La Selva and its bats – they will never let you go!

Martina Nagy, University of Erlangen, Germany, REU Mentor

Muddy, sweaty and happy me with our night's bat catch (Picture: M. Lopez).
Muddy, sweaty and happy me with our night’s bat catch (Picture: M. Lopez).

Wow, I guess it has been more than ten years now since I started working in my most favorite and beloved forest of La Selva. I got there first in 2004 to do field work for my masters thesis on the greater sac-winged bat (Saccopteryx bilineata). And ever since, I keep needing to come back because it is just so wonderful to get soaked every day out in the field, get covered in bug bites, and smell so unimaginably bad that even the peccaries seem to wonder, then have a shower accompanied by frogs, cockroaches, spiders and/or bats, depending on the cabina you are at, followed by checking my pillow and sheets for gecko poop (which is definitely still better than bat poop) and falling asleep to the sound of thundering rain in a cabina that does shake with the thunder and lightning and sometimes even with an earthquake, the latter of which is quite unusual and scary for a person from Central Europe!

Well, all joking aside, it simply feels like a great privilege to work in a tropical rain forest where other people like to spend their vacation. I have also had the great fortune to join the long-term project on the greater sac-winged bat, which is one of the best studied bat species worldwide with respect to its social system. Bats are highly social animals, and, in spite of their small size, very long-lived, but (and this makes their social lives a hassle to study) nocturnal and generally living in secluded, not easily accessible day roosts.

Emballonurid bats love such luxurious buildings.
Emballonurid bats love such luxurious buildings.

Fortunately, the latter is not true for members of the bat family Emballonuridae, of which S. bilineata is a member. Emballonurids preferably live in rather light day roosts (like on the buttresses or trunks of large trees or even on the outside of inhabited buildings) where the group members mostly roost without body contact and are easily habituated to the presence of curious bat scientists. That means that I can simply sit in an abandoned building that has been claimed by a group of greater sac-winged bats and observe their social interactions.

S. bilineata pup after banding.
S. bilineata pup after banding.

Male S. bilineata defend a territory (1-2 m2 of vertical surface) in the day roost in which up to seven females roost, which we call a harem. To make sure that territorial properties are respected by other males they will mark their territorial boundaries with secretions from their gular glands and utter territorial songs every morning and evening. Males have also an intriguing courtship repertoire, consisting of olfactory, visual and vocal signals. Every morning year-round, males will fill their wing sacs with numerous body secretions and will try to wow their harem females with elaborate hovering displays during which they fan the odiferous contents of their wing sacs towards the females. Being a Saccopteryx male is a tough job! The more so as female sac-winged bats are bigger and more aggressive than males (girl power yeah!) and might just decide to mate with another male instead of their own harem male. In large colonies with many adjacent harems only about 30% of pups born in a harem are actually fathered by the respective harem male. What a poor reward for a year’s constant courtship efforts!

Small S. bilineata harem. The harem male is on the left and the other two bats are his harem females. Our bats have coloured bands on their forearms to allow individual identification (Picture: L. Günther)
Small S. bilineata harem. The harem male is on the left and the other two bats are his harem females. Our bats have coloured bands on their forearms to allow individual identification (Picture: L. Günther)

As you might have guessed I am a behavioral ecologist, interested in animal behavior and especially in how certain behaviors evolve. What started with a small project in my master thesis concerning reproductive success of male sac-winged bats in small versus larger colonies has turned into a much bigger long-term project on vocal and social complexity and evolution of exceptional female-biased dispersal in emballonurid bats. From the very beginning I have been working in a team along with Mirjam Knörnschild, Frieder Mayer, Otto von Helversen, Christian Voigt, Barbara Caspers, Linus Günther, Maria Eckenweber and many more as well as lately with my two REU students Marlena Lopez and Kyle Reid. No long-term project is possible without good team work, and this is probably one of the most important lessons I have learned in the past years.

From Prof. Otto von Helversen I have learned that asking the right questions in science is much more difficult than finding the right answers. Together with my collaborators we have so many (hopefully good) questions by now, that I am looking forward to another decade (or maybe more) of working on the evolution of the social systems of this great and astonishing family of bats in La Selva. Not least because coming to La Selva also means that I will get to spend time with many dear friends that like me are infected with the tropical rainforest virus and keep coming back!

So my dear REU students: Kyle and Marlena, I have enjoyed getting to know you, working with you and being able to share some of my passion for emballonurid bats and the tropical rain forest with you. Seeing you guys being so excited about catching, handling and observing bats reminded me of what a wonderful job I have – thanks a lot for that!

Biking in the rain forest is the coolest thing! (Picture: L. Günther)
Biking in the rain forest is the coolest thing! (Picture: L. Günther)