Hillwell, Shetland, Sept- Oct 2011
An earlier post about the juvenile Pallid Harrier, produce very interesting responses and questions. Roger Riddington has replied in detail to this question from JanJ, repeated here. Good learning!
Interesting bird – the Fulmar-oiled Hillwell harrier!
Apart from the features mentioned and given the quality of the pic I find it rather difficult to identify it for certain – both as a Pallid or a Montagu´s, since the various pic provide different impressions of structure. One important reason for this is the obvious notched p7, which would be very odd for both Pallid and Montagu´s. It is however, the rule for Hen. Further on it shares the wing-formula – shorter p10 which is approx. as long as p5, with Hen, usually approx as long as p6 in Montagu´s. It might be reasonable to consider a hybrid Pallid x Hen.
Some interesting potential hybrids from this autumn.
Thanks for your comments, and the links to some really interesting (=scary) harriers on netfugl.dk. You’re quite right that a hybrid ought to be considered when trying to work out what the Hillwell harrier is, and my very hastily prepared summary for Martin really only covered my reasons for thinking that the bird is a Pallid rather than a Monty’s. The discussion on this thread (http://tinyurl.com/5tzpcxz), together with your comments about wing structure, prompted me to take a closer look at the Hillwell bird’s wings. (An over-riding caveat is that the bird is badly oiled and therefore it’s not as easy as it might otherwise be.) You comment that there is a notch on P7 (the fourth finger from the edge of the wing), but I’m not sure I can see a notch on P7 in any of the pics posted on the site. In a few shots, P6 is ‘stuck’ to P7 (an effect of the fulmar oil), perhaps giving the impression of a notch (eg pics a & c, plus Ian Cowgill’s pic). Ian’s photo, which is the best I’ve seen so far, allows a closer assessment of some aspects of wing formula – see pic below. So, from the outside, P10 (outermost) is completely emarginated; the visible part of P9 (i.e. at least as far as the primary coverts) is completely emarginated; on P8 the emargination stretches over halfway between the tip of the primary and the primary covert tip; on P7 (tip broken off) the emargination stretches roughly halfway between the primary tip and the primary coverts; P6 is not emarginated (note that P5 is stuck to P6, creating the gap in the wing). P10 is clearly shorter than P6 and, as best as I can judge it, lies between P6 and P5 (eg photo a and Ian’s pic). So, what does all that tell us? The lack of emargination on P6 rules out a (pure) Hen Harrier. Not sure it rules out a Hen x Pallid, although Dick Forsman used the presence of an emarginated P6 as one factor to point to a hybrid origin for the bird discussed in the link above. According to the diagram of wing formula of the three European spp in Hollom (1960), everything is ok for Pallid in terms of emarginations, but in Monty’s the emargination of P9 normally stops short of the primary coverts (i.e. the ‘step’ is usually visible), whereas in the Hillwell bird the whole of the visible primary is emarginated. In terms of length of P10, there is more variation between the species, or rather it’s hard to be absolute when examining the feature on a spread wind in the field rather than measuring a specimen or a live bird in the hand – but I can’t see that the length and relative position of P10 is wrong for Pallid. I do think this is a really difficult bird by the way, so I’m not dogmatic about my conclusion that the most parsimonious explanation is a juv Pallid (and I hope we will not need dna to nail it!). But as far as I can tell, wing structure is better for Pallid than any other option – ?