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VOLUME 24, NO. 4 Winter 2006


The Lure of Dirt
Peruvian fruit bats gather
Adriana Bravo

In the Amazonian forests of southeastern Peru, a diverse collection of animals regularly visits bare-earth clearings called clay licks or collpas for the express purpose of eating the exposed dirt. Monkeys, tapirs, deer, peccaries, rodents and birds frequent the sites. In addition, hundreds of fruit bats of nearly two dozen species congregate at collpas each night to drink the mineral-rich water that collects there.
 
My research, supported by a Bat Conservation International Student Research Scholarship, strongly suggests that the collpas are a key resource for Peruvian fruit bats and should be high-priority targets for conservation, since fruit bats are essential to tropical rain forests. As primary seed-dispersers for many plants, bats are essential for maintaining the diversity that is vital to the forest ecosystem.
 
Consuming soil, a practice known as geophagy, is widespread among mammals that primarily eat fruit, but it is not fully understood. The animals are believed to use earth as a source of important minerals that are largely missing from their fruit diet. Even less is known about why bats drink collpa water and the implications of this behavior.
 
My research focused on three major collpas in Peru’s Los Amigos Conservation Concession, a privately operated reserve that protects 525 square miles (136,000 hectares) of pristine Amazonian forest. Several field assistants and I captured bats once a week with mist nets at the three collpas and at three sites in the surrounding forest. One net was placed at each collpa and 6 to 10 nets at each forest site. For comparisons, we calculated a capture ratio (bats per net hour) for each site.
 
The collpa nets kept us busy, averaging just over 10 captured bats per hour. The forest nets produced barely a tenth as much: less then one bat per net hour. Bats clearly were drawn to the muddy puddles.
 
We identified 25 species of bats captured at the collpas, the most common of which was Heller’s broad-nosed bat (Platyrrhinus helleri). Only two of the 25 species were non-fruit bats, each represented by a single individual. Nets placed in the forests produced 18 species, including only 11 fruit bats. Our capture results strongly support the hypothesis that fruit bats visit collpas more than nectar- and insect-eating bats, although the reasons for this difference remain unconfirmed.
 
Hints of a possible explanation, however, may be found in the gender differences we discovered. In the forests, we captured roughly four female bats for every five males. By contrast, seven out of every ten bats captured at the collpas were female – and 80 percent of the captured females were either pregnant or lactating. The gender difference implies that collpas may be offering essential nutrients that are missing from the fruit diets of these female bats. Other researchers have shown that nursing female fruit bats face nutritional shortcomings, and some species of fruit-eating bats are reported to supplement their diets with leaves, flower parts, nectar, pollen and insects. Water at the collpas may contain nutrients that help the bats overcome dietary limitations.
 
Calcium has been proposed as an especially important missing nutrient for lactating bats, and researchers in Colorado report concentrations of female insect-eating bats visiting calcium-rich water holes. Further research is needed to confirm this hypothesis and to answer many other questions about bats’ use of the collpas and their importance in maintaining healthy populations of bats and other wildlife. I hope to resolve some of those issues with further research in the Los Amigos Conservation Concession.
 
Nonetheless, this study – the first to examine the relationship between collpas and frugivorous bats in the Peruvian Amazon – is an important first step toward demonstrating the importance of conserving collpas as critical resources for bats.
 
In 2001, the Peruvian government signed an agreement with the Amazon Conservation Association to create the nation’s first private conservation concession to protect the Los Amigos River watershed. About 30 collpas have been identified within the concession. However, this effort has not been enough to fully protect this invaluable habitat from degradation. Outside protected areas, and sometimes even within them, collpas are being strongly disturbed by illegal hunters. Tapirs, deer and peccaries visit the clay pits regularly, becoming easy prey in the open areas. Other potential threats include gold mining and illegal logging.
 
At the conclusion of this study, I should be able to recommend to government agencies and conservation groups appropriate actions for conserving these vital natural resources, as well as solid justifications for doing so. The long-term health of the rain forest ecosystem depends on the bats that drink the mineral-rich waters. 
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ADRIANA BRAVO is working toward a Ph.D. in biology at Louisiana State University in Baton Rouge. Acknowledgments This research is largely due to the dedication of Colin O’Donnell and Jane Sedgely of the New Zealand Department of Conservation. (They both completed their Ph.D.s on bats during this project.) The fieldwork involved many people over a decade and beyond, particularly B. Ebert, B. Lawrence, M. Lettink, C. Ryan and W. Simpson. Richard Barker and Ian Westbrooke provided statistical advice and analysis. The author also thanks Annette Hamblett and Lynette Hartley for their invaluable comments.

 
All articles in this issue:
The Passing of Friends
The Lure of Dirt
A New World Record
A Treasure Trove of Fruit Bats
Stoats, Rats & Bats
Entertaining Education
Bats: The Fight for Flight
The Perils of Glue Traps

Unless otherwise noted, all images are copyright ©Merlin D. Tuttle and/or ©Bat Conservation International