Autumn movements (25 August 2004)

This is the time of year when we can see plumage changes in progress, and actually observe the process of moult, whereas at other times of year we can only use the results. For the benefit of our readers from overseas, I should perhaps explain that very few British ringers ever examine skull ossification, determining age on the moult and wear of plumage, shape of tail feathers and so on, and the coloration of bare parts for some species.

Whitethroat Sylvia communis is one of the warbler species in which the adults undergo their full moult here, fitting it in quickly between breeding and southward migration. After completion of the moult, the wings of adults look very fresh and quite similar to those of first-year birds. The shape and texture of the primary coverts is useful, but can be difficult to apply. The montage below shows (on the left) a first-year bird just finishing its post-juvenile moult of its median coverts, and (in the centre and on the right) two adults coming towards the end of their full moult, neither having any old feathers left and both actively moulting their outermost primaries and innermost secondaries. The difference in colour between the two adults is mainly a trick of the light, but they both show another interesting aspect of Whitethroats in the irregular moult of the secondaries. In both of these birds the innermost secondary, s6, next to the tertials, is almost fully grown and was moulted before the middle secondaries s4 and s5. Some Whitethroats have been reported to retain some old secondaries, and this is another feature that we should look out for.

Whitethroat is one of the passerines in which eye colour is quite helpful in ageing. The following composite image shows (top) a first-year bird (Euring age code 3) and (below) an adult bird (Euring age code 4). The adult bird has a paler, more reddish-brown iris than the muddy-grey-brown iris of the young bird. The species' white throat is often, as with these two, much cleaner and whiter in the adult, without the grey suffusion of the first-year bird. The adult bird is almost certainly a female, males usually being much greyer on the crown.

The tail shape and coloration can also be particularly helpful in ageing Whitethroats, provided that the usual care is taken not to be misled by first-year birds that have moulted some or all of their tail. First-year Whitethroats seem especially prone to growing new outermost tail feathers. Incorrect ageing can of course be avoided by not using any one character in isolation. The montage below shows three tails, photographed 15 or 19 August in Cheshire, from (left) a typical first-year bird, (centre) a first-year bird with an unusual amount of white in t5 and t6 (the outermost two feathers on both sides), and (right) an adult bird towards the end of its full moult (t4, t5 and t6 had not quite finished growing, and t4 on its left side - the right side of the photo - is hidden). Again, the colour balance is affected by the sunlight and the colours are not wholly accurate, but the generally more grey tone of the adult is correct, and especially the amount and extent of the pure white on the outer rectrices is the key feature. These pages have illustrated some of these points before.

Great Spotted Woodpecker Dendrocopos major juvenile birds have a red crown (the top of the head), not to be confused with the red nape (back of the neck) that male birds have:

The iris is brown, and becomes red with age, as shown previously in these pages. Juvenile birds undergo a full moult of all of their primary feathers, but not the corresponding primary coverts:

Juvenile primary feathers have an off-white spot at the tip which is absent in the 'adult' type primary feathers grown in the post-juvenile moult, but this feature is not particularly helpful in ageing, as all birds with 'white-tipped' primaries also have at least some of the red crown feathers, which is a pretty obvious give-away for a juvenile bird.

Adult birds moult primaries as well, of course, but they also moult secondaries, tertials, tail and indeed most of their feathers (but not usually all of them, as the moult of older woodpeckers is complex). The possible confusion in ageing comes later in the year when the juveniles have finished their post-juvenile moult, lost all the red on the crown, and finished moulting their primaries. As shown in the picture at the left, moult of the primary feathers without the corresponding primary coverts is a characteristic feature by which woodpeckers can be aged at other times of year. The same also applies to the North American species such as Downy Picoides pubescens and Hairy Picoides villosus Woodpeckers, and Northern Flickers Colaptes auratus.

These pages have previously carried extensive articles on moult in first-year finches, including Greenfinches Carduelis chloris where about one-in-ten birds in winter 2003/ 04 had moulted one or more primary feathers. Now is the time of year when the first-year birds are actively moulting and is the ideal time to see the progress of any eccentric moult. I ring few Greenfinches outside the winter period, but have recently caught 53 birds from a flock of Goldfinches Carduelis carduelis, nine adults and 44 juveniles, in which one juvenile bird was moulting four primary feathers, pp3, 4, 5 and 6 (counting from the inside, as is usual in moult studies). Primaries 3 and 4 were fully grown, recently moulted, and primaries 5 and 6 were still growing on 19 August:

This was an unusual bird in another way because it had a somewhat deformed bill, curving downwards and with an extended lower mandible (left photo below), contrasting with the normal juvenile at the right:

A young Linnet Carduelis cannabina accompanying the Goldfinch flock also had feathers still growing, but in this case it was because it was so recently fledged that it was still not fully grown: a 1J in Euring code, known as 'Local' to North American banders. Even at this age, many birds are sexable on the basis of the amount of white on the primaries; this bird has white almost to the feather-vane and is a male. The photograph of the underwing shows the growing feathers still emerging from their pins, and the underwing coverts just starting to grow:

David Norman.