Wednesday, 14 December 2016

Crawford: 12/12/2016 and wing moult in first year Blackbirds

I don't know what is happening with thrushes and Redwings in particular but there seems to more nocturnal movement than is usual at this time of year, especially given the absence of any cold weather. Some large nocturnal movements of thrushes were noted at Spurn Bird Observatory towards the end of last week and some of those continued in daylight hours at Spurn but more so at Sunk Island. These unexpected movements attracted the tongue in cheek comment 'Mild weather movement?' in the list of sightings for 9th December on the Spurn Bird Observatory website.

I have heard Redwings overhead well before first light on numerous occasions recently and that happened again when I was loading the car to go ringing on the 12th. When I got to Crawford I heard the calls of a few more Redwings going over in the dark in the short time it took me to set up the line of two nets. Whatever the reasons are for these movements it seems to translate into more Redwings being in the area and good catches at dawn, although they are remarkably inconspicuous during rest of the day. The net result, no pun intended, was that I caught another 16 Redwings on the 12th which took the number ringed so far this month to 131. It also took the number ringed since early October past the 1100 mark and to 1110 to be precise. How long these nocturnal movements and dawn catches will continue is anybody's guess but now that I have mentioned them they will probably come to an abrupt end. I will find out soon enough as I hope to get out to Billinge and/or Crawford later this week.

This is the one thousand, one hundred and ninth (1109) Redwing ringed this autumn/winter. Yes I know it is an odd number but the light levels were too low when number 1100 came along.
Whenever there are a good number of thrushes around one or more Sparrowhawks are never too far away and that was also the case on the 12th. Their presence sometimes reduces the catch of Redwings, especially when they make frequent sorties, but that is quickly forgotten about when one ends up being caught in one of the nets. Sparrowhawks have a bit of a reputation for getting out of nets, especially the larger females, but I have been lucky enough to catch 10 since early October with 5 of them being females.

2nd year Female Sparrowhawk. It is bigger than it looks in this photo. 
Blackbird was the only other species handled with 8 new birds and 2 retraps being caught. One of the first year males was particularly interesting because it had replaced some of its secondary flight feathers in both wings, which first years don't normally do. There was some asymmetry to the moult but it certainly didn't appear to be due to any accidental loss of feathers.

Eccentric moult in 1CY Blackbird LK6922 caught at Crawford 12/12/2016
A bit like the stockamsel plumage Blackbirds that I wrote about in my last post this was the second first year male Blackbird to come my way that had undergone a partial moult of the flight feathers. The first was a Blackbird that I retrapped in the garden on 22nd November, it had been ringed as a juvenile on 7th August so wasn't from a particularly early brood but it definitely made it a bird of UK origin. The moult of this bird was far more extensive and involved some of the primaries, primary coverts and secondaries, and all of the greater coverts, tertials of both wings, although there was some asymmetry. The entire tail had also been replaced.

Left wing of 1CY Blackbird LK25176 retrapped in the garden 22/11/2016

Tail of 1CY Blackbird LK25176 retrapped in the garden 22/11/2016
In recent decades it has become more common for finches to undergo a limited moult of the flight feathers as part of their (partial) post-juvenile moult but this phenomena appears to be a far more recent occurrence in Blackbirds and these two examples are the first I am aware of for the UK. A search of the Internet revealed a short paper about a juvenile Blackbird that was found moulting its primaries and secondaries in Poland in 2004. That appears to be the first account of a juvenile Blackbird replacing its primaries and secondaries and moult aficionados can find that paper here or by searching for the reference below.

As for the cause of the change in the extent of the pj moult in some birds I would put climate change as the number one suspect but as many of the species involved are also frequent visitors to gardens the more extensive and much improved quality of food provided in gardens may also be playing a part. It is certainly an area that is ripe for research and hopefully it will become something that the BTO will take more of a lead on by encouraging ringers to record and report any examples they come across.

ZieliƱska M., ZieliƱski P., Mokwa T. 2005. Juvenile Blackbird (Turdus merula) moulting primaries and secondaries. Ring 27, 1: 121-123.

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