by Jane McMillan-Brown
Why would we spend a couple of days placing, baiting, and setting 80 traps along
six-tenths of a kilometer of trail? What will we do with whatever is trapped?
How do we know that only the animals we want will enter the traps? Will they
get hurt when the trap springs shut? Will they ever be free again? When? How?
Where?
These were some of the questions I had when I learned that this year we would
be trapping squirrels. Maybe you have some of the same questions as you come
along with me and learn some of the hows and whys of mammal trapping. If you
have different questions, maybe you'll find time to send them to me along with
your thoughts and I'll share everyone's responses.
Now for some of those earlier questions: First of all, it is squirrels we want
to catch for the purpose of marking them for future observation and study. Giving
them each their own identification makes it possible to keep track of when they
are seen again, where they are seen, (for example, have they moved to another
part of the island or are they feeding around the same area?), how healthy they
appear to be, and so on. Jackie and Greg have been doing this every other year
and observing the squirrels every January, gathering and recording the data.
Trapping and marking animals is a complex job that requires great commitments
of time, patience, and diligence. Once the traps are actually set, they must
be checked frequently to safeguard the well-being of the animals. But, here
I am getting ahead of myself.
One of the first things we have to do in preparation is to check the traps to
be sure they are in good working order. No sense baiting a trap if the door
won't shut because the metal parts are rusted. Many of the traps have been left
outside wired to tree branches for several years. They are wired open so that
no animals will get caught after we end the trapping season. This helps get
the animals used to seeing them and smelling them in the forest so that they
are not afraid of them. When we go out to check the traps, we know we will be
leaving the trails and walking through brush and vine tangles, so we remember
to tuck our pants tightly into our socks and tie our boots securely to help
protect our legs from the ticks and chiggers. The snakes usually feel the vibrations
we make from walking on the ground or see us coming and they get out of our
way. They really aren't very interested in us if we aren't a threat to them.
We also have a map that Jackie drew which shows where the traps were the last
time they were used. (Have you ever drawn a map, and then given it to someone
to find something?) That helps us locate the traps after we've been away from
BCI for a long time. Traps sometimes get covered with vines or fallen leaves,
and coatis can rip them off the trees and drop them on the ground. Or some traps
get crushed by falling trees and need to be repaired or removed from the forest
and put in the trash. We can mark on the map any new traps we put out or any
that we move to different locations. Once the traps are set so that they will
catch animals, it's also very important to have that diagram showing where the
baited traps are so that we can be sure to check every one for animals and not
miss any. (However, Jackie and Greg usually have all trap locations memorized
by the second day!)
While there are no guarantees that other small animals, besides squirrels, won't
get into the traps, one way to attract the squirrels is to put some of their
favorite fruit in the trap, especially if it's a fruit that they can't get right
now, like royal palm fruit. Jackie had some stored in the freezer for just such
an occasion so that's what we used. The traps are about 50 cm in length by 20
cm wide by 20 cm high. They are made of steel wire and have a trap door at one
end that will spring shut after the squirrel is well past the door. The door
won't hurt the animal when it is closing. We place the bait at the far end of
the trap so that the squirrel enters the trap to get the fruit, which smells
very good to a hungry squirrel.
The trap is set so that once the squirrel walks across a small pan of metal
on the bottom of the trap, the squirrel's weight causes the pan to tip, which
releases a spring that closes the trap door. Some squirrels get more upset than
others and will try to escape. That is why it is important to check the traps
frequently once they are set. We don't want squirrels upset and trying to get
through the small openings in the wire cage. They could bump their noses and
get hurt if they were left too long. We also worry that a predator like a coati
might harrass a trapped squirrel and harm it. One of us must walk through the
forest several times in the morning and again in the late afternoon when the
squirrels are most active and likely to get into the traps. (They often nap
in the afternoon heat of the day.)
Okay, by 11 AM on our second day of preparation, we've methodically checked,
baited, and set every one of those 80 traps and marked our map indicating each
location. After a refreshing drink of water from our portable water bottles,
it's time to start back down the trail, wash up, and get to the dining hall
for lunch by noon. We figure that we'll come back for the first check right
after lunch. But wait a minute! What's that movement over by the trap near the
big Dipteryx tree? Looks like something brown moving in the trap! 'Let's go
over for a closer look.' 'Wow, a squirrel has already found the fruit.' Our
lunch break will have to wait. Squirrel business has to come first now.
