Last Monday I lead a bat
monitoring session with some local high school students. Earlier this year I
gave some bat presentations to several classes at the high school and attended
the “Creekies” meeting after school. The Creekies are a small group of students
who are interested in biology and ecology and who want to participate in
after-school work at the creek site behind the school. They are helping with
revegetation of the creek area with native plants and are planning to build and
install some bird (and possibly bat) boxes in the area. They learn all about
the native flora and fauna and get hands-on experience with conservation work.
Anne Craig, the teacher in
charge of the program, asked me to come out to one of their meetings and lead a
bat monitoring session. Of course I said yes (of course after getting the
necessary ethics permit through Terry)! I met them at 5:00 to set up a harp
trap along the creek. I explained the general criteria for choosing a harp trap
location. It’s best to set them up in some sort of corridor that would funnel
bats, such as a vegetation corridor. We then walked around to pick a suitable
spot. The area was dominated by tall gum trees with little undergrowth. Because
of this, most of the bats I expected to see flying around would likely be bats
that forage higher in the canopy (or above the canopy) and therefore have
little chance of being caught. We therefore chose a spot in the (dry) creek bed
next to a large tree and under a large overhanging branch. Bats often use
landscape features such as creek beds and treelines to navigate and commute, so
we had more of a chance of catching a bat here compared to the open areas along
the creek. By the time we set up it was getting dark (around 5:45pm) and we
could see some bats flying high overhead through the canopy. Luckily for us it
was nearly a full moon, which made it bright enough to continue to see the bats
silhouetted against the sky throughout the session. It was also a fairly warm
night compared to the past few weeks. It is now fall here, and the daytime
temperatures have been falling and averaging in the upper 50s/low 60s
(Fahrenheit), with nighttime temperatures in the 40s. While this is definitely
mild weather for me, the bats usually become less active on colder nights when
there are few insects out. That’s why we lucked out with a warm night: a better
chance of catching something!
Deciding where to set up the harp trap.
Helping the students set up their first
harp trap.
The completed trap, set up in a dry
creek bed beside a large tree.
After assembling the harp
trap, we moved away and gathered to look at some bat field guides to see what
species of bats we might catch. Sixteen species have been recorded in this region,
14 of which are microbat species and which we could possibly catch (the other
two are megabats: the Grey-headed and Little Red Flying Foxes). A few of the
more notable ones are:
1.
White-striped Freetail Bat (Tadarida
australis): The echolocation calls of this bat can be heard by the human
ear. They sound like a sharp “tink tink” at one tink per second. Or put another
way, they sound like two 50-cent pieces (or two US quarters) clinking together.
This is a high-flying species and can often be seen foraging for insects around
house or field lights at night.
2.
Lesser Long-eared Bat (Nyctophilus
geoffroyi): A very common bat with large ears. They can catch insects
mid-air (like most of the bats in the region do) or from the ground or
vegetation.
3.
Little Forest Bat (Vespadelus vulturnus), Southern Forest Bat (Vespadelus regulus), and Large Forest Bat (Vespadelus darlingtoni): These three species can easily be
confused, but males can be told apart based on their penis shape. Kudos to
whoever figured that one out!
When going through the bat
species and talking about the White-striped Freetail Bat, one of the kids
chimed in, “Is that the bat that sounds like two 50-cent pieces clinking
together?” He had remembered my comment about that during my bat presentations
to their classes over a month ago! A few minutes later, another boy commented,
“I’ve seen lots of bats flying around the footy field lights at night hunting
for insects.” I was so pleased that they had remembered all that and had taken
what they learned in the classroom into the “real world”. It felt good to see
them using the knowledge they learned during my presentations.
Looking through the bat field guides to
see what species of bat are in the area.
The next activity was walking
around with the Anabats to listen for bats flying around. Anabats are acoustic
detectors that pick up the echolocation calls of bats and convert them to a
lower frequency that we can hear. We can also hear when bats are feeding by the
“feeding buzzes” they use, which are a quick succession of echolocation pulses
that sound like a buzz and allow the bats to hone in on an insect. Anabats, and
other acoustic detectors, are used in research studies to monitor overall bat
activity and foraging activity in an area. In addition, species can be
identified by their calls (some species more easily than others). I wanted the
students to see how Anabats work and to see them in action, so we took a walk
around the creek listening for bats. Since it was a relatively warm night,
there was plenty of activity and all the detectors lit up with clicks as bats
flew overhead. Because of the moon, we could even see the bats flying as we
heard them on the Anabats. We also heard a few feeding buzzes so we knew the
bats were having some success at finding insects.
At 6:30pm we headed back over
to check the harp trap. Normally with harp traps you set them up in the evening
(before the bats come out) and you leave them up overnight and check them in
the morning (before the sun comes up). I had never used harp traps before
coming to Australia;
I’ve only ever used mist nets. Harp traps are great because once the bats fall
into the cloth bag, they calm down and usually end up sleeping until the
researcher checks the trap. It’s a very low-stress situation compared to mist
nets, in which the bats get tangled and quite stressed (which is why mist nets
must be checked EVERY 10-15 minutes the entire time they’re up). If we had been
doing a real survey of the bats in the area, we would have left the trap up
overnight. However, I just wanted the students to see the process of setting up
and taking down a harp trap, as well as possibly see some bats up close.
Amazingly we did catch one bat! I hadn’t expected to catch any due to the
recent cold weather and the less than ideal area for harp trapping. It was
definitely icing on the cake. It was a female forest bat, probably a Little
Forest Bat (Vespadelus vulturnus). It
looked like she had just been caught, as she was still at the bottom of the bag
and hadn’t crawled up the sides yet. She was either commuting through the creek
bed or possibly hunting there. Lucky for us! We went through the standard
recording procedure for bat surveys, which included recording the species, sex,
age (unless a bat has been previously banded, it’s impossible to tell its
“exact” age, so we determine whether it’s a juvenile, sub-adult, or adult based
on the amount of fusion of the wing joints, with adults having completely fused
joints), forearm length, weight, and anything else notable. One student used
calipers to measure the forearm length (while I held the bat, of course) and
another recorded. I also got to show them a bat fly crawling around in the
bat’s fur. Bat flies are ectoparasites that have co-evolved with bats to only feed
on bat blood. They are often species-specific, meaning that certain species of
bat flies only live on certain species of bats. The students thought it was
pretty cool.
Once we had recorded all the
data, it was time to let the bat go (she’d definitely had enough excitement for
one day!) and take down the harp trap. I’m still not a pro at setting up/taking
down harp traps, so it took a few minutes, but with help from the students we
got it done. As we walked back to our cars, they were all chattering excitedly
that we should do this again. Since winter is coming and the bats go into
torpor for most of it, we probably won’t do a session this term, but if I’m
still around next term we might try another one then. I hope we do because I
had a ton of fun and the students did too. I think there’s no better way to get
people (of all ages) interested in and involved with science and nature than
through direct, hands-on experience. And after seeing a bat
up-close-and-personal, who would NOT love these amazing little creatures?
Having a look at the bat we caught.
Little Forest
Bat
Checking the wing joint to determine the
bat’s age.
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