Tonight is the night – I waited a long time but tonight we will finally go out and collect some bats! Phyllostomid bats, to be precise, New World leaf-nosed bats. We are particularly interested in the fringe-lipped bat (Trachops cirrhosus), which Rachel Page, who was so good to add me to her collecting permit (thank you, Rachel!), needs for experiments in her BatLab. Not sure how the evening is going to look like but I know this: I AM IN FOR A TREAT!
The nose leaf of these bats is a unique feature for the Phyllostomidae, now what is its function? At first sight it looks pretty useless, such a big piece of cartilage on the nose. And heavy, right? However, it has a function in echolocation (sending out and interpreting incoming high frequency sounds). There is no sexual selection happening — both males and females have a nose leaf. But one recent study found dimorphism between sexes (of Mimon crenulatum bats); the nose leaf of females is larger than the one of males. This has a positive effect on the echolocation and thus on the ability of finding food. This didn’t come just random — of course not: it is a strategy for parental care, which females are providing for the offspring.
After preparations in the heat of the sun, Rachel and her team decide how to run the evening: they will split up in two teams – I join the group focusing on Trachops cirrhosus, the fringe-lipped bat, which shows wart-like papillae on its lips, hence the name, and feeds with frogs. We set up six mist nets in semi-open spots in the jungle of Gamboa; these are wide nets of fine mesh suspended between two poles with loose, baggy pockets to capture birds or bats that then get tangled. We also brought two MP3 players, not for loungy background music, but to attract the bats. Our friend the fringe-lipped bat likes some frog every now and then (especially the túngara frog, Engystomops pustulosus) and uses the calls these frogs make to find its food. We have these calls on our MP3 player. Hence bats will come look for food, but will find some nets instead. Pure deception, I say!
At dusk, we start patrolling the nets for the first time and we already have our first capture: a striped hairy-nosed bat (or Mimon crenulatum in Latin). Its nose leaf is very elongated, you could call that thing a spear-nosed bat. The poor creature is completely entangled in the net, but luckily these people know exactly what to do — they free the bat leg by leg, wing by wing, sometimes tooth by tooth, while holding it with one hand not to be bitten (thumb at the head, index finger at the chest). My presence tonight marks a bit of a change from the usual business: we screen the bats for ectoparasitic bat flies, because these flies on their turn can carry ectoparasitic fungi (Laboulbeniales), which I study for my PhD.
As the evening passes by, we capture several species of bats: jamaican fruit bat (Artibeus jamaicensis, nicknamed “AJ”), Pallas’s long-tongued bat (Glossophaga soricina), the common Seba’s short-tailed bat (Carollia perspicillata), and fringe-lipped bat (Trachops cirrhosus). The three first species are freed after handling, disentangling, and screening for bat flies. All captured fringe-lipped bats are stored in (colorful!) washcloths made of fleece. At some point, all six nets have one or more bats entangled, and since we only have four hands (I am not dealing with the bats themselves, just observing [rabies, you know]) we decide it is time to start taking down a few mist nets. The MP3 player is shut down and we slowly get to the point that all of our by-catch is released, the nets have been broken down, and we have some ten fringe-lipped bats hanging in their washcloths. Time for detailed inspection, it is Rachel herself who does this final check. For females, is she pregnant? is she nursing? If yes on either of these questions, the bat is released. For males she selects the most alpha-male and releases the others. We are left with one useful bat and decide it is time to go home. When we get back to the BatLab, my taxi is already waiting to get me back to Sarah. What a great evening!