earlytorise
Well-known member
I am interested in this question, largely because I am researching the difference between Buteo japonicus and Buteo refectus.
Ebird mentions the more prominent dark trailing edge of the underwing of refectus as one separating feature. (The other feature is marginally darker trousers. I don't think that that can be verified confidently on a photo.)
But as I look through photos of japonicus on eBird, some individuals have a thicker dark trailing edge, some have a thinner dark one, and others have a trailing edge that looks dim but not actually dark.
As for photos of refectus, indeed most of these have a slightly thicker trailing edge than the japonicus with the thinner-looking dark trailing edge, but some other photos of refectus show a dim trailing edge.
What determines this? Is it age? Is it the moult within a year? Is it the plumage morph? Is it simply the light that goes through the feathers at the trailing edge, making them brighter on the photo?
In particular, can there be high variability in both the darkness and the width of the trailing edge of light-morph refectus? If so, this would mean that a vagrant japonicus that happened to turn up in the Himalayas might not be identifiable with good-quality photos, even if it had a thin dark trailing edge.
Thanks and cheers!
Ebird mentions the more prominent dark trailing edge of the underwing of refectus as one separating feature. (The other feature is marginally darker trousers. I don't think that that can be verified confidently on a photo.)
But as I look through photos of japonicus on eBird, some individuals have a thicker dark trailing edge, some have a thinner dark one, and others have a trailing edge that looks dim but not actually dark.
As for photos of refectus, indeed most of these have a slightly thicker trailing edge than the japonicus with the thinner-looking dark trailing edge, but some other photos of refectus show a dim trailing edge.
What determines this? Is it age? Is it the moult within a year? Is it the plumage morph? Is it simply the light that goes through the feathers at the trailing edge, making them brighter on the photo?
In particular, can there be high variability in both the darkness and the width of the trailing edge of light-morph refectus? If so, this would mean that a vagrant japonicus that happened to turn up in the Himalayas might not be identifiable with good-quality photos, even if it had a thin dark trailing edge.
Thanks and cheers!