabb
06/12/14.

 

2 comments:

  1. Quite a bizarre bird! Pretty odd it replaced middle primaries (as finches do), but even odder it has moulted all primary coverts...

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  2. Thanks Mark. Useful to get some thoughts from outside the group. Glad you also thought it was a fairly odd one - always nice to know we were not being completely dopey!

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