Responses of Common Tern Chicks to feather sample removal

Feather sampling is often assumed to be harmless, but this assumption has not been tested. From 2008–2012, we recorded the behavior of 340 Common Tern (Sterna hirundo) chicks following the removal of a pinch of body feathers. Only 11.2% of these chicks ran after sampling and 69.4% showed no visible reaction to sampling. The probability of a chick running away increased with age. We therefore recommend that sampling be conducted as soon as possible after juvenal feathers emerge. There was evidence for individual differences in behavior: approximately 71% of chicks that ran after feather sampling also ran away when re-encountered on later dates, while other chicks rarely did so. We found no evidence that removal of feather samples increased chick mortality, supporting the assumption that this technique is minimally invasive, but small differences in mortality rates would have been difficult to detect.