White-lined bats are some of the most conspicuous bats you are likely to see while visiting the Osa Peninsula. These clever little bats are fond of using the overhangs of houses, or ecolodges, as their roosts and have learned to coexists with humans even in very altered environments.

There are two species of White-lined Bats in Costa Rica and they are both very similar: the Greater White-Lined Bat (Saccopteryx bilineata) and the Lesser White-lined Bat (Saccopteryx leptura). The Brazilian-long Nosed Bat is the only other Costa Rican bat with two white lines on its back, but it is easily distinguished by its flecked, grayish fur and very long nose.

White-lined Bats are quite small, with adults normally measuring about 5 centimeters. They are also called Sac-winged Bats because they have a sac shaped scent gland on their wings, near the forearm.

Lesser White-lined Bat - Saccopteryx leptura 

Lesser White-lined Bats live in small colonies. Males and females tend to form long lasting, monogamous pairs. Male bats fill their sacs with saliva, urine and other secretions. These liquids ferment and provide the males with a perfume which is unique to each male. Scientists believe this scent helps female bats choose their mate.

Greater White-lined Bats normally live in small harems made up of one male and up to eight females, but colonies of up to fifty bats have been documented. These large colonies are usually made up of several coexisting harems. Females will frequently switch to other harems while males normally remain tied to their territories.

White-lined Bats are strict insectivores. They begin foraging while it is still light out and hunt through the night. While foraging they fly at an average speed of 5.75 meters per second and eat mostly small beetles and flies. Males normally defend a foraging territory and each female in the harem has her own foraging territory within that space.

During their breeding season, harem males serenade each female as they return from foraging. They will indulge in long, complicated songs which are audible to humans. As they sing, they will periodically hover in front of the females and perfume them with their scent.

The perfume, which is also easily detected by humans, is released from the scent sacs on their wings. This ritual may take place several times throughout the day. Rival males will also partake in long "scent flights" with one another, specially when their territory shares a common border.

Despite all of the singing, displaying, and perfuming, copulation for the Greater White-lined Bat only takes place during a short period late in the rainy season. Females give birth to their pups in May, in sync with the return of the rains. This pattern is different in the Lesser White-lined Bat, and females may produce two litters. In this case they will give birth in May and in October or November.

Female Greater White-lined Bat with her pup - Saccopteryx bilineata

The newborn bats suckle for several months, although they can usually fly on their own when they are two weeks old. Females provide all the parental care to the young bats. Each night, when females go out and forage, they take their pups away from the daytime roost to a secret hiding place for them to pass the night safely. Each pup has its own hiding spot. In the morning they retrieve the pups and return with them to their daytime roost.

In August and September, when they are three to four months old, the new generation of White-lined Bats will leave the harem. Studies have shown that females consistently leave the area, while about half of the males will attempt to establish their own harems nearby.

References:

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

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