The recognition of individual animals is essential for many types of ecological research, as it enables estimates of demographic parameters such as population size, survival and reproductive rates. A popular method of visually identifying individuals uses natural variations in spot, stripe or scar markings. Although several studies have assessed the accuracy of these methods in mammals, crustaceans and fish, there have been few attempts to determine whether phenotypic characteristics are accurate when used for birds. Furthermore, even less is known about whether shed or moulted body parts can be reliably used to visually identify individuals. Here we assessed the accuracy of using phenotypic characteristics to identify avian individuals using a double-marking experiment, whereby nine microsatellite genetic markers and natural markings on shed feathers were used to independently identify northern goshawks Accipiter gentilis. Phenotypic and genetic identification of individuals was consistent in 94.4% (51/54) comparisons. Our results suggest that the phenotypic characteristics of shed feathers can be reliably used as a non-invasive and relatively inexpensive technique to monitor populations of an elusive species, the northern goshawk, without having to physically re-capture or re-sight individuals. We posit that using natural markings on shed feathers will also be a reliable method of identifying individuals in avian species with similar phenotypic characteristics, such as other Accipiter species.
We are grateful to S. Piertney for allowing access to laboratory facilities and to M. Wenzel, R. Ogden and G. Murray-Dickson for their advice on genetic methods. This research was partly funded by a Natural Environment Research Council studentship NE/J500148/1 to SH and by Natural Research Limited.