Lesson in fault bars

In what turned out to be a quiet morning at Predannack, I thought we'd just post up a pic of this rather obvious set of fault bars on a Chaffinch.

Fault bars are areas of weakness where growing feathers have been compromised by poor weather, food shortage etc, and are normally most obvious on tail feathers. This can happen at any age, but the key thing to remember is that juveniles grow their main flight feathers (including tail) at the same time (in the nest), whereas adults will moult them sequentially. So although birds of any age can show fault bars, the fact that on this bird the distinct pattern of fault bars is the same distance from the tip of all the tail feathers indicates these were all grown at the same time; ie this is a juvenile bird.