Wednesday, 18 April 2012

Ageing Chiffchaffs in Spring

This weekend I re-trapped a Chiffchaff that I had originally captured at Botley Wood in April 2011, giving me the ideal opportunity to test my ageing skills on a spring bird. Published literature, including my trusty Svensson and Jenni and Winkler, suggest that it is possible to age spring birds due to the extent of wear on primary and tail feathers, and on the presence of contrast in the wing feathers. Although Svensson does warn that the flight feathers of the nominate subspecies Phylloscopus collybita collybita "on average appear to wear more" than those of the subspecies P.c. albietinus.

So armed with these facts, and knowing that this bird was ringed on 3rd April 2011, and therefore was definitely an adult bird, I set about my task. Svensson states that in spring adult birds have all wing feathers the same generation, the tips of the primary feathers still well kept and the tail feathers dark grey and glossy. In addition, the primary coverts are neatly edged greenish. In 2nd year birds though, there is often a contrast between moulted adult central tail feathers and rest of tail and both the tips of the primaries and tail feathers are worn. In addition there is sometimes a contrast between slightly duller and greyish greater coverts.

Adult Chiff Wing Feathers

The first thing to notice with this bird was the extent of wear on the tips of the primaries, particularly primaries four and five (the third and fourth from the top), and also the extent of bleaching where feathers have overlaid each other.

Tail of Adult Chiff Tail

The second thing to notice was the extent of wear at the tips of the tail, and interestingly the difference between the left and right side of the tail. The right side (top) is broad and rounded and in good condition, as would be expected in an adult, whereas the left side (lower) is more abraded, with the feathers appearing thinner and more pointed and browner, as would be expected with a 2nd year.

Greater Coverts of Adult Chiff

Finally, the greater coverts should appear uniform and all of the same generation in an adult bird, but interestingly the colouration of the fringing and the extent of wear on this bird seems to indicate two generations of feathers, although the ground colour of the each and their length, would tend to suggest that they are all the same age.

The moult strategy of adult Chiffchaffs is relatively straight forward, with a complete moult carried out post breeding, and a partial moult carried out on the wintering grounds, and yet the condition of the wing and tail feathers on this bird would tend to indicate a 2nd year bird. This bird could have lost half of its tail during migration or on its wintering grounds which would explain the difference there, but the extent of wear on the primaries seemed extensive for an adult bird. Svensson does warn that ageing on wear alone can be complicated due to the nominate race collybita returning from its wintering ground with more worn flight feathers, and I guess this bird is proof of that.


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