I visited quickly Finnish Museum of Natural History to check all Red-flanked Bluetail skins they have. I'm interested to see if there are some plumage details that make ageing of autumn birds reliable. Many times you can see ageing done mostly basing on the shape of tail feathers and I'm not sure if it is a reliable character always. One thing that I'm interested are tertials, but I have to see more individuals. So, I'm heading for Tring museum tomorrow and I hope I have more knowledge after that.
Autumn birds. Compare the shape of R1 between age classes. Left adult female, middle first-winter, right juvenile. It seems that this juvenile bird has clearly broader R1 than adult female. Also the tip of R1 is more rounded in juvenile bird. That's the reason for not ageing autumn Red-flanked Bluetails in field basing on the shape of Rs. © Finnish Museum of Natural History
