Sunday, April 6, 2014

Two-barred Crossbills at Lynford Arboretum

At the beginning of the year I had a chance to see the 'controversial' Two-barred Crossbill at Lynford Arboretum in Norfolk but I was unable to get any photographs. I was back the other day and this time there were at least three birds present. There had been reports of five birds and I managed to get some reasonable shots of a couple of them. The first report of these crossbills, I think, was back in July 2013 when a female and three juveniles were seen and reports continued until 30th July. Later in the year at least one genuine adult male was present and this was presumed to be a new arrival. There were reports of Two-barred Crossbill running into October but then they ceased for a while. Towards the end of 2013 and into 2014 however, a new bird was being reported but instead of being generally accepted as a TBC it was widely regarded as being a Common Crossbill with heavy wing-bars or a hybrid Common/Two-barred. Reasons for it not being a genuine Two-barred include: weakish wing-bars that do not broaden; lack of white tips to the tertials; an apparently strong bill; orange rather than pinkish plumage; 'it just doesn't look right' and the fact that no one had heard it call - Two-barred Crossbill has a distinctive toy trumpet-like call that is weaker and higher pitched than that of the Common Crossbill. The fact that nobody had heard this bird call does not rule out Two-barred of course but it didn't help clinch it!
Male Two-barred Crossbill Loxia leucoptera - Lynford Arboretum April 2014
 These pictures, taken last week (April 2nd) at Lynford clearly show two different male Two-barred Crossbills, one of which is better marked than the other. All of the guide books state that one of the distinctive plumage features of a Two-barred is 'clear cut, broad white tips to the tertials' (Collin's Bird Guide). Neither of these birds show this characteristic yet I doubt if anyone would dispute their identification. So what do we learn here?
Male Two-barred Crossbill Loxia leucoptera - Lynford Arboretum April 2014. Clinging to tree trunk.

I was with Paul Stancliffe and in discussion we agreed that the white tertial tips had probably worn away - meaning that this feature is not a reliable clincher for a Two-barred (Though it would be if present!)  I posted Paul these pictures and he has added the following interesting and thorough thoughts on the plumage of these two birds:
'Having done a bit of reading, I have both of these birds as 1st winter Two-barred Crossbills. Clearly one is more adult like than the other.
Both of these birds have done a partial moult since fledgling and the more adult like bird has, it seems, replaced all, or certainly most, of its greater coverts, median coverts and lesser coverts. It has retained its juvenile tertials which are now worn and show very little trace of the white edges and tips. This bird also has a yellow rump which I think is also indicative of its age, but I can't find any reference to this and it might just be a feature that some adults show -I don't know.
The younger looking bird has only replaced the innermost greater coverts and retained the rest which are juvenile type. It has also not replaced all of the median coverts but it is difficult to see how many are new and how many are retained. From the photograph it looks like it has also retained most of the juvenile lesser coverts which look to have brownish centres and buff tips.
This Bird has also retained its juvenile tertials which are worn like the other bird.
Both birds, or at least the more adult type have white tips to the uppertail coverts which according to Svensson is diagnostic of Two-barred Crossbill. This feature is harder to see on the younger looking bird but does seem to be present.
The adult type bird seems to have moulted its tail but I can't be absolutely sure of this as there is no reference to what an adult tail should look like. However the tips look broad and rounded.
Hope this helps'

Male Two-barred Crossbill Loxia leucoptera - Lynford Arboretum April 2014 Bird 2.
 The bills on these birds did not look any weaker than the bills on the Common Crossbills. To me they look as strong and as large. There were Common Crossbills present and I couldn't detect any noticeable differences. Maybe with better views this feature would be noticeable but I would argue that it is a tough one to call in the field without good views and the chance to compare species.
If you carry out a search on the internet you can find lots of photographs of the controversial bird and one of the striking things is how different the hue of the bird is depending upon the light and the angle of view. In some it is a dark orange-red and in others it is a brighter pinkish colour.
Male Two-barred Crossbill Loxia leucoptera - Lynford Arboretum April 2014. Bird 1
 The only feature of that over-wintering bird that is now left is the weakness or not of the wing-bars. The decision to make is: Is this a Common Crossbill with very heavily marked wing-bars or a Two-barred with very weak wing-bars? (Or a hybrid!). Personally I go with the weakly marked Two-barred school of thought. It looked good for a first-winter male to me.
Male Two-barred Crossbill Loxia leucoptera - Lynford Arboretum April 2014. Bird 1
 On a different note these birds exhibited some interesting behaviour. They both preferred to cling onto the main trunk of the trees in which they were feeding in the manner of a Nuthatch Sitta europaea although they did not work the trunks in a Nuthatch like manner. Because of their colour and posture they reminded me just a little of Wallcreepers Tichodroma muraria (I wish!). Although we couldn't see what they feeding on we presumed feeding they were 'cus they were not gathering any material for any other purpose. One thing is for sure: they weren't extracting seeds.
Male Two-barred Crossbill Loxia leucoptera - Lynford Arboretum April 2014 Showing yellowish rump. Bird 1 clinging to the tree trunk and not really looking like a Wallcreeper at all!

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