Thursday, 15 September 2011

Swallows moult and ageing

Recently I have been working on a swallow roost once or twice every week. I enjoy ringing at night, and swallow are nice birds to ring. Most birds are Barn Swallow and Sand Martin, but also few Red-rumped Swallow. The adult of these species perform a complete moult on their African wintering grounds. Before autumn migrations the adults perform a partial or suspended moult: Barn Swallow - most partial and a few suspended and Sand Martin - most suspended. The partial moult includes, normally, a few wing coverts, tertials and body feathers; the suspended moult includes additionally a few innermost primaries.
In spring migration, after the complete moult these species' age cannot be determined, as all birds have fresh plumage.
In Israel, our local Barn Swallow population ('transitiva' type) perform complete moult after breeding season. This may complicate determining the age correctly when young birds with active post-juvenile moult can be mistaken with adults during their post-breeding moult.
Thanks to Hans-Jorgen Eilts for the interesting discussion about this moult.

Barn Swallow - adult - suspended moult, P1-2 fresh

Sand Martin - adult - suspended moult, P1-2 fresh

Sand Martin - juvenile, all plumage fresh with white edges

Yellow Wagtail

Last roost catch