Redwings: coburni v iliacus 2015

I nearly didn't go out this morning because the wind was a little stronger than had been forecast and was near the limit for mist-netting at Billinge. After umming ahhing for bit I decided to give it a go, after all it is late October, the wind had turned south easterly again and you just never know what may turn up. I was reasonably sure there would be an increase in Redwings as there had been a small arrival on the east coast and on the northern isles the previous day including some Icelandic birds on Fair Isle and North Ronaldsay. As a general rule there is a passage of thrushes over Billinge 24 hours after arrivals on the east coast from Spurn northwards and this proved to be the case again this morning.

The first round of the nets produced 13 Redwings and 2 Goldcrest which I would have been happy with as a total for the morning given the conditions. The next round produced another 7 Redwings and 7 Goldcrests which indicated there had been an increase in Goldcrest numbers too. The catching rate then slowed as the cloud cover thinned and the sun tried to break through but there were a few birds in every net round up to 10:30 when I decided to pack up. The final total of 53 new birds exceeded my expectations by some margin and was made up of 28 Redwings, 1 Song Thrush, 21 Goldcrests, 2 Bullfinch and 1 Lesser Redpoll.

Bird of the day and the main reason for this post was a Redwing that I considered to be of the Icelandic race 'coburni'. When I saw it at the far end of 18m net I knew it was likely to be one, assuming I am correct of course. It was darker than any of the other Redwings, was more heavily marked, had striking undertail coverts and even felt bigger when extracted and was in the hand.

Icelandic Redwing (coburni) 27/10/15

Icelandic Redwing (coburni) 27/10/15

Many years ago I read a comment about the identification of Goshawks which said something along the lines of  'when you think you have seen a Goshawk you haven't because when you do see one you will know'. The same seems to apply to the identification of Icelandic Redwings, when you only think you may have caught one you almost certainly haven't but when you do catch one you will have no doubt. As well as looking good for 'coburni' it had a wing length to match and measured 128.5mm. Now I know that is only 0.5mm over the maximum for 'iliacus' and I would never claim one on the basis of that 0.5mm alone but I would have been equally happy with the identification had its wing length fallen well within the overlap between the races.

Now ideally this identification needs to be confirmed in some way and the bird left the odd stray body feather, as thrushes often do, which was collected up and saved for possible confirmation via DNA . Luckily I share this interest in the identification and occurrence of Icelandic Redwings with Martin Garner of Birding Frontiers and with Martin's help and contacts there may be the opportunity to see if the races can be separated via their DNA. If there is any progress with this I will post about it in due course but up until then you can either take my word for it or make your own mind up from the photographs.

RZ06779 is the 'coburni' Redwing and RZ06780 and  RZ06782 were the following 'iliacus' caught and ringed this morning. You may be wondering why I didn't use pictures of RZ06781 and the simple answer is because it was a Song Thrush, it was not that I was being selective in the 'iliacus' used for comparison. Note the leg and feet colour of the 3 birds, 'coburni' is dark chocolate brown while 'iliacus' is mainly pinkish straw although a few can be brownish but certainly not as dark as 'coburni'.

The two birds on the right show significant variation in the extent of the flank streaking of 'iliacus' and show why the differences are not always clear cut and easy to describe.

Same birds and the 'coburni' on the left should be jumping out now if it hasn't done before. If they all had undertail coverts like RZ06779 the job would be easy but unfortunately that may not always be the case. More photographs of other individuals are required.

Please don't get the idea that I think you can always separate the races from their overall appearance or on the basis of specific plumage features as I just don't have enough experience of 'coburni' to say that at this time. It may be possible but at this stage I just don't know for sure and that is why it interests me so much. There may be some overlap in appearance as there is with wing length and the danger with separating very similar races is in focusing on the differences between easily separated individuals whilst understating any similarities that may occur at the other end of the scale.

The final picture (for now) shows today's 'coburni' (left) with a bird that I commented on in a previous post because of its size but was happy with as an 'iliacus', You can see differences but it is far from easy and would be much more difficult at range in the field. I am still happy that the bird on the right is an 'iliacus' despite its size and fairly well marked breast.

Hopefully I will catch and photograph a few more Icelandic Redwings before the autumn is out but if you would like to see my previous post on this subject you can find it here.

Thrush Fest part 2

The good numbers of thrushes that moved over Billinge on Monday and Tuesday paled into insignificance compared with the numbers on the move on Wednesday (14th). Inevitably I was too busy ringing to devote much time to estimating numbers but in the region of 3,000 to 5,000 Redwings were involved with the upper figure probably being nearer the mark. A friend who lives nearby counted over 2,000 from the fairly restricted view point of his garden and after missing some of the early flocks so the upper estimate of 5,000 could even have been on the low side. A few Blackbirds and Fieldfares were also seen or heard and around 30 Song Thrush were noted but others would have gone through amongst the hordes of Redwings.

Many of the Redwings moving over Billinge will winter much further south in France or Spain.

During the morning a total of 138 birds were ringed as follows: Redwing 114; Song Thrush 7, Fieldfare 1, Blackbird 1; Goldcrest 6; Lesser Redpoll 5; Great Tit 3; Coal Tit 1. With so many Redwings about I could have easily caught a lot more than I did but I had to limit the catch to numbers I could safely deal with on my own.

