Cruising along the canals of the Corcovado/Sierpre waterways and the driver pulls up to a tree. The wind is blowing and it is noisy. I am not sure what he is saying. Then, I see what he is talking about. Tiny little bats located on the underside of the tree trunk. They are motionless and I was able to get a pretty good photo.

Bats are the most numerous mammal in Costa Rica and there are 109 species. Most bats avoid the bright light of daylight and are seen slumbering halfway up a tree. Bats are the only flying mammal and they fly at night to seek out insects. Most people fear them but they are important to the ecology as they pollinate flowers, clear the air of pesky gnats and mosquitoes, rid the fields of mice and drop seeds which restores the forest. Some bats use sonar or echolocation to determine what is around them.

There are three species of vampire bats, called vampiros by Ticos, in Costa Rica and these can be problematic as they cause damage through the transmission of rabies and other diseases. Two species of vampire bats feed on birds, while the third feeds on mammals. It's estimated that vampire bats cause $100 million in damage on domestic farm animals throughout Central America.

Bats measure around 30mm (1.14 in) in size and weigh about 2g (0.07 oz). They are terrestrial and light boned. Bats have thinner wings than birds and maneuver more quickly and more precisely than birds. The surface of a bat's wing has small bumps that are touch-sensitive receptors. Each of these receptors cells has a tiny hair in the center of it and is sensitive to the stretching of the membrane.

The eyes of most microbats are small and poorly developed but they are not blind. Vision is used to aid in navigation, especially in long distances and beyond the range of echolocation.

Behavior of bats

The social structure of bats vary. Some lead a solitary life while others live in colonies. A phenomenon known as fission fusion is part of some bats social structure. The fusion refers to a large grouping of bats roosting in a specific area. Fission is the breaking up and mixing up of subgroups. Individual bats will switch roosts with other bats and find new trees and new roostmates.

Bats have a communication system where they make a range of sounds and other bats will respond.

Food for bats

Bats eat fruit, insects and three special survive on blood. The bulldog bat feeds on fish.

Most bats have a breeding season which is usually in the spring. Bats can have between one to three litters per season. Females have one offspring per time and nurses it until it is nearly adult size.

Female bats control the timing of pregnancy so that the delivery coincides with maximum food intake and favorable ecological factors. Mating can occur in the fall, but the female can delay fertilization until the spring.

The wings are too small to fly at birth so the young are dependent on their mothers until 6-8 weeks of age. Megabats are dependent until 4 months.

In Tortuguero National Park, the bulldog bat fishes. Its wingspan reaches 60cm across and its claws are large enough to hook a fish.