Clever mice

It turns out mice have a clever ability which has only just been discovered - the ability to sense oxygen levels through their nose: 

The genome of mice harbors more than 1000 odorant receptor genes, which enable them to smell myriad odors in their surroundings. Researchers ... have discovered that mice can also sense the oxygen level of the inhaled air using neurons in their nose. For this newly discovered sensory property, mice rely on two genes termed Gucy1b2 and Trpc2, but apparently not on odorant receptor genes.

The research team discovered that a specific type of chemosensory neuron in the mouse olfactory mucosa responds to oxygen decreases in the environment. Chemosensory cells typically detect an increase in the concentration of a substance. In mammals, a lack of oxygen was thought to be detected primarily by the carotid body, a sensory organ situated at the carotid arteries in the neck. Activation of the carotid body results in activation of the respiratory center in the brain. As mice live in burrows, it appears that during evolution an additional mechanism has developed in order to protect the individuals and their offspring from a shortage of oxygen....

Moreover, the scientists found that mice can learn very quickly where locations with low oxygen levels are, and then avoid these areas. By contrast, mice with inactivated Gucy1b2 or Trpc2 genes cannot distinguish between normal and modestly decreased oxygen levels in the external environment, and do not show avoidance behavior of these areas with a low oxygen level. These genes thus enable mice early on to select locations with an optimal oxygen level.