The direction and range of ambient temperature change influences yawning in budgerigars (Melopsittacus undulatus)
Journal of Comparative Psychology (2010) - Comment
pubmed: 20476812  doi: 10.1037/a0018006  issn: 1939-2087  issn: 0735-7036 

Andrew C. Gallup, Michael L. Miller, Anne B. Clark