A Brown University-led research team has documented for the first time how bats land. The results are surprising: Not all bats land the same way. The findings, which appear in the Journal of Experimental Biology, could offer new insights into how the second-largest order of mammals evolved.

PROVIDENCE, R.I. [Brown University] — People have always been fascinated by bats, but the scope of that interest generally is limited to how bats fly and their bizarre habit of sleeping upside down. Until now, no one had studied how bats arrive at their daytime perches.

A Brown University-led research team is the first to document the landing approaches of three species of bats — two that live in caves and one that roosts in trees. What they found was surprising: Not all bats land the same way.

“Hanging upside down is what bats do,” said Daniel Riskin, a postdoctoral researcher in the Ecology and Evolutionary Biology department at Brown and lead author on a paper published in the Journal of Experimental Biology. “We've known this. But this is the first time anyone has measured how they land.”

Using sophisticated motion capture cameras in a special flight enclosure, the team filmed each species of bat as it swooped toward a latticed landing pad and landed on it. Cynopterus brachyotis, a tree-roosting bat common in tropical parts of southeast Asia, executed a half-backflip as it swooped upward to the landing site, landing as its hind legs and thumbs touched the pad simultaneously — a four-point landing, the group observed. The landing is hard, Riskin noted, with an impact force more than four times the species’ body weight.

The team then turned its attention to two cave-roosting species, Carollia perspicillata and Glossophaga soricina. These bats, common in Central and South America, approach their landing target with a vertical pitch and then, at the last instant, yaw to the left or to the right — executing a cartwheel of sorts — before grasping the landing pad with just their hind legs. The two-point landing is much gentler than the impact force exerted by the tree-roosting bats, the researchers observed; the cave-roosting bats have a landing impact force of just one-third of their body weight.

There are about 1,200 recognized bat species worldwide, so Riskin was cautious about not drawing any grand conclusions. Still, he said, the fact that the team has documented that bats land differently could open new insights into a species that makes up roughly one-fifth of all mammals on earth. “It's opening the door to how bats evolved,” Riskin said. “You can say that bats have been hanging upside down since they first evolved, and it has probably been one of the keys to their worldwide success.”

Other Brown researchers who worked on the paper include Sharon Swartz, associate professor of biology; Tatjana Hubel, a postdoctoral researcher; and Joseph Bahlman, a graduate student. John Ratcliffe, a biologist at the University of Southern Denmark, and Thomas Kunz, a biologist at Boston University, contributed to the paper.

Researchers have found what they say is some of the first unambiguous evidence that an animal other than humans can make spontaneous plans for future events. The report in the March 9th issue of Current Biology, a Cell Press publication, highlights a decade of observations in a zoo of a male chimpanzee calmly collecting stones and fashioning concrete discs that he would later use to hurl at zoo visitors.

"These observations convincingly show that our fellow apes do consider the future in a very complex way," said Mathias Osvath of Lund University. "It implies that they have a highly developed consciousness, including life-like mental simulations of potential events. They most probably have an 'inner world' like we have when reviewing past episodes of our lives or thinking of days to come. When wild chimps collect stones or go out to war, they probably plan this in advance. I would guess that they plan much of their everyday behavior."

While researchers have observed many ape behaviors that could involve planning both in the wild and in captivity, it generally hasn't been possible to judge whether they were really meeting a current or future need, he added. For instance, when a chimp breaks a twig for termite fishing or collects a stone for nut cracking, it can always be argued that they are motivated by immediate rather than future circumstances.

And that's what makes the newly described case so special, Osvath said. It is clear that the chimp's planning behavior is not based on a "current drive state." In contrast to the chimp's extreme agitation when throwing the stones, he was always calm when collecting or manufacturing his ammunition.

Osvath said he thinks wild chimps in general, as well as other animals, probably have the planning ability demonstrated by the individual described in the study. Indeed, experiments conducted recently with other captive chimpanzees have shown they are capable of making such plans. (Some have argued, however, that those findings could be the result of experimental artifacts.)

"I think that wild chimpanzees might be even better at planning as they probably rely on it for their daily survival," Osvath said. "The environment in a zoo is far less complex than in a forest. Zoo chimps never have to encounter the dangers in the forest or live through periods of scarce food. Planning would prove its value in 'real life' much more than in a zoo."