Future Aviary Design: The Science of Circular Flight Aviaries for Avian Welfare

Birds are kept in captive settings globally, and many of these birds are not flight-restrained. It is generally considered more ethical to house birds in aviaries than to practice flight restraint through wing clipping or pinioning, which means that aviaries are needed to prevent birds from escaping. Traditionally, rectangular aviaries are commonly used; these aviaries may not be well designed for bird flight, especially for large-bodied species. In this paper, we draw attention to the circular flight aviary, a design which has the potential to encourage extended flight in captive birds without the need for excessively large exhibit design. Several circular flight aviaries are already used in select zoos globally, but there is at present, limited empirical evidence on the welfare benefits for birds. We evaluate the tools that are required to assess the effects of circular flight aviary design on bird welfare, with a focus on aspects of exercise physiology that are sometimes overlooked in traditional welfare assessments. The circular design may also be used to overcome challenges associated with breeding birds in complex social structures, such as those which benefit from being housed in large flocks yet are intolerant of other individuals when nesting. Circular flight aviaries, if developed with a view to generating an evidence base, have the potential to improve bird welfare, at a time when bird flight is becoming more restricted globally due to disease implications.