Taking Care of Business While Hanging Upsidedown

Have you ever wondered how a bat can poop and pee, while upside down, and not end up a filthy mess? I must admit the thought had never occurred to me. I guess I just assumed that sometime during their evolution that issue would have sorted itself out.

It is thought that bats began roosting upside down early in their evolution because dropping head first from their roosts makes it easier for them to take flight. By hanging from their feet bats are able to spread their wings before letting go of their roost and are poised for flight as soon as they hit the air.

Notable exceptions to this rule are Disk-winged Bats, which roost right side up. These tiny insectivores roost in groups inside rolled Heliconia and Banana leaves. Suction cups on their thumbs and heels enable them to stick to the sides of the leaves.

Thyroptera tricolor Disk-winged Bat

Disk-winged Bat, Thyroptera tricolor, roosting in a Heliconia Leaf. Click on the image for a larger picture

But I diverge…back to the pooping and peeing. About a week ago we came across a Tent-making Bat, Artibeus watsoni, and as we watched the little bat began to pee….and it was amazing! It didn’t get a single drop on itself!

A few days later, while on the tour, I spotted a bat feeding in a tree about 7 meters off the ground. I knew right away it was not one of the typical fruit bats we tend to see. It was quite small and had very light colored fur. I got it on the scope and we watched it as it fed.

Then suddenly, without releasing its fruit, the little bat arched backward and took a big poop followed by a lengthy pee! Once again its form was impeccable and it managed to keep itself and its fruit feces free. After it finished, it went right back to what appeared to be a very enjoyable meal. Fortunately, while we were watching the bat I shot some video. I have posted an excerpt of the video, which Tracie set to a catchy tune, below…

It turns out that this cute little bat, Chiroderma villosum, is not a common one to see at all. During all the years of doing the Night Tour we have only seen it a couple of times. Their common name, the Hairy Big-eyed Bat, is quite fitting. They have really big eyes for a bat and long shaggy fur. They are quite distinctive from other fruit bats as they have light colored fur and very faint, barely visible facial and middorsal stripes.

Hairy Big-eyed Bat, Chiroptera villosum

Hairy Big-eyed Bat, Chiroptera villosum. Click on the image for a larger picture

Next to nothing is known about these little bats. Their roosting sites are unknown and they are only known to feed on 3 species of fruit. They are rarely captured in mist nets and it is thought that they dwell mainly in the canopy. We feel fortunate to have observed this little guy and to have gotten a glimpse into its otherwise secretive life; including its feeding and toilet habits.


LaVal, R. & Rodríguez, B. 2002 Murciélagos de Costa Rica / Bats Editorial INBio

A celebration of wrinkles!! The esthetics of the Wrinkle-faced Bat

It is safe to say that Tracie and I love bats. Fortunately for us Costa Rica has massive diversity when it comes to these flying mammals. Scientists have identified around 240 mammals in Costa Rica of which 113 are bats. The Osa Peninsula has the highest bat diversity in the country with 80 identified species.

Even so, bats can be elusive during the Night Tour. Most of our sightings are fleeting views of bats flying by at breakneck speed. At times we are also approached by insectivorous bats capitalizing on the insects attracted by our headlamps.

Occasionally we are fortunate enough to encounter roosting bats which we can observe in detail. These prized encounters, although usually brief, are always memorable. By far the most memorable bat encounter we have had is with the Wrinkle-faced Bat, Centurio senex. Wrinkle-faced Bat - Centurio senex

This bat is so different from other bats it is the only member of its genus: Centurio. The binomial name is derived from the Latin words centurio, meaning 100, and senex, meaning old or aged, because its face looks like that of a 100 year old person.

It is not known why these bats evolved such a wrinkly face, but it is though that perhaps the wrinkles act as canals to channel juices into the bat’s mouth as it feeds on ripe fruit.

Male bat’s faces are wrinklier than the females’ faces and they also have chin folds which they stretch over their faces while roosting. A swollen ridge along the bat’s foreheads prevents the face mask from slipping and, incredibly, the masks are complete with transparent “window panes” over the area covering the eyes!!

Wrinkle-faced Bats have a very short and wide skull which allows them to apply about 20% more force in their bite compared to other similarly sized bats. Scientists believe that this allows Wrinkle-faced Bats to feed on harder fruits than other frugivorous bats. They also have pouches in their mouth where they can store spare fruit.

Wrinkle-faced Bat - Centurio senex

Wrinkle-faced Bat feeding on fruit. Notice its massive thumbs!!! Click on the photo for a larger image

Another impressive feature about these bats are their massive thumbs. It seems this is an obvious adaptation which allows the bat to grip and feed on large fruit, although their feeding habits are poorly understood. Very little is actually known about these handsome bats. Roosts are rarely found and scientists think they may roost high in the canopy.

The facial features of the Wrinkle-faced Bat make it one of the most unusual mammals in Costa Rica. Some may say they have a face only a mother could love. To us, though, their unique looks represent the beauty and diversity awaiting discovery in the tropical rainforest.
Wrinkle-faced Bat - Centurio senex

LaVal, R. & Rodríguez, B. 2002 Murciélagos de Costa Rica / Bats Editorial INBio
Wainwright, M. 2002 The Natural History of Costa Rican Mammals Zona Tropical