CiteSeerX 10.1.1.115.1294. doi:10.1023/A:1011695406277. S2CID 951896. ↑ Elliott, Kyle H.; Ricklefs, Robert E.; Gaston, Anthony J.; Hatch, Scott A.; Speakman, John R.; Davoren, Gail K. (2013). "High flight costs, but low dive costs, in auks support the biomechanical hypothesis for flightlessness in penguins".