It’s that time of year again when a small patch of “mushitu”
evergreen forest in northern Zambia receives the world’s biggest
gathering of Fruit Bats. Quite why so many of these Straw-coloured
Fruit bats, Eidelon Helvum, congregate in one group for two
months every year is still a mystery.
The mammal books will tell you that this is a sociable species
occurring in colonies of up to a few hundred thousand, but the
Kasanka spectacle has been consistently estimated to be between 5
and 20 MILLION individuals. The sheer number and the fact
that they are observed to arrive and depart in distinct groups over
a couple of weeks, clearly shows that this is not one roaming colony
but a gathering of many. Visitors lucky enough to be in Kasanka at
this time always have the same two questions.
1. Where do these bats come from and where do they go?
2. Why do so many bats all come to this one little spot in Zambia?
Over the past seven years most of the world’s top bat Scientists
have been to Kasanka but they have failed to come up with conclusive
answers to these questions. The person who has put the most time and
effort into the Kasanka bats is Heidi Richter, an American
scientist, who is now working on a PhD following her MSc two years
ago. We first met Heidi on the side of the road in Chisamba when she
was a Peace Corps volunteer looking for a lift! At the time we
already had a Brown necked Parrot in the car which we had
confiscated from the roadside “sellers” and so a biology student
seemed a useful addition to the passenger manifest. When we started
chatting, we found out she was one of a growing group of biologists
around the world who are obsessed with bats and that was the start
of Heidi’s involvement in the Kasanka bats.
This year we are hoping to make some real progress on the first big
questions of where they come from and where they go, because Heidi
has secured enough funding to fit four minature GPS satellite
transmitters. When this method was first proposed in 2000, it was
not only the considerable cost that had to be overcome, but the fact
that the lightest units available which would last for twelve months
were then were still too heavy to be fitted to these bats. Hence we
have had to wait some years for technology to catch up with our
ambitions. Bats are not as strong flyers as birds and so the
recommended percentage of body weight for any device to be attached
is less. Indeed bats have quite a few limitations due to their
relatively late evolution into flight. It’s said that these bats
cannot fly in the sun as they overheat! As long as the satellite
tracking goes according to plan we should get some idea of where the
bats disperse to feed each night and where they spend the rest of
the year. We’ll be posting updates on the Kasanka website (www.kasanka.com).
Ideally we would like to collar about 20 or 30 bats next year to get
an idea of the full range of the bats but that will depend on the
success of this year’s trial and finding the funds!
The second question of why so many bats should all come to one place
remains a mystery. An early theory was that it was a gene exchange
but the colonies have been observed to be at all different stages of
the breeding cycle, with some mating, some in early pregnancy, some
late, some with young. It’s known from observation of individual
colonies around Africa that these bats are very seasonal and
synchronised in breeding, so the diversity seen in Kasanka implies
that they are coming from a wide area. These bats are mainly
recorded around the edge of the Equatorial rainforest, but no-one
yet knows if large colonies live deep inside the rainforest, so the
satellite tracking research may reveal interesting information on
the species as a whole. Another theory that still needs looking at
is that the Kasanka area offers a “super-abundance” of fruit in
November and December which is just too good to miss out on. Yet
another theory is that fruit around Kasanka contains some vital
minerals which the bats need. More work is definitely needed on this
burning question.
You may ask why scientists and ecologists are so interested in these
unusual mammals. The answer is that fruit bats are known to be by
far the most important dispersers of seed for the forests, and their
health is therefore linked to the survival of the world’s great
rainforests. Against this, observations have shown that fruit bat
numbers are in serious decline in many places, due to loss of
habitat and hunting for food. Luckily, the Lala people living around
Kasanka do not consider roast bat a delicacy as do their distant
relations in West Africa!
There are a lot of other fascinating aspects of the Kasanka bat
colony, such as their relation with the small forest they roost in.
