The 2011 IgNobel price in physiology has been awarded to a group for their paper
Wilkinson, A., N. Sebanz, I. Mandl, and L. Huber. “No Evidence of Contagious Yawning in the Red-footed Tortoise Geochelone Carbonaria.” Curr Zool 57, no. 4 (2011): 477–484.
It is freely available on the web: http://www.currentzoology.org/paperdetail.asp?id=11922
They have a nice summary of the current state of affairs. While contagious yawning is known to occur in some species, the reason for it is still not understood. There are several hypotheses to explain contagious yawning in humans, and each hypothesis makes a different prediction for what other animals should experience contagious yawning:
- One hypothesis states that "yawning is a fixed action pattern for which the releaser stimulus is the observation of another yawn". This hypothesis would predict that contagious yawning should be observed in all vertebrates that yawn.
- Another hypothesis states that this is an act of "non-concious social mimicry", in which case it should be observed in those species where "perception and action rely on common neural representations and social relations are of import".
- Yet a third hypothesis relates contagious yawning to empathy, in which case only the higher primates should show it.
Aim of the study was to find an animal that does not show empathy or non-social mimicry and see if that species showed contagious yawning. If so, it would support the first hypothesis, if not, it would rule it out.
The result of their paper:
The results revealed that there was no overall difference in responding across conditions suggesting that tortoises do not possess the ability to yawn contagiously
So we have at least one species that yawns, but doesn't yawn contagiously.