Extreme lightweight structures: avian feathers and bones

Flight is not the exclusive domain of birds; mammals (bats), insects, and some fish have independently developed this ability by the process of convergent evolution. Birds, however, greatly outperform other flying animals in efficiency and duration; for example the common swift (Apus apus) has recently been reported to regularly fly for periods of 10 months during migration. Birds owe this extraordinary capability to feathers and bones, which...