@article{Schmaljohann-2009-5673,
  author = {Schmaljohann, H and Liechti, F},
  title = {Adjustments of Wingbeat Frequency and Air Speed to Air Density in Free-Flying Migratory Birds},
  journal = {Journal of Experimental Biology},
  year = {2009},
  month = {aug},
  publisher = {The Company of Biologists},
  volume = {212},
  pages = {3633--3642},
  doi = {10.1242/jeb.031435},
  url = {http://jeb.biologists.org/content/212/22/3633},
  keywords = {Birds},
}