So now little bit about bat reproduction.
The bats around here typically mate in the
fall and then give birth the following late
spring.
And many species of bats around here have
something called embryonic diapause, and this
is a very cool adaptation that I wish humans
still retained.
And what it means is, when the sperm and the
egg come together, they are going to form
a new zygote, that is a ball of cells, it
is going to start to divide, and divide, and
divide.
And it will float down and then eventually
implanted in the uterus.
Diapause is when that ball of cells stops
and doesn’t implant in the uterus, so the
pregnancy essentially goes on hold.
When it starts to warm up in the spring, and
it seems like there'll be lots of insects
in about six weeks for mom and baby, she’ll
start the pregnancy up again.
And so, she's not making a conscious decision
for this pregnancy to start up, but environmental
cues - day length, food availability, that
sort of thing - are going to trigger the pregnancy
to start again, so that she can have her baby
in an optimal time.
And this allows for seasonal variation - if
you have a late winter, you’re going to
have your babies later, and if it's an early
spring you can have your babies earlier.
Gestation is 45 to 60 days.
When the babies are born, they are pink, relatively
hairless, their eyes are closed.
The moms carry them around for a couple days.
After they’re three days old, they leave
them behind.
And if they're in a roost, with many other
bats, they’ll stash them in groups.
Some famous research was done down in Texas
by Gary McCracken that found that mothers
do locate their pups by smell and sound every
night.
So if you have a cave with 5 million bats,
that means that there will be 5 million babies,
and each one of those, their mother is going
to come back and find them every night.
Now, they'll stash them in groups of 1,000
or 2,000, and one or two females (who clearly
pulled the short straw) will stay behind and
watch that group for the evening.
At 3 to 4 weeks, the pups are going to be
able to fly.
They’re going to start following mom and
start learning where the good spots are to
eat and where the good night roosts are.
This is a baby little brown bat that was several
days old.
It actually fell out of that horse barn roost
that I showed earlier.
This is the smallest possible syringe and
this little bat is sitting on a heating pad.
I mentioned my mom at one point; she wasn't
so sure about me doing bat research, but I
talked her into coming out with me one night,
and that night, about six babies fell out
of the roost, and I put them in a small container,
and I was going to take them to woman who
does bat rehab.
But, in the middle of the night, I heard this
frantic scratching and we shined the light
onto the container, and there were several
adults trying to get into the box.
And so the mothers were trying to come pick
up their babies.
Now the babies are 1/3rd of mom’s weight
when they're born, and a small bat just isn't
going to be able to take off from the ground
holding onto a baby.
So we took the container that we had the babies
in, and we put it on top of a ladder - so
was about 6 feet above the ground - and the
mothers were able to fly in, pick up their
babies, and get enough lift from 6 feet up
to carry them back.
And so, of the six babies that were in the
box at the beginning of the evening, at the
end only, one was not picked up; and that
was this little guy.
I’m not sure what happened, but we brought
them home, we gave him puppy formula overnight.
My mom was completely hooked on bats after
taking care of this little guy!
We got him to the bat rehab person over in
Marin County.
She raised him to an adult, and that fall,
released him back in the same barn.
As far as we know, he's still doing just fine.
So, one of the biggest myths about bats is
that they're all coming after you to suck
your blood.
So of the thousand different species of bats,
only three are true vampire bats, and I always
find it ironic that none of those bats occur
in Europe at all, which is where all the vampire
stories come from.
The vampire bats that we do have, occur in
southern Mexico, Central America, and a little
bit in the northern part of South America.
We don't have any vampire bats here in California.
Vampire bats do have some very interesting
adaptations.
They have highly specialized teeth.
Their front incisors are razor-sharp, so they
can give a quick swift cut, it's a little
bit like a paper cut, where you can barely
feel it but it bleeds and bleeds.
They have a grooved tongue so that they don't
have to actively lick up the blood; the blood
will run by capillary action right up into
their mouth.
And there's a number of drug companies studying
the fact that they have anticoagulant in their
saliva.
So normally when a cut forms, it'll immediately
start to clot up, but they have proteins in
their saliva that keeps that from happening.
Now most animals sleep through a vampire bat
attack, so they don't fly at your throat and
try and suck your blood.
Instead, like this bat down here, they've
taken a little bite on the hoof of a donkey,
they’re feeding, the donkey is probably
sleeping through this whole thing.
So it's not this massive, violent attack.
It can be dangerous though because they can
deplete blood supply and they can also spread
blood-borne diseases.
Of the three different kinds of vampire bats,
two are endangered and not doing well as we
continue to cut down rain forest.
The third species is actually increasing because
they really like cattle, and so as we cut
down rain forest for a cheap grazing ground
for cattle, these particular vampire bat populations
are increasing.
So researchers have done taste tests - vampire
bats don't really prefer human blood, they
prefer cattle and chickens, different kinds
of birds especially.
So my advice regarding vampire bats is don’t
go to Central America and sleep outside naked
and you'll probably be okay!
What do most bats eat?
Insects.
This graph shows you what a majority of bats
eat, mostly insects.
Another large group are fruit eaters.
Some are going to feed exclusively on nectar.
And then we have the small individuals, we
have the blood feeding bats, we also have
fishing bats, and there's a few that will
eat small mice and frogs.
All the bats we have around here are insectivores.
If you get into the very, very southern tip
of California, down in San Diego, there are
a few nectar feeding bats down there.
Another myth is that bats are pests, and I
think this goes with “well, if their rats
they must be pests” and they're not rats.
In fact, bats eat pests more than they are
pests.
The Mexican free tailed bats feeding over
Texas eat 250 million tons of insects every
year!
That is a crazy amount of insects.
It turns out the Gulfstream will pick up insects
down in Mexico and blow them up over Texas
and then they drop down right there, and so
there's a huge number of insects and there's
lots of agriculture.
And so this actually makes farmers in Texas
the number one advocates for bat conservation,
because eating 250 million tons of insects
is a lot of pesticides you don't have to spray.
Bats are also really important pollinators
and seed dispersers.
When you cut down an acre of rainforest, 90%
of the plants that regrow, regrow because
a bat dropped a seed there.
It's a perfect kind of seed dispersal for
plants - they eat the fruit, the fruit passes
through, it drops with a little packet of
fertilizer, and starts to grow.
They also are really important pollinators
for a number of different species.
The one that college students are usually
most familiar with is the agave cactus.
Bats are the sole pollinators of the agave
cactus, so the only way we’re going to continue
to have more agave cactus is to have bat pollinators,
and if you don't know already, agave cactus
is what you make tequila from.
So next time you have a margarita, toast a
bat.
And then finally bat guano is an excellent
fertilizer, especially from bats that primarily
eat insects, that makes their droppings full
of nitrogen, and when you want good fertilizer,
you want fertilizer that has lots of nitrogen.
So in some places, it's actually a career
to go into caves and harvest guano and sell
it.
You can buy bat guano at local nurseries,
and it's quite expensive, it'll be $10 a pound,
something like that.
There is a Kiwi farmer in the Fairfield area
who was a huge barn that's been taken over
by bats and he has let them have it, and he
goes in once or twice a year and harvests
the guano, and he swears that he's Kiwis are
better than everyone else's because of that
bat guano.
