General Bat Biology

One of the best parts of Piro Biological Station is that it is a true research station with multiple people from across the world coming to do their research in the Osa. A few weeks ago, bat researcher Melquisedec Gamba-Rios, a PhD student at the University of Tennessee-Knoxville, gave an introductory talk on the biology of bats. Melqui is at Piro for three months gathering data for his dissertation and I learned a lot from his talk.

Of the over 5200 species of mammals on this planet, bats make up 1200 of those species (21% of all mammals). They are the second largest group of mammals after rodents. Costa Rica alone is home to 117 species of bats.

Bats aren't blind, but they can't see very well at night. During the day, though, they see just fine. At night, they rely on echolocation, which you've probably heard of. Bats produce ultrasounds as they move and they need to keep moving so that they can send these sounds in different directions. They use their ears, of course, but bats also use their nose lip to "see" differences in textures.  They can move this nose lip to give direction to the sound they're sending out. They change the frequency of the sound they're sending out depending on their location. For example, bats will send out a flatter signal in an open area than in a forested one.

Bats roost in caves typically in the United States but they can also use holes in trees. Some bats in the tropics specialize in roosting in fallen trees over creeks or rivers. They have a social system with the alpha male roosting on top. Very uncommon are bats that roost on leaves in the tropics. There are bats that will make a tent-like structure out of large leaves by biting through the leaf to make a roost. Of the 112 bat species in Costa Rica, 17 modify leaves in some way.

Styloctenium wallacei roosting in tree

I was particularly interested in learning what Melqui had to say about the diet and feeding ecology of bats. Most bats are insectivores, consuming insects, but some species consume fruit, nectar, or even fish or small birds. One bat can consume 700-1000 mosquitos per hour. Fruit-eating bats are important seed dispersers, as bats will consume the juice of the fruit but spit out seeds, meaning these seeds remain intact and can grow away from their original tree. There are three species of bats that fish and two of those species live in Costa Rica (Noctilio leporinus and Noctilio albiventris) . They echolocate off of the water and can consume five to six tiny fish per night. These bats have adaptations to help them fish such as large feet and claws to snatch their prey out of the water. The echolocation these bats send when over the water is so loud that the bats will actually close their ears when they are directly over the sounds.

Of course, Melqui had to devote part of his talk to vampire bats, or bats that use their incisors (not their canines) to feed off of the blood of other animals. There are three species of vampire bats and they are all found in Costa Rica. An anticoagulant is in their saliva so that they can consume more of another animal's blood without it clotting. Vampire bats drink two teaspoons of blood per night and, if they don't eat for two or three nights, they die. To prevent death, bats can detect when another bat needs blood and can give it to them. However, this type of help only happens between family groups. Vampire bats will actually land close to their prey and then walk up to the animal so as not to startle it. Their nose is specifically shaped to detect hot areas of skin where blood is. And, while yes, bats can carry rabies, there are more problems in the United States with raccoons and rabies than with bats.

To learn more about bats, I recommend the following website: Bat Conservation International.

Food for thought: Why would vampire bats only help members of their own family? (Think about evolution and an individual's fitness, or ability to survive and produce viable offspring, thus contributing to the gene pool of future generations.)