Moulting warblers in summer

Moulting adult Chiffchaff

Moulting Chiffchaff

During a ringing session on the Country Park this week, we encountered a number of recently-fledged young birds, and this is also the time that adults start to moult and renew their plumage. It was certainly the case with Chiffchaffs today – we trapped and ringed a few, and all but one were a newly-fledged youngsters. The remaining bird was an adult, which had already started to moult ready for its southbound migration.

As can be seen from the images, they become very scruffy and all the body, wings and tail start to be renewed. The image of the wing shows two brand new primary feathers in their waxy sheaths just starting to grow, whilst the tips of the old ones are worn and abraded (with just the feather shaft remaining).

Moulting Chiffchaff

Willow Warblers and Chiffchaffs carry out the same moult process at this time of year, and in the field this can cause an identification problem, especially if the bird doesn’t call.

The below image is of a bird from a few years ago which had lost all its tail (which can be seen growing) and was rapidly renewing its body feathers and some of the primaries. These species try and complete at least part of the moult before they make the long journey south for the winter.

Moulting Willow Warbler

Words and pictures by Peter J. Dunn