citrinella
Well-known member
Hi Muso,
Apologies if you know all this already. I'll try and give a full explanation of why folk are ageing and sexing your bird as they are.
Puffed out and sleek are not necessarily related to age. Birds fluff up their feathers to improve insulation when it is cold, or when they feel cold !
Sexing reed buntings in winter plumage can be difficult. In breeding plumage adult Males have a black head. That is hidden in the winter - the new head feathers that grow in after post breeding moult have brown tips, which make the head appear brown. During the late winter and spring these brown tips wear off, revealing the black head. The speed and time this happens vary widely between individuals, so you can get males with brown heads surprisingly late. When we catch birds for ringing, we lift the crown feathers to look for the black underneath. There is another feature which you can sometimes see in the field. Males have a white collar round their nape, round the back of their neck. This often isn't very visible, and some females have a bit of white here too, so it isn't always easy to sex birds on that alone.
Ageing reed buntings late in the winter can be a nightmare - even in the hand it is often impossible. However, I too am pretty confident that the bird in your original photograph is _older_ than 1st calendar year. Adult birds moult post breeding. The new tail feathers they grow in are broad and round ended, like the ones in your original photos appear to me. Over time the feathers wear, fastest on the inside of the ends so that they become pointed, gradually getting sharper. They also become chipped - the tips look uneven, as in your photo.
Juvenile birds, which would be in their first calendar year in Feb/Mar, don't have a post breeding moult. Their feathers get badly worn across the side of the nest, so they look sharp pointed and chipped virtually from the start.
So early in the autumn it is relatively easy :
pointed tail - 1st calendar year;
rounded tail - 2nd calendar year or older, note that when folk say 2nd calendar year, they mean that - or older.
Then things start getting more difficult as adult tail feathers wear too. By the end of the winter reed bunting tails tend to have worn a lot, presumably due to the way they sit on the ground a lot to feed during winter. So adults can have very worn tails. The bird you photographed doesn't, it is actually unusually round for a reed bunting at this time of year, but not truly exceptional.
Wear is so common in adults in late winter and spring that, when ringing, we regard birds with worn tails at that time of year as being impossible to age.
There is one other complication ... sometimes birds lose their tails ! They then regrow a completely new tail, which looks very like a tail that has been grown following post breeding moult. Sometimes you can tell the difference. When a reed bunting (or other passerine) moults normally, they lose the feathers sequentially - one from each side at a time, and grow them in sequentially.
That means that the tail feathers are different lengths while they grow back in. When they lose the tail completely (or when chicks are growing their tails in the nest) all the feathers are growing at the same time. While growing their feathers, there may be a period when the bird doesn't get enough food, and that often shows in the tail feathers. In a tail that has been grown all at once, this "fault bar" as we call it, will go right across the tail in a straight line. If the tail has been grown during normal post-breeding moult it won't. So a bird with one or more fault bars going right across the tail cannot be aged reliably as 2nd cy or older, though it may be possible to age it as 1st cy.
I hope that gives an undertanding of why reed bunting often cannot be aged in late winter or spring
Mike.
P.S. Many passerines can be aged by looking for unmoulted greater coverts on similar principles. This does not work for reed buntings.
