Assessing the use of digital photographs for the determination of duck species, age and sex

Wing surveys are an important tool for understanding harvest and can provide information on productivity and survival which can complement traditional methods (such as ringing). However, storing and collecting wings at a national level is challenging and costly and limits hunter participation in such schemes. Digital photographs of wings offer an alternative method of capturing this data from hunting bags, but the accuracy and suitability of this method have not previously been adequately assessed. To investigate the accuracy of species, age and sex determinations from digital photographs of wings, we sent 97 photographs of wings which had been determined in hand to experienced duck ringers. Photographs were chosen of the three most commonly hunted duck species in the UK (mallard, teal and wigeon) and represented a range of lighting and feather quality. The accuracy of species (mallard 99.8%, teal, 99.4%, wigeon 98.6%) and sex (mallard 86.3%, teal, 80.6%, wigeon, 90.0%) determination was high. However, the proportion of wings with correctly assigned species, age and sex was low for mallard (50.3%) and teal (48.8%) and moderate for wigeon (79.7%). Our results support the use of digital photographs for the determination of species and sex for these species. However, further work is required to identify the factors which could increase the successful determination of characteristics, especially age, from photos alone. We suggest that further work exploring the use of photographs of the entire bird or specific features is likely to find higher determination accuracies, albeit at a potential cost to hunter recruitment.