As well as dropping huge amounts of fertilizer they also pull off
large branches with the sheer weight of hanging bat! Predators like
birds of prey, crocodiles, bushpigs, snakes and even the odd leopard
are all observed “swarming” in for easy meals!
One thing remains certain. The sight of these bats flying out of the
forest to forage at sunset is one of Africa’s great wildlife
spectacles, which can only be appreciated when seen in person. Treat
yourself to a visit to Kasanka any time before Christmas and you
won’t be disappointed! It’s also a great time for birds, flowers,
butterflies and game viewing. Bookings can be made through travel
agents or by email to
wasa@kasanka.com The lodges in Kasanka are open all year.
Edmund Farmer is the Park Manager at Kasanka National Park.
November
2005
Over the past seven years most of the world’s top bat Scientists
have been to Kasanka but they have failed to come up with conclusive
answers to these questions. The person who has put the most time and
effort into the Kasanka bats is Heidi Richter, an American
scientist, who is now working on a PhD following her MSc two years
ago. We first met Heidi on the side of the road in Chisamba when she
was a Peace Corps volunteer looking for a lift! At the time we
already had a Brown necked Parrot in the car which we had
confiscated from the roadside “sellers” and so a biology student
seemed a useful addition to the passenger manifest. When we started
chatting, we found out she was one of a growing group of biologists
around the world who are obsessed with bats and that was the start
of Heidi’s involvement in the Kasanka bats.
This year we are hoping to make some real progress on the first big
questions of where they come from and where they go, because Heidi
has secured enough funding to fit four minature GPS satellite
transmitters. When this method was first proposed in 2000, it was
not only the considerable cost that had to be overcome, but the fact
that the lightest units available which would last for twelve months
were then were still too heavy to be fitted to these bats. Hence we
have had to wait some years for technology to catch up with our
ambitions. Bats are not as strong flyers as birds and so the
recommended percentage of body weight for any device to be attached
is less. Indeed bats have quite a few limitations due to their
relatively late evolution into flight. It’s said that these bats
cannot fly in the sun as they overheat! As long as the satellite
tracking goes according to plan we should get some idea of where the
bats disperse to feed each night and where they spend the rest of
the year. We’ll be posting updates on the Kasanka website (www.kasanka.com).
Ideally we would like to collar about 20 or 30 bats next year to get
an idea of the full range of the bats but that will depend on the
success of this year’s trial and finding the funds!
The second question of why so many bats should all come to one place
remains a mystery. An early theory was that it was a gene exchange
but the colonies have been observed to be at all different stages of
the breeding cycle, with some mating, some in early pregnancy, some
late, some with young. It’s known from observation of individual
colonies around Africa that these bats are very seasonal and
synchronised in breeding, so the diversity seen in Kasanka implies
that they are coming from a wide area. These bats are mainly
recorded around the edge of the Equatorial rainforest, but no-one
yet knows if large colonies live deep inside the rainforest, so the
satellite tracking research may reveal interesting information on
the species as a whole. Another theory that still needs looking at
is that the Kasanka area offers a “super-abundance” of fruit in
November and December which is just too good to miss out on. Yet
another theory is that fruit around Kasanka contains some vital
minerals which the bats need. More work is definitely needed on this
burning question.
You may ask why scientists and ecologists are so interested in these
unusual mammals. The answer is that fruit bats are known to be by
far the most important dispersers of seed for the forests, and their
health is therefore linked to the survival of the world’s great
rainforests. Against this, observations have shown that fruit bat
numbers are in serious decline in many places, due to loss of
habitat and hunting for food. Luckily, the Lala people living around
Kasanka do not consider roast bat a delicacy as do their distant
relations in West Africa!
One thing remains certain. The sight of these bats flying out of the
forest to forage at sunset is one of Africa’s great wildlife
spectacles, which can only be appreciated when seen in person. Treat
yourself to a visit to Kasanka any time before Christmas and you
won’t be disappointed! It’s also a great time for birds, flowers,
butterflies and game viewing. Bookings can be made through travel
agents or by email to