Signs of Spring (29 March 2010)
Spring is on its way, not just because of British Summer Time, but the birds know it!
At my final 'winter season' visit to a local (north Cheshire) woodland site on 28 March, the first birds caught were two male Chiffchaffs Phylloscopus collybita. Not all Chiffchaffs are easy to age, but these two made a nice comparison with one an 'adult', hatched in 2008 or before (Euring age 6) and the other a 'second-year', hatched in 2009 (Euring age code 5). The adult is on the left in the attached images, with a broad and rounded tail, not very worn, and relatively fresh primary tips compared with the narrow, abraded tail and worn primaries of the first-year bird (especially the more bleached and exposed primary tips). Of course we have to beware of the occasional bird that might have moulted its tail, but the combination of characters is diagnostic. Interestingly, the adult bird here has accidentally replaced one tail feather, r3 on the right-hand side of its tail, which shows a darker and somewhat more glossy texture, but also has very obvious daily growth bars, clearly different from its other eleven rectrices.
A moult limit can sometimes be seen in the greater coverts, young birds in their post-juvenile moult typically retaining four old greater coverts (ogcs), but I find that difficult to see on many birds in spring. Some birds have a partial pre-breeding moult, especially of one or more tertial feathers and perhaps the central tail feathers, but these are irrelevant for ageing.
Another example of a spring adult Chiffchaff, from the same site, was on these pages seven years ago.
Addendum (3 April 2010):
Amongst the Chiffchaffs caught on 3 April 2010 at Oxmoor Local Nature Reserve, Runcorn, Cheshire, one provided some interesting additional features to those depicted above. This is another 'second-year' bird (age 5, hatched 2009) that had renewed its longest tertial (s7) and, at first glance, also appeared to have an adult-type tail.
A close-up of its wing shows the worn primaries, similar to those of the right-hand bird above, its fresh longest tertial, presumably grown in its winter quarters a month or two ago, an unusually distinct moult limit in the greater coverts, with four ogcs, and what appear to be some old (juvenile, grown in the nest) median and lesser coverts as well. Finally, the primary coverts of this individual are very pointed and frayed, also typical of an age-5 bird.
On closer inspection of its tail, all of the feathers were adult-type, rounded and relatively unabraded, apart from the outermost feather on each side. From the state of the adult-type feathers, which appear to be about as worn as those of a typical adult bird, I suspect that they were grown last autumn and are now just over six months old and have several thousand miles 'on the clock', having served the bird for its migration to and from the Mediterranean basin, or farther.
As usual, a combination of as many characteristics as possible should be used to help in deciding on a bird's age.
Two male Chaffinches Fringilla coelebs caught together on 13 March also made a nice comparison. This is one of the species that gains its breeding plumage by abrasion of the lighter-coloured tips of the small feathers of the head and elsewhere, as also commented previously on these pages. Their bills also become blue as the breeding hormones start to circulate. It is interesting that the 'second-year' male (hatched in 2009, Euring age code 5) (the upper bird in the image below, with pointed and worn tail feathers, abraded tertials and slightly worn primaries) showed much brighter colours, and a bluer bill, than the adult bird (the lower image in the image, with rounded and quite fresh tail feathers, relatively unworn tertials, notably fringed, and with virtually unabraded primaries); my expectation would be that an experienced adult bird would reach breeding condition before a second-year individual. I think the reason for this contrary example is that the second-year male, with a wing of 86.5 mm and weight of 22.5 g, is a local bird while the adult, with a wing of 92.0 mm and weight of 24.7 g, is clearly of Scandinavian stock and will have to migrate first and start its breeding season later.
Another species showing similar effects, with the tips wearing off winter plumage and the bill changing colour, is Starling Sturnus vulgaris. The distal (outer) part of the bill becomes bright yellow and the proximal (inner) part, mainly of the lower mandible, is pink for a female and blue for a male, easy to remember as it is the same as the human convention for girls and boys. The two below, ringed on 19 March, show the bill colour rather nicely, and the female also shows the white ring towards the outside of her iris.
This female does not look as glossy as the male, probably because she is a first-year bird (Euring age 5) while the male is an adult (Euring age 6), fairly readily determined by the pointedness of feathers on the uppertail coverts (as depicted previously), and the tail (second-year female on the left, adult male on the right in the image below). The fact that their bills are almost equally bright could be explained because female Starlings breed at one year of age, while many males do not; some second-year males do not exhibit much of a blue bill.