88.2  Monday, Jan. 6 13:45  On transient-state ventilation of burrows with a single opening TURNER, JS*; PINSHOW, B; SUNY College of Environmental Science and Forestry; Ben-Gurion University of the Negev jsturner@syr.edu

Burrows provide shelter and accommodation for thousands of animal species, but they also can isolate their occupants from the atmosphere. If gas exchange between burrow and atmosphere is impeded, a burrow might become unsuitable for occupation. Standard models for gas exchange between burrows and atmosphere commonly invoke either diffusion, which is suitable only for exchange over distances that are smaller than the typical lengths of animal burrows; or bulk flow of air driven by winds, which requires that the burrow have at least two entrances. In Namibia, the burrow of the Cape skink, Trachylepis capensis, consists of a single vertical tunnel, 3-4 cm in diameter and 35-52 cm deep, which opens to the atmosphere through a single wide opening. We used laser-enhanced smoke visualization (LESV) to examine transient-state mechanisms for air exchange in these burrows. Capture of low-Reynolds number turbulent eddies, combined with probable viscous entrainment of burrow air, produces vigorous mixing of the upper air mass of the burrow, which facilitates mixing throughout the burrow. Clearance time constants were 30-40 s, and were commonly second-order, and in some instances, third order. In addition, the transient nature of eddy capture produced a sort of tidal ventilation in these burrows, with intermittent capture of eddies producing intermittent spurts of air exchange between the burrow and atmosphere. Our data support observations made by White et al. (1978 – Physiological Zoology 51:140-154) on European bee-eater nests, and we suggest that such transient-state air exchange may be a ubiquitous mechanism for gas exchange in burrows of all types.