Bats at clay licks.
Alan Lee
Amazingly, having never read about bats at clay licks, within the last 2 months there have been two publications on the topic from South America - one from Ecuador and one from Peru. The latter is by Adriana Bravo, who used to work at TRC as a guide and on the macaw project. She is currently doing her doctorate at Louisiana State University. Interestingly, the findings are very similar, but conclusions a bit different as we shall see.
Many animals in the tropics of Africa, Asia and South America regularly visit so-called salt or mineral licks to consume clay or drink clay-saturated water. Whether this behavior is used to supplement diets with locally limited nutrients or to buffer the effects of toxic secondary plant compounds remains unclear. We now know that in the Amazonian rainforest, pregnant and lactating bats are frequently observed and captured at mineral licks. The study in Ecuador measured the nitrogen isotope ratio in wing tissue of omnivorous short-tailed fruit bats, Carollia perspicillata, and in an obligate fruit-eating bat, Artibeus obscurus, captured at mineral licks and at control sites in the rainforest. Carollia perspicillata with a plant-dominated diet were more often captured at mineral licks than individuals with an insect-dominated diet, although insects were more mineral depleted than fruits. In contrast, nitrogen isotope ratios of A. obscurus did not differ between individuals captured at mineral lick versus control sites. The study from Ecuador concludes that pregnant and lactating fruit-eating bats do not visit mineral licks principally for minerals, but instead to buffer the effects of secondary plant compounds that they ingest in large quantities during periods of high energy demand. However, I don't understand how this study concludes this based only on measuring nitrogen isotopes as these don't show anything about the bats needs for other micro-elements or nutrients – especially since the study also shows that the soils have elevated levels of several elements compared to the bats diets. I think the broad conclusion is dubious – especially since the study only caught 28 bats. In addition the authors ignore that the standard error of the amounts of elements in a fruit or insect diet are very close to the minimum amounts required by small mammals, so this cannot be ruled out as quickly as they have done.
Adriana has this to say about her study: In south-eastern Peruvian Amazon, large numbers of frugivorous bats regularly visit natural forest clearings known locally as collpas. Bats arrive at collpas to drink water that has accumulated in depressions created by larger geophagous mammals that consume exposed soil. Although collpa visitation is common, little is known about its causes and its ecological implications for the bat community. Adriana and her team compared patterns of use of collpas and non-collpa forest sites by bats. More species were captured at collpas than at non-collpa sites, and collpas were visited almost exclusively by frugivores. Overall, bat-capture was higher at collpas than at non-collpa sites, although some species of frugivorous bats were captured more frequently at non-collpa sites than at collpas (e.g., Carollia spp.). Irrespective of capture site, more female bats were pregnant or lactating than not, but there was a distinct female sex bias in bats that visited collpas: 70 percent of bats captured at collpas were female, whereas 44 percent of bats captured away from collpas were female. These patterns suggest that collpas may provide important resources for frugivorous bats in Peru, just as they are thought to provide important resources to the vertebrates that consume collpa soils.
Whoever you choose to believe, this adds to the evidence that collpas are important conservation targets in the region.
