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 |
'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 |
'coburni' left and 'iliacus' right. |
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.
No comments:
Post a Comment