Snakes cooperate to snag bats on the wing.
Snakes in a cave. I’m Bob Hirshon and this is Science Update.
Several years ago, scientists reported on some Cuban boa snakes that specialize in bat-hunting. The snakes hang from cave walls and ceilings and snag bats on the wing. Now, in the journal Animal Behavior and Cognition, University of Tennessee, Knoxville, zoologist Vladimir Dinets reports that the reptiles work in small teams, forming a bat-catching curtain of snakes.
They kind of make a fence across the cave entrance so the bats have nowhere to go, and they have to fly very close to the snakes, and snakes can catch them more easily.
In fact, while bats could evade a single dangling snake, when there were three of them, the bats sometimes bumped into them on their way through. As a result, snakes that worked together nearly always caught bats. And since there are many bats and the snakes can eat just one bat each, it’s more fruitful to cooperate than to compete. I’m Bob Hirshon, for AAAS, the science society.
Making Sense of the Research
When predators work together to capture prey it is considered cooperative hunting. This type of hunting involves predators hunting together in groups in which there is a division of labor and role specialization. For example, among Aplomado falcons, male and female falcons hunt together and they always perform the same task in every situation. They begin perched together and the males initiate and give a sharp “chirp” vocalization to signal for the female to follow suit. When chasing birds on the ground, the females follow right behind the birds in the bushes and the males swoop in from overhead to make the kill.
Only about 5-20% of carnivores participate in cooperative hunting, including lions, wild dogs, spotted hyenas, chimpanzees, some birds of prey, and humans. Most predators, however, are solitary and prefer to hunt alone. So you can imagine University of Tennessee, Knoxville, zoologist Vladimir Dinets' interest when he observed the behavior of these particular boas in a cave in Cuba. Dinets became interested in studying the hunting behavior of this particular species of snake, the Cuban boa, after he noticed their behavior when he was visiting the cave. He went back several times to watch what was going on.
For context, many Cuban caves shelter large colonies of bats. In some of those caves, small populations of snakes take advantage of the comings and goings of the bats to snatch them near the cave entrances.
In the cave studied by Dinets, he noticed that the boas hung down from the ceiling of the cave entrance and grabbed passing bats in midair. He found that if more than one boa was present, the snakes coordinated their positions in such a way that they could form a barrier across the entrance. This made it difficult or impossible for the bats to pass without getting within striking distance of at least one boa. “After sunset and before dawn, some of the boas entered the passage that connected the roosting chamber with the entrance chamber, and hunted by suspending themselves from the ceiling and grabbing passing bats,” wrote Dinets.
According to the study, these group hunts were always successful, and the more snakes were present, the less time it took each to capture a bat. But if there was only one boa, it sometimes failed to secure a meal.
Is this behavior by the Cuban boas actually cooperative hunting, though? According to Dinets, only a few of the world's 3,650 snake species have ever been observed hunting in the wild, so very little is known about snakes' diverse hunting tactics. In addition, only a handful of snakes have been observed to hunt in groups. Cooperative hunting among these snakes has never been proven.
More research will need to be conducted before the question can be answered.
Now try and answer these questions:
- What is cooperative hunting?
- What kinds of animals take part in cooperative hunting?
- What is the strategy of the Cuban boas when they try to catch bats?
- Do you think this is cooperative hunting? Why or why not?
This Science Update would be a great way to help engage your students in a unit on survival strategies that animals use. You could combine it with some of the other Science NetLinks resources listed below.