We hadn't expected to get one so quickly and we've been caught off guard. Usually,
we'd be carrying an old shirt or towel to place over the trap after we remove
the trap from the tree branch. (It's fastened on with thin wire.) The covering
helps keep the squirrel calm as we carry it in the trap back to the lab for
marking. Well, we all laugh about who will have to sacrifice their shirt for
the cause. This time, Greg drew the short straw and agreed to take off his T-shirt
and cover the trap for the remainder of our walk to the lab Jackie has set up
in one of the buildings near the trailhead. I made a mental note to carry an
extra, old shirt with me next time so I wouldn't have to...you know.
Once inside the lab, the squirrel is left in the covered trap on a work table
while Jackie and Greg get the marking materials ready. This squirrel sits quietly
and feeds on the bait while we prepare. I stand ready with my camera to photograph
the marking procedure. The entire trap, containing the squirrel, is placed into
a large plastic bag and a small cotton ball wetted with an anesthetic is added.
Very quickly, the squirrel goes to sleep. This is the only safe way to handle
the squirrel and keep from being bitten or scratched, while at the same time
preventing the squirrel from being extremely upset. The sleeping squirrel is
removed from the trap and placed in a mesh bag, like the ones often used in
laundries. The bag is then gently laid on a scale. The squirrel's weight and
length are recorded, along with its gender, and any significant markings. Now
it is time to give the squirrel its own special identification marking. So guess
what we use to mark them? Special jewelry! Yeah, really.
Designer jewelry. Nothing but the best for our BCI squirrels! Colored ceramic
beads threaded onto a stainless steel neck chain, custom measured, is carefully
fastened around the squirrel's neck and a numbered tag is attached to its ear.
Each squirrel gets a different color combination and its own tag number. The
ceramic beads won't crack and rot like plastic ones would and the stainless
steel chain won't rust and cause problems for the squirrel. Careful notation
is made of the tag number and color combination of the beads. From now on, for
the rest of its life, this squirrel will be identifiable.
Almost before the tagging is complete, the squirrel begins to stir. We don't
use ether, but instead an anesthetic that both acts quickly and wears off quickly,
with few side-effects. This first one today is a young male who hadn't been
previously caught. Before he is fully awake, he is placed back into the trap
for his return trip to the forest. He will be taken back to the same location,
the trap will again be attached to the branch, the trap door will be opened
and the squirrel will leave it when he's ready. We reset that trap and check
all of the others. Believe it or not, sometimes the same squirrels go back into
the same trap another day. We only mark them once. After that, we just record
their activity and location.
Several squirrels got caught before lunch, so Jackie and Greg have to finish
marking and releasing the squirrels before they can take the time to eat. We
always return squirels to the exact places where they get caught, especially
young ones that could get lost. I agree to go quickly to the dining hall to
see if I can save us some lunch before the food is all put away or eaten by
hungry researchers just back from their own morning adventures.
Now, you might ask, don't other species of mammals besides squirrels like royal
palm fruit? And don't they get caught in these traps? Yes! But this is limited
somewhat by using squirrel-sized traps, so big coatis and big monkeys can't
fit into them. Occasionally a very pesky and determined coati will squeeze into
a trap-- then we have what looks like a cubical coati, all jammed in with its
long nose mashed up against the end of the trap, fur sticking out in all directions,
and no way to turn around. That's another reason why we check the traps frequently--trapped
coatis want to get out NOW! We have caught a whole variety of mammals over the
years: baby coatis and white-faced monkeys, and even a baby anteater (they don't
eat fruit, but can just walk into a trap by accident). We have also caught 'common'
possums, 'four-eyed' possums, pygmy possums, spiny rats, climbing rats, and
a porcupine. Sometimes we catch doves. We let them go, take a picture sometimes,
and record that they were caught, and where.
This year, after 8 days of trapping, we caught more squirrels than we have in
any year since 1979. We certainly don't ever catch ALL of the squirrels: some
are too cautious to enter a trap. We left BCI this year with 23 marked squirrels
living in an area of about 10 hectares. We saw many of those same animals in
our census walks and are using those data to estimate how many squirrels live
in the trapping area, and on all of BCI. We've also learned about the lifespans
of squirrels, that a female might live eight to ten years and raise many broods
of babies, but males often live only three or four years and rarely make it
to eight years. Mapping the locations where we have seen or caught a marked
squirrel also helps us understand how big a piece of forest they need for their
daily activities of feeding and raising a family. Next week we will give you
a quick summary of our mammal census results, and sign off for this season!
Bye!