External or implanted loggers?
During our fieldwork, we equipped red-throated divers with external as well as implanted loggers. The decision about which logger type to use for which animal depended, among other things, on whether the bird was moulting. In spring, divers moult from their wintering plumage into breeding plumage and external loggers which are attached to the feathers on the back would not last for long periods of time on moulting birds. Therefore, external loggers were only selected for divers that were already in breeding plumage with the distinctive red-brown throat patch.
Photo: A moulting red-throated diver. The breeding plumage is already clearly visible, but especially at the head and the throat you can still see that this animal is not yet completely moulted.