Quote:
Original posted by brendank at 1/03/2013 23:46 
Alström & Olsson, 1999, suggest that Bianchi's Warbler completely lacks a wingbar in <10% of birds. This bird clearly lacks a wingbar, as did the bird at Aberdeen Reservoir and also the one I saw at LFS in January. The bird at Pak Sha O also seemed to lake a wingbar during my brief views of it. The probability of observing four such Bianchi's Warbler without a wingbar is 0.01% assuming only 10% lack a wingbar suggesting that at least some aren't Bianchi's Warbler
But the combined probability cannot be applied to any single individual - the probability for each individual Bianchi's lacking a wing bar remains 10%, regardless of whether other birds seen in the same area also lack a wing bar. Thus for assessing each individual, this feature cannot be used as 'proof' that the bird is not Bianchi's. In fact, it is plausible that the probability changes across the range of the species, and/or is affected by the age of the bird or wear of the feather. Thus for example a fresh-plumaged Bianchi's in Sichuan may have a 10% chance of lacking a wing bar, but a late winter Bianchi's in Hong Kong may have a higher or lower chance (do we know?). Two-barred Warbler has two clear wing bars in the autumn, but these can fade to almost nothing by the following spring (at least, this appears to have happened on the bird that overwintered at Mai Po last year).
I saw a Bianchi's earlier this winter (December) which more or less completely lacked a wing bar. Fortunately it was calling, and the call matched those recordings of Bianchi's on Xeno-canto, and did not match recordings of Martens'. As others have said, the call may be crucial in ID of these species.
[
Last edited by ajohn at 2/03/2013 08:59 ]
