Ageing and sexing Reed Bunting can be difficult when handling single birds. At a recent session on Chobham Common, where we caught 15 individuals, we had the opportunity to compare both males and females as well as different ages of birds too. Below is what we observed:
All photographs were taken on 5th October 2014 and are of four individuals (plus a fifth which better illustrated the alulae and primary coverts of a 1st autumn female).
The pattern of black and buff on crown feathers is straightforward at this time of year - the black base to the crown feathers in males is broad with 90%+ of the buff restricted to the feather tips. In females the black parts of the vanes form arrow-head
shapes with the buff extending down from the feather tip either side of the black.
Alulae and primary coverts
Ageing. The two males follow the literature: the adult has neatly rounded primary coverts whereas the young, while still rounded, are more loosely defined; both along their edges and around the tips. The females are harder to differentiate though the 1st Autumn bird does have greater wear than both adults.
Note that both adults exhibit dark outer alulae whereas both juveniles are paler. This isn't something I've read and we'll check future buntings as a follow-up. If anyone has a reference for this criteria do get in touch and I'll update this post.
Primary feather wear
Ageing. One has to look carefully to judge the amount of primary wear in Reed Bunting and even in October, a cursory look is often not enough. Compare the lower two birds with those above: the young male exhibits the most wear but the young female also has greater wear than both adults. Using the primaries for ageing gets progressively more difficult as the season progresses.
Tail shape and wear
Ageing. Reed Bunting have broad outer tail feather but it's the shape that can help age a bird. Adult tail feathers are rounded at the tip and, in October, generally show little wear. Juveniles are more pointed and a close inspection will show a greater degree of wear.