On Thursday (15th) I was out again as it seemed likely that there would be plenty more thrushes on the move. This time as was joined by David Norman of Merseyside Ringing Group and initially it looked like there would be similar numbers of Redwings for a second day. After a very busy start numbers tailed off quite quickly compared to the previous day with around 1,000 Redwings going through along with 100 or so Fieldfare, a few Blackbirds and another 20 or so Song Thrush.

The big Fieldfare movements have yet to come. 

The thrushes attracted the attention of a minimum of 3 Sparrowhawks

Despite there being fewer Redwings on the move we still ended up with excellent ringing total of 111 new birds, 3 retraps and 1 control. Ringing totals were: Redwing 82; Song Thrush 3; Fieldfare 2; Long-tailed Tit 11 (2); Goldcrest 6 (1); Blackcap 1; Coal Tit 1; Blue Tit (1); Great Tit 1; Treecreeper 1; Lesser Redpoll; 1; Bullfinch 1, Sparrowhawk 1. The control (bird ringed elsewhere) being the only Blue Tit caught.

With little change in the weather and the likelihood of more Redwings I was back out again this morning. It was a much quieter than the previous day but at least 500 Redwings went through during the morning. Other sightings included 3 Bramblings with a cracking adult male being caught and a single Crossbill was noted going northeast. Ringing totals for this morning were: Redwing 42; Song Thrush 5; Blackbird 2; Goldcrest 7; Blue Tit 1; Lesser Redpoll 3; Chaffinch 3, Brambling 1. A total of 64 new birds.

Most of the Song Thrushes that have been caught recently are greyer continental birds like this fine example.

They don't get much greyer than this and look very different to the British race clarkei. 

...and here is an example of the warmer buff and brown British race clarkei for comparison. 

Finding this adult male Brambling in a net today was a really nice surprise. Only 2 had been heard going over before this one was caught.

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.

Redwings: coburni v iliacus

I think I was a little too cautious in my post 'More of the same' (link here) with regard to the photograph of a Redwing that showed characters of the Icelandic race 'coburni'. I suggested its appearance possibly fell a little short of the mark but if anything fell short it was my experience of birds from the Icelandic population (nil up to then). I caught another dark and heavily marked bird yesterday and it stood out as much if not a little more than the previous bird did which prompted me to reconsider that earlier note of caution. It also prompted me to do some homework and I have been trawling the internet looking at photos of the races and reading up on the subject. I am now certain that yesterday's bird and the previous bird (caught 16/11/14) are Icelandic Redwings.

Birds of the Icelandic subspecies (T.i.coburni) are marginally larger and darker than nominate birds from northern Europe (T.i.iliacus) but only around 14% of Icelandic birds have longer wing lengths and therefore relatively few can be separated on size. Both birds had wing lengths that fell in the upper part of the overlap in the wing length ranges with yesterday's bird being 127mm (right on the upper limit) and the first bird had a wing length of 124mm. Published wing length ranges vary depending where you look but I have gone with 126/127mm as being the upper limit for nominate birds largely based on a paper that considered occurrences on Heligoland (Germany) which can be found here.

In terms of appearance 'coburni' is described as being slightly darker and are generally more heavily marked and having looked at a lot of images of both races there appears to be less overlap in appearance than there is in size. However I do feel there was a bias towards showing obviously darker birds amongst the examples of migrant 'coburni' photographed outside Iceland which is only to be expected when the separation of the races is not always clear cut. Another feature for separating the races is the colour of the legs and feet which are dark horn brown in 'coburni' and pinkish-flesh in 'iliacus' and this was very obvious and can been seen in many of my photographs.

Redwing of the Icelandic race 'coburni', Billinge 20/11/14

The following series of photos shows the same bird with a fairly typical bird of the nominate northern European race 'iliacus' that was caught the same day and photographed in similar conditions. 

'coburni' above and 'iliacus' below.

'coburni' left and 'iliacus' right.

'coburni' above and 'iliacus' below.

The following images are of the previous Icelandic bird caught on 16/11/14. On looking at these images again I don't know why I was cautious about fully attributing it to the Icelandic race. 

Redwing of the Icelandic race 'coburni', Billinge 16/11/14

Redwing of the Icelandic race 'coburni', Billinge 16/11/14 (same bird but appears to have a slightly paler throat and upper-breast from this angle).

Redwing of the Icelandic race 'coburni', Billinge 16/11/14

...and here is a collage showing how it compared with a lightly marked nominate bird caught the same day.

'coburni' left and 'iliacus' right.

The final image below shows a collage of both Icelandic birds with what I consider to be a heavily marked nominate bird (lower right) and a more typical nominate birds (top right). Although you can't really see much of the upper parts you can see enough to appreciate how much darker both Icelandic birds are. The upperparts of the Icelandic birds are what I would describe as a dark olive earth-brown whereas the nominate birds are more of a mid toned warm brown. The other thing to note in this image are the feet; darker horn brown coloured in the Icelandic birds (left) and pinkish-flesh coloured in the nominate birds (right). The strength, size and colour of the markings on the underparts largely speak for themselves but there is a little more variation in them.

Upper left 'coburni'; lower left 'coburni'; upper right 'iliacus'; lower right 'iliacus'.

If you are interested in comparing other images of migrant 'coburni' photographed in the UK examples can be found  here (Bardsey),  here (North Ronaldsay),  here (Fair isle),  here (Norfolk).

For images of 'coburni' taken in Iceland you can view images taken by Jakob Sigurdsson here and here. Other images by Gudmunder Geir's can be found here.

It is also worth a second look at the 'We Bird North Wales' blog post on this subject here.