Figure 2.

Acoustic properties of Onychomys long-distance calls produced in normal air (‘air 1’, in home cage; ‘air 2’ in experimental cage) and heliox. (a) Centroid fundamental frequency (F₀) of long-distance calls in air and heliox. Fundamental frequency was slightly higher in heliox but remained far below the predicted frequency estimated from the frequency response of a whistle (‘expected in heliox’; see Material and methods). (b) Duration of long-distance calls produced in air and heliox. Relative level (dB) of the second (c) and third (d) harmonics of long-distance calls in air and heliox. Error bars indicate mean ± s.d. for individual mice. Home cage recordings were not available for TNK03A.