Sunday, 22 November 2015

Oxwich Marsh 22 November 2015: the onset of winter

A light northerly breeze at the marsh swung to the west over the morning.  Apart from a half hour period of persistent light to moderate rain, the weather was very pleasant, and the light wind allowed us to put nets across both the open marsh and in the scrub around the feeders.  We initially tried tape luring for redwing and 'crests,' but only the latter proved particularly productive, with small numbers of goldcrest and two chiffchaffs captured.

The totals were as follows:

Species
New
Re-captured
Total
Snipe
1
0
1
Wren
1
3
4
Dunnock
0
7
7
Robin
0
2
2
Blackbird
1
1
2
Redwing
1
0
1
Cetti's Warbler
0
1
1
Chiffchaff
2
0
2
Goldcrest
9
1
10
Long-tailed Tit
2
7
9
Coal Tit
1
1
2
Blue Tit
30
33
63
Great Tit
0
2
2
Chaffinch
17
1
18
Greenfinch
14
2
16
Goldfinch
19
3
22
Total:
98
64
162

The tendency of snipe to use the edges of the net rides results in an occasional bird being incidentally captured (we will have dedicated snipe rides deeper in the marsh when the water levels are lower later in the winter), and this was the case today.  We didn't have a lot of time to study plumage detail, as the rain came in as it reached the processing table, and we closed the nets.

Otherwise, the features of the catch were a fairly exceptional 63 blue tits, controls of goldcrest and long-tailed tit (birds ringed at another site and recaptured at the marsh), a couple of chiffchaffs (one of which was carrying considerable fat) and moderate catches of common finch species.  A single redwing took the year total to 99.

The photograph below shows three dunnocks, all of which were trapped during the same net round:

Dunnocks (Emma Cole)
The uppermost bird was aged as a 1st winter, with the others not specifically aged. The greyish-olive iris of first winter dunnocks typically 'reddens' over the winter, to the more typical adult iris colour of reddish-brown. By November, some first winter birds cannot be accurately aged based on the iris alone, and conspicuous moult limits in the wing that might otherwise help determination are rare.  As a result, may birds cannot be specifically aged, at least by us, with confidence.

During data entry, the age of all three birds was confirmed, as they had all been originally ringed as recently fledged juveniles.  The uppermost bird and one of the others were fledglings from 2015 (so the bird specifically aged as a first winter on eye colour was indeed a first winter), with the third bird being from the 2014 cohort.  

Thanks to today's team of Charlie Sargent, Emma Cole, Suze Lewis, Heather Coats, Val Wilson and Wayne Morris for company and assistance.

Owain Gabb
22/11/2015

1 comment:

  1. We've found a pale lower mandible indicative of first-winter birds. In your blog's photo, that would suggest that the lower-right bird was the other first winter. Inky-black tips to the primary covets can also support this criteria.

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