Here are some bats sleeping on the underside of a tree along the river bank. This photo was taken from a boat on a wildlife viewing trip such as yesterday's raft trip. The bats were sleeping during the day on the shady part of a tree. At night they will fly off the tree on which they roost to eat insects. At night they will use a different tree to roost while feeding.
Bats are the second most common type of mammals. Only rodents have more species than bats. 105 of the world's 980 species of bats live in Costa Rica. I have seen bats only in small groups such as this on a wildlife viewing river trip, but have not seen bats flying around at night in Costa Rica.
Bats such as these tend to hang upside down because it makes it easier for them to take off and fly by dropping from their roost rather than having to take off and overcome gravity. They tend to feed mostly in the hours after dusk and before dawn, being less active in the middle of the night, and being inactive during the day.
I cannot identify the specific type of bats shown in this photo, as I was content to view them from a distance from a river boat, rather than getting up close. I prefer to let sleeping bats hang.