WM Keck Science
Nitrogen and carbon isotope ratios were studied in a stratified deposit of guano of Mexican Free-tailed bats in Eagle Creek Cave, Arizona, U.S.A. Little diagenetic change was observed over the 25-year time span of the guano deposit. High aridity and reduced circulation of air in the cave are hypothesized to have slowed the normally rapid decomposition of the excreta and the subsequent escape of resultant ammonia. The results suggest the high dependency of the speed of diagenetic change on specific physical and other conditions of the caves and indicate that great care need be exercised in the interpretation of the isotopic ecogeochemistry of old guano. Relative contribution of C3 photosynthesis to the food chain leading to the bats was estimated to be more than C4 photosynthesis.
Mizutani, H., D.A. McFarlane, and Y. Kabaya. "Nitrogen and carbon isotope studies of a bat guano core from Eagle Creek Cave, Arizona, USA." Journal of the Mass Spectrometry Society of Japan 40.1 (1992): 57-65.