Tuesday 13 October 2015

Thrush Fest

The last couple of mornings have seen good numbers of Redwings and a few other thrushes moving over Billinge with the pattern of movement being similar on both days. Flocks of Redwings in double figures started to appear just after first light and continued periodically until 10am when most movement ceased. I was too busy ringing to do any proper counts but minima of 400 Redwings, 20 Song Thrush and 10 Fieldfare were involved yesterday and minima of 500 Redwings and 25 Song Thrush today. A few high flying Blackbirds were also noted on both mornings but no more than a handful. Woodpigeon migration also started in earnest with hundreds going south on both mornings but there were surprisingly few finches around or on the move.

Although there were a few rather well marked and darkish Redwings I didn't think any were Icelandic birds of the race 'coburni'. However, I did have another Redwing with a wing length of 128mm making it two of that size for this autumn compared with none in my preceding 35 plus years of ringing. I still haven't found the tables showing the full breakdown of wing lengths for iliacus but of 7,364 birds measured in Finland only 0.5% had a wing length over 126mm and Svennson (1992) gives an upper limit of 124 mm and Glutz von Blotzheim & Bauer give an upper limit of 126 mm with variation in sample size probably being the main cause of this difference. Basically wing length isn't much help in identifying Icelandic birds unless you catch a bird with a wing length over 128 mm.

This is the second Redwing with a wing length of 128 mm caught this autumn.

One adult Redwing had orange-red fringes to most of the greater coverts and even had some orangey-red feathers near the thighs.

This same well marked adult Redwing.
Quite a few of the Redwings had ticks on their faces but this bird had a lot more passengers than most.
Whilst separating the races of Redwings is difficult the differences between the races of Song Thrush are much easier to see in most cases. The main British race clarkei is much more richly coloured being much more ocherous-brown above with little or no contast between the mantle,rump, wings and tail and has more buff on the underparts in contrast to the continental race philomelos which is whiter below and the upper parts are more of a greyish olive-brown which contrasts with the browner wings and tail. The pictures below illustrate the difference quite well. All 10 of the Song Thrush caught today were continental birds and only 1 of the 6 caught yesterday was of the British race.

Continental race Song Thrush showing the contrast between the rump and tail.
Song Thrushes: British race on the left and Continental race on the right.
Song Thrushes: British race on the left and Continental race on the right.
Song Thrushes: British race on the left and Continental race on the right.
The thrush fest of the last two mornings has left me itching to back out into the field and I will probably be out again in the morning. There is a bit of a joke there somewhere for those of you who are 'canny' enough to notice.

Combined ringing totals for 12th & 13th October were: Redwing 119; Song Thrush 16; Goldcrest 12; Robin 2; Coal Tit 1; Blue Tit 1; Bullfinch 1, Chaffinch 1; Lesser Redpoll 1. Total 154 new birds.

No comments:

Post a Comment