Terrestrial locomotion in penguins: it costs more to waddle.

@article{Pinshow1977TerrestrialLI,
  title={Terrestrial locomotion in penguins: it costs more to waddle.},
  author={Berry Pinshow and M. A. Fedak and Knut Schmidt-Nielsen},
  journal={Science},
  year={1977},
  volume={195 4278},
  pages={592-4}
}
The energetic cost for walking is relatively higher for penguins than for other birds or for quadrupeds of similar body mass. The morphology of penguins seems to represent a compromise between aquatic and terrestrial locomotion wherein both energy economy and speed suffer when the birds move on land.