Gas composition and its daily changes within burrows and nests of an Afroalpine fossorial rodent, the giant root-rat Tachyoryctes macrocephalus.

Fossorial mammals are supposed to face hypoxic and hypercapnic conditions, but such conditions have been rarely encountered in their natural burrow systems. Gas composition in burrows after heavy rains, deeper burrows and especially nest chambers, where animals usually spend most of the day, could be even more challenging than in shallow burrows. Such situations, however, have been rarely surveyed in the wild. In our study, we determined concentrations of O, CO and CH in active burrows and nests of the giant root-rat Tachyoryctes macrocephalus, a large fossorial rodent endemic to the Afroalpine zone of the Bale Mountains in Ethiopia. We were able to determine the precise location of nests by tracking individuals equipped with radio-collars. To the best of our knowledge, this is the first study that analyses air samples taken directly from the nests of actually occupied burrow systems in any free-living fossorial mammal. We found no evidence for environmental hypoxia in the examined burrows and nests (range 19.7-21.6% O). Concentrations of CO in the burrows increased after the burrows were plugged in the evening, but did not reach physiologically problematic levels. The highest CO concentrations in burrows were detected in the evening during a wet period (up to 0.44%). In root-rat nest chambers, the highest (but still harmless) CO concentrations (up to 1.31%) were detected in the morning (measured in the late dry season only) together with an elevated concentration (up to 13.5ppm) of CH. Regular surface activity of giant root-rats, combined with the relatively large dimensions of their nest chambers and tunnels, and the absence of heavy soils, may contribute to harmless atmospheres within their burrow systems.