Canoeing across the Agujitas River at night, between Aguila de Osa Inn and Drake Bay Wilderness Resort, Gianfranco and I encounter colonies of Bulldog Fishing Bats most nights.  The Bulldogs use their acute sonar to detect ripples on the water's surface created by small fish.  Once the bat has honed in on the fish, it will rake its hind feet through the water, gaffing its prey.

The fish may then be eaten while in flight or stored in its modified cheeks and eaten later at a feeding perch.  If the bat should accidentally tumble into the water while hunting, they do swim quite well.  Once the bat reaches the shore, it will climb up the nearest tree or vertical surface until it is high enough to become airborne again.  

According to C. Brandon in Costa Rica Natural History Noctilio leporinus bats adapt quite well to captivity:

"Within a day or two of capture it will spontaneously learn to eat from a dish of fish or mealworms placed in the cage. Taming is also rapid, and within a few days the bats can be held in the hand without trying to escape....These bats are also easy to train for experimental work. They quickly learn to do a variety of tasks."

Greater Bulldog Bat feeding on a fish - Noctilio leporinus

John Kricher, in his wonderfully informative book A Neotropical Companion recounts how he once shared a hotel room with a Bulldog Fishing Bat his colleague captured to bring to the U.S. for study. The bat spent the evening dining on a bucket of fish while hanging form a picture frame in the bathroom. "The fact that the bat reeked of fish and strong musk, plus the constant sound of fish bones being ground up", said Kricher, "made for fitfull sleeping that night." Captive bats have lived 11.5 years.

During the day, Bulldog Fishing Bats roost in caves, the crevices of rocks, hollow trees, and sometimes buildings. Colonies may number several hundred bats, although we have never found such large groups in Drake Bay.

References:

Beletsky, L.  2005  Travellers' Wildlife Guides Costa Rica  Interlink Publishing

Janzen, D.  1983  Costa Rican Natural History  University of Chicago Press

Kricher, J.  1989  A Neotropical Companion  Princeton University Press

LaVal, R. & Rodriguez, B.  2002  Murcielagos de Costa Rica/Bats  Editorial INBio

Wainwright, M.  2002  The Natural History of Costa Rican Mammals  Zona Tropical

Wilson, D.  1997  Bats in Question  Smithsonian Institution Press