It is possible to trace, in the flying equipment of birds, feathered versions of many of the refinements that render the modern aeroplane more efficient than its predecessors. It would, therefore, be a mistake to ignore birds as a guide to possible future developments. One of the most interesting groups of birds is that which includes all the owls, for there is a possible connection between the manner in which their strikingly silent flight is achieved and the increasingly pressing problem of silencing airscrews.