Spring aging and the Titchwell bird
In the last few years, Iberian Chiffchaff has become an almost expected spring overshoot. In spring 2010, a singing bird was found at Titchwell RSPB, Norfolk. In spring 2011, an Iberian Chiffchaff was again present at Titchwell RSPB, reportedly singing from the same willows as the 2010 bird. Despite the recent increase in records, the species remains rare enough that the occurrence of a singing bird at the same site for two consecutive springs raised suspicions that it might be a returning bird.
Adult Iberian Chiffchaffs undergo a complete moult following breeding. By the following spring, their flight feathers are still in relatively good condition, fresh and black.
Adult Iberian Chiffchaff, Spain, April 2010 – Stephen Menzie (www.stephenmenzie.com)
Juveniles undergo a partial post-juvenile moult, which is more extensive than that of Common Chiffchaff and often includes some outer primaries. By the following spring, unmoulted juvenile primaries are worn and bleached; any moulted outer primaries are fresher and blacker, like adult primaries. The contrast between the two feather generations can be rather obvious.
‘First-summer’ Iberian Chiffchaff, Portugal, February 2011 – Peter Fearon (http://ascouseringer.blogspot.com). This bird has moulted the outer four primaries during its post-juvenile moult.
So, how does this help us with the Titchwell bird? Well, it’s a sad fact of life that no one stays young forever, and that goes for Iberian Chiffchaffs as well. This fantastic photo by Andy Thompson taken on 13th April 2011 answers the question of if the 2011 Titchwell bird was the same individual as was present in 2010. It shows a clear moult limit in the primaries, ageing it as a 2cy (‘1st summer’).
‘First-summer’ Iberian Chiffchaff, Titchwell RSPB, April 2011 – Andy Thompson (http://sites.google.com/site/wildaboutwildlife)
The bird has moulted the outer five primaries (arrowed). Notice how much blacker they are and less worn at the tips then the inner primaries, which are retained juvenile feathers. If this were the 2010 bird returning, it would be in adult plumage showing uniform adult-type primaries without any moult limit. So, we can say for sure that, as a 2cy, the 2011 bird is not the same individual as was present in 2010. Food for thought next time another rare vagrant ‘returns’!