Using digital photography to study moult extent in breeding seabirds

Scoring moult from live birds in the hand takes time, thereby increasing the handling stress to the birds. We show that digital photography can be used to efficiently study moult extent across multiple feather tracts. We photographed the upper wings of incubating albatrosses and giant petrels to infer which remiges and greater secondary coverts had been replaced in the previous year. Wear contrasts differentiating ‘new’ from ‘old’ feathers were easier to see for dark than white feathers, and could be enhanced by increasing image saturation. Repeat photography of the same individuals in successive years showed that the inner secondaries and associated greater coverts wear faster than the central secondaries, and this needs to be considered when aging feathers of unknown birds. Scoring primary moult in the hand took more than twice as long as photographing the entire wing. There were a few discrepancies between moult scores from photographs and birds scored in the hand, mostly due to older feathers being scored as new. These errors likely resulted from rushing to score moult in the hand under indifferent lighting conditions. However, it is essential to ensure that the wing is fully spread, so that all feathers are visible. Photographing had no impact on hatching success and it is a useful and reliable method to study the extent and symmetry of moult.