Claw colour in Pied Flycatcher Ficedula hypoleuca nestlings – an improved method of judging readiness for ringing

Claw darkening is a useful sign that Pied Flycatcher Ficedula hypoleuca nestlings are large enough to ring with a British Trust for Ornithology ring size A (internal diameter 2.3 mm), accurately predicting that 99.9% of nestlings can be ringed safely, compared to 99.8% for primary-feather development of ‘feathers short’ and 94.6% for age of five or more days. All Pied Flycatcher nestlings that had dark grey claws and had reached at least the ‘in-pin’ stage of primary-feather development were of a suitable size for ringing.