Photography as an efficient tool to study moult
Published: 13 December 2016
Bird feathers fulfill several roles but must be in good condition to efficiently function. To maintain the feathers in a good state of repair birds regularly replace their old feathers with new ones during moult. This is a costly process and of interest to avian ecologists. To study moult, ornithologists needed to catch birds, but this may no longer necessary.
As the days get colder in the winter who does not love a cosy warm down jacket and duvet to keep warm. Providing fantastic insulation at a very light weight is just one of the roles bird feathers play. Feathers can come in many colours and bird either show off or blend into the background. And they are indispensable for flight. To fulfil their roles, feathers must be in good condition and to do this birds regularly replace their old feathers with new ones. This moult is a costly process and the questions of when and where a bird moults are important for understanding a species' ecology.
So, how do we know when birds moult? Traditionally we needed to catch birds, and while handling key feathers are scored as to whether they are moulting or not and at what stage of their moult they are. Catching birds is always time consuming and can be stressful for the bird. But that is not strictly necessary Bianca Vieira has spent plenty of time capture black skimmers only with her camera and here we show that we can use these photographs to score the moult of primary feathers from good-quality images.
Moulting feathers are recognisable by a difference in size when they are still growing and from their appearance once they are fully grown. We show that moulting primary feathers of Black Skimmers can be identified and scored reliably from photography of birds with spread-out wings. When the same observer scores the same picture twice the scores are very similar. Equally multiple observers' scores of the same images were also in close agreement with each other. This suggests that an image can provide information on the progress of moult, at least of primaries. Moreover, analysing a whole set of images from one season and site provided information on timing and duration of moult representative for this population. It should also be possible to score secondaries, possibly tertiaries and rectrices.
The photographic method works when birds can be readily photographed with at least one outstretched wing visible, typically in flight. Studying moult from images has many advantages. The bird does not need to be captured and handled thus would avoid the stress and potential risk of injuries associated with capture and handling. It can also be done on species that might be very difficult to catch but more easily photographed. With the widespread availability of good cameras and many observers taking excellent photographs this also gives the possibility to study moult over larger temporal and spatial scales than typically would possible for a research group through engaging the citizen into science.
Source: Bianca P Vieira, Robert W Furness adn Ruedi G Nager. In press. Using fiedl photography to study avian moult. Ibis
First published: 13 December 2016