Abstract
The flight of birds, especially over long distances, has recently come in for some attention. In some experiments, birds were set flying in a wind tunnel. By measuring their metabolism, the efficiency of their flight was studied. According to results, as might have been expected, flight is about the most efficient way of getting about, in terms of the number of calories of food energy needed to move a certain weight a certain distance. Apparently, swimming, however, can rival flying in efficiency in some cases. The whole article should be read.