Scientific American - USA (2022-04)

ADVANCES

16 Scientific American, April 2022

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RESEARCH METHODS

Bat Inspection

Switching equipment can dramatically alter scientific results

Last year biologist Gloriana Chaverri and her students confirmed a hunch about trapping
bats to study and release. They experimentally hung fine-corded monofilament nets in
Costa Rican foliage, snagging 125 bats from 20 species. Meanwhile typical, thicker-
stranded nets captured only 90 of the flying mammals from 14 species. In Royal Society
Open Science, her team from the University of Costa Rica and Smithsonian Tropical
Research Institute explores how equipment choice can influence what scientific expedi-
tions reveal. And Chaverri says that although the finer nets changed the researchers’ group
dynamics—there was less chatting because they had to pay more attention to extract bats
from the tangle-prone web—monofilament nets are now a fixture in her tool kit.
Scientific AmericAn spoke with Chaverri about bat-catching protocols, elusive insecti-
vores and what new takes on old technology can reveal about an ecosystem’s inhabitants.
— Leslie Nemo

How do you hang nets to catch bats
in the wild?
The best places are cluttered but not so
much so that the bats are not flying along
those routes. If the area is devoid of vege-
tation, then the bats will very easily detect
the net. The nets are always hanging close
to the ground, and if you’re not experi-
enced, stretching the nets takes a long
time because you need to be very careful—
they get tangled in your clothes.
The best time to open a net is right at
sunset because the bats are so hungry by
the end of the day that you get the majority
captured between six and eight [P. M .] here
in Costa Rica. Usually we try to stay until
midnight. For the regular nets people have
been using for years, the threads are resis-

tant to the bites from most species of bats,

so we open up the nets and then keep visit-

ing them every 15 to 20 minutes.

What made you want to formally test

the differences between the older,

thicker nets and monofilament ones?

The first time I saw this type of net was

in 2013 at a bat meeting in Costa Rica.

I’m always up for trying new things, so

I purchased one. I went out one time,

I placed the net, and all of a sudden I was

capturing these species that I had never

captured before. I started thinking:

“Hmm—this is interesting.”

I did a project a few years back in Uru-

guay, and we purchased only monofilament

nets. I was presenting the results to other

bat researchers, and they asked me, “How

on Earth were you able to capture so many

bats?” I showed them the nets, and they

were all very excited. That’s another point

that made me think maybe this should be

published, because a lot of people don’t

know about the availability of this other net.

What did you find when you specifi-

cally compared the two nets?

I think the differences were very noticeable.

The main thing is the species that we’re

getting: the regular nets are missing a lot

of the insectivorous bats that we normally

see very rarely. Untangling bats from a

monofilament net really is more challeng-

ing overall. The threads are difficult to see,

so if researchers are not careful they could

unintentionally pull a thread tangled

around soft tissues and hurt the bat.

Another study recently compared dif-

ferent net designs and found that very

fine nets were less successful. Why do

you think that is?

The bats are good at chewing up the

monofilament net and getting released.

[The other research team] checked the

nets as if they were regular nets, every 15

or 20 minutes, [compared with our study’s]

every two to five minutes. Sometimes you

don’t have enough field personnel to be

checking the nets so often. I think the

combination of our two papers shows the

pros and cons of using the monofilament

nets... and will allow a lot of people to

start thinking more about what equipment

to use, based on the questions they have.

People place [traditional nets] and assume

that whatever they’re getting is what’s out

there. Of course, many studies show that’s

not true—but we still use them.

How big a role do equipment choices

like these play in what you learn?

Oof—yeah, they play a big role. [Papers

suggest] we’re missing a big part of the bat

assemblages that we have, for example,

in the Neotropics.... I think the monofila-

ment nets are one of those instruments

that we have to take advantage of, espe-

cially because they’re fairly cheap and easy

to use. I keep telling everyone about these

nets. Whatever way I can help researchers

reach conclusions that are closer, more

or less, to the truth, I think that’s definitely

a good thing for everyone.

Pallas’s long-tongued bats were

more common in fine-corded nets.