Atmospheric Conditions in Artificial Rodent Burrows

Abstract

Rodents alter the atmospheric conditions in artificial burrows by lowering the partial pressure of oxygen by 10-15 mm Hg and increasing carbon dioxide levels to 0.5-1.5 volumes %. Condensed water is present in the burrows at all times independent of outside humidity. Ammonia levels did not rise above 100 parts per million because the rodents defecated and probably urinated above ground in this system. Presence of a rodent in the burrow does not significantly affect its temperature. Artificial burrows of nocturnal rodents exhibit greater temperature fluctuation than those of diurnal rodents. Burrow temperatures of nocturnal rodents average higher than those of diurnal rodents. Presence of more than one rodent in a single burrow magnifies the drop in oxygen and rise in carbon dioxide as does prolonged rain. Kennerly (1964) and McNab (1966) have reported quite complete studies of the atmospheric conditions existing in the burrows of pocket gophers and have reviewed the literature existing prior to their findings. Hayward (1966) reported that one or more rabbits in a burrow have a definite affect on respiratory gases. This somewhat limited data concerning atmospheric conditions is understandable in view of the difficulty of collecting samples from most natural rodent burrows. The present study reports the manner in which rodents affect environmental conditions in an artificial system and a comparison of this data with that reported for natural burrows. MATERIALS AND METHODS. Artificial burrows were constructed of 1/4 inch mesh hardware cloth covered with a layer of cheesecloth to prevent soil from filtering into the burrow. Each of the six burrows consisted of a single tunnel about 3 inches in diameter leading obliquely into the soil to a depth of about 7 inches followed by a horizontal portion of tunnel and ending blindly in a cylindrical nest area 6 inches in diameter by 7 inches in length (volume about 3L). Total length from mouth of tunnel to end of nesting chamber was about 3 feet. Burrows were buried in a 4 x 4 x 2 foot wooden box. Tunnels were 1 This study was supported in part by PHS Grant GM 14251-01 and the Institute of Scientific Research, New Mexico Highlands University.