Spatial and temporal expression of vegetation and atmospheric variability from stable carbon and nitrogen isotope analysis of bat guano in the southern United States

Stable isotopes of faeces contain information related to the animals feeding ecology. The use of stable isotope values from subfossil faeces as a palaeoenvironmental indicator depends on how faithfully the animal records their local environment. Here we present insectivorous bat guano delta C-13 and delta N-15 values from a precipitation gradient across the southern United States and northern Mexico to compare with local vegetation and climate. We find delta C-13 values to be an excellent predictor of expected C-4/CAM vegetation, indicating that the bats are non-selective in their diet. Moreover, we find bat guano delta C-13 values to be strongly correlated with summer precipitation amount and winter precipitation ratio. We also find evidence for a significant relationship with mean annual temperature. In general, we do not find delta N-15 values to be related to any parameters along the climatic gradient we examined. Additionally, we measured delta C-13 and delta N-15 values of bulk guano deposited annually from 1968 to 1987 in a varved guano deposit at Eagle Creek Cave, Arizona. Neither delta C-13 nor delta N-15 values were significantly related to various local meteorological variables; however, we found delta C-13 values of guano to be significantly related to drought and to the North American Monsoon indicating bat guano delta C-13 values preserve an interpretable record of large-scale atmospheric variability. (c) 2007 Elsevier Ltd. All rights reserved.