ps. all photos are of the same bird after the first obvious photo of a bird with a ring (please note, the bird in flight, the ringed bird is the one on the deck, without a pink rump).
Sunday 7 December 2014
The Cemlyn Twite are from Gairloch near Ullapool
There have been upto 18 Twite recently, with 6 (and now 5) remaining loyal to the ridge. Last winters storms breached the ridge but spread the seeds of the Yellow horned Poppy over a larger area leading to a bumper crop of seeds. Despite feeding, they still seem to be prefering their natural food source. They are quite approachable and I managed a few photos of the ringed individual. Thanks to help from Dawn Balmer and Mark Grantham from the BTO, Mark has pinned it down to one of two birds. Both from this summer at Gairloch near Ullapool in Scotland. Can anyone age this bird for me? Steve Stansfield? Also Robert, can you comment on your findings of Twite on Fair Isle and North Ron please? Cheers Steve
ps. all photos are of the same bird after the first obvious photo of a bird with a ring (please note, the bird in flight, the ringed bird is the one on the deck, without a pink rump).
ps. all photos are of the same bird after the first obvious photo of a bird with a ring (please note, the bird in flight, the ringed bird is the one on the deck, without a pink rump).
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On Fair Isle where they breed, we were often getting changeovers in birds with North Ron, shown through a colour ringing project. We were often getting contradictions in the ageing of the birds between the two sites from the BTO. We would quite often have known adult birds (through the ring numbers) and get reports of it being re-trapped as a juv, and vice versa with North Ron having known aged birds and we got them wrong, subsequently we ended up having to put most of them down as (unknown age). This shows how difficult they are to age.
ReplyDeleteSaying that Photo 10 (back on) doesn’t show a particularly sharp tail tip perhaps indicating that it isn’t a juv but I’m not used to seeing these birds in December. It could be quite abraded by now.
Agree that Twite can be tricky to age. Moult limits can be subtle. For me, this bird appears to be 1cy (EURING 3). The birds is heavily worn across all the flight feathers, in line with what I'd expect for a 1cy. Additionally, shape and abrasion of tertial, secondaries and primaries fit with expectations for 1cy; primary coverts, from what we can see of them, too. GC9 (innermost visible greater covert in the photos) appears less bleached and less worn than the rest of the visible GCs; it's also slightly longer than the other GCs. This apparent difference is visible in more than one photograph. There's a need to be careful since inner GCs can sometimes be protected by overlying scapulars, thus become less worn, but in this case the change between GC8 and GC9 appears sudden and even the exposed tip of GC9 is still much less worn. There also appears to be subtle difference in colour, blacker centre and more saturated feather tip, as would fit with juvenile vs adult-type greater coverts (possibly the result of bleaching, possible the result of plumage difference, possibly the result of both). On balance, it appears to be a (post-juvenile) moult limit.
ReplyDeleteThe median coverts strike me as slightly odd: I've never seen a bird of either age class show such worn MCs, but I've never seen a Twite that hasn't moulted them all during the autumn moult. That could mean that this bird has retained these. I can't comment on how unusual that is though I can say that I have seen other finches e.g. Greenfinch, Siskin that have moulted only a couple of inner MCs (could be hidden under the scapulars in these photographs) and have moutled only GC9 – so the moult wouldn't be entirely unexpected if it follows the same general pattern is in other finches.
Finally, the tail is definitely not juvenile. Frankly, it appears in too good quality to have been moulted in autumn (either post-juvenile or post-breeding). I've seen a fair number of Twite that have lost either a large section of or the entire tail. This sort of "accidental moult" would product an adult-like tail and would explain, if it were to have happened relatively recently, the freshness of the tail. A juvenile tail makes it a juvenile bird, but an adult tail on a small Passerine like this doesn't necessarily indicate that the bird is an adult.
As for basing the ring number on the age of the bird like this that is tough to age in the field, even with such excellent photos and a considerable analsys... I wouldn't. Although it's always a fun game to play :)