Environmental information from guano palynology of insectivorous bats of the central part of the United States of America

Bat droppings accumulate in caves, and the resultant guano contains a stratigraphic record of the environment analogous to the record from lake sediment and peat. The bats forage at night for insects; they return to the cave during the day to sleep and care for their young. They attach themselves to suitable perches in the cave ceiling, and their excrement accumulates on the floor below. Flying requires a lot of energy, and bats of temperate regions consume large numbers of night-flying insects. In some situations the guano can reach a depth of meters in hundreds to thousands of years, and it has a valuable chronostratigraphy. The bat scats occur as small pellets that represent the non-digestible portion of the animal's diet in the preceding few hours; hence the diet provides information about the time of the year the feeding occurred. Bat guano contains, among other things, insect fragments, hair, pollen, and mineral matter. Night-flying insects do not normally visit flowers for the pollen; many species do not eat during the flying phase of their life cycle, and those that do generally are nectar feeders. Although the insects are not after the pollen, they do fly through a pollen-laden environment, and the pollen and dust adheres to their bodies. The insects essentially act as living traps for airborne debris. The bats also are furry pollen traps; during grooming they ingest pollen and dust enmeshed in their fur, and this also is excreted. The pollen in an individual scat contains a record of the atmospheric pollen during a single day in the past. This kind of detail is rarely available from lake sediment. Chemical analysis of individual bat scats in a time series can chart the changing environment caused by agriculture, industry, volcanic dust, and a host of other details that depend only on the cleverness of the researcher. Careful 14C analysis can isolate the times when bats did not use the cave, and that may be useful in interpreting past conditions. If the insect types in the guano change over time, that may provide evidence of changing climate. Pollen was analyzed from guano samples taken from Tumbling Creek Cave near Protem, Missouri, USA. The cave contains a maternal colony of the Grey Bat (Myotis grisescens) that occupies the cave for a short time each year. Scats collected from the base of a 70 cm thick cone of guano yielded an AMS 14C date of 2810 ± 40 yr BP. The fecal material has a crumbly structure below the surface; it was of mahogany color (7.5 YR 2/1 to 3/2) and had no noticeable odor. Guano can be processed like normal sediment, but simple washing in a weak detergent solution followed by acetolysis appears adequate.