Brown researchers have shed light for the first time on how bats perform the acrobatics necessary to land with their feet above their heads.
The research, published in the Journal of Experimental Biology earlier this month, shows that landing styles varied among species: Two species studied cart-wheeled into a softer landing, while a third back-flipped into a harder impact and landed on all fours. Daniel Riskin, a postdoctoral researcher in the Department of Ecology and Evolutionary Biology who was the study's lead author, said the differences in landing styles may be due to evolutionary differences between the bats.
A broad aim of his research was to shed light on the function of bats' unique body shape - the mammals have skinny, long legs that are well-suited to flying and roosting, but could be at risk of injury during forceful landings, Riskin told The Herald.
Associate Professor of Biology Sharon Swartz and Professor of Engineering Kenneth Breuer assisted Riskin's study, providing funding, personnel and access to the animals for the research. The research team used bats housed in the basement of the BioMedical Center and at the University of Maryland.
High-speed digital cameras captured the bats' landings, and a scale attached to the lab's ceiling measured the force of their impacts. The research took advantage of bats' natural tendency to choose a favorite roosting spot in a given enclosed space and keep returning to it, Riskin said.
The slow-motion videos of the bats' landings, which Riskin has posted on his personal Web site, show bats swooping toward their perches, then - depending on their species - either turning or flipping upside-down before clasping onto a plastic grate.
Data from the videos were used to generate graphs of the bats' movement during landing - with specific measurements of the animals' pitch, yaw and roll - Riskin said.
The species that landed significantly harder than the other two, and with four points of contact rather than two, was Cynopterus brachyotis, which typically roosts in trees. The softer landers were closer evolutionary cousins, Riskin said, that usually roost in rocky caves.
"A species seems to have a way of landing," he said. "You can ask why some species have that character, and others have a different character. ... I think the answer to that is that bats that roost in foliage can land as hard as they want - it won't hurt."
If they landed as forcefully as their tree-dwelling relatives, cave-roosters would risk a hazardous collision of their fragile hind legs with the rock ceiling.
Riskin said he wants to repeat the landing experiments with more bat species from South America, which is home to a wide variety of bats with different feeding and roosting habits. This further study could lead to a better understanding of how differences in bat species have evolved over time, he said, and would test the idea, suggested by his initial research, that bats roosting in caves land more softly.
"I certainly have not proven anything yet," Riskin said.
But Riskin's interest in bats extends beyond their acrobatic capabilities.
"In museums, you might have one species of bat in the mammals section," said Riskin, who has travelled around the world to study the animals. "In truth, one-fifth of mammals are bats."
"If you're interested in diversity, if you're interested in the variation of animal body plans ... bats are a great system (to study) because there are so many different kinds," he said.
Riskin enjoys seeking out and studying species of bats he hasn't encountered before, he added, because they always present "variations on the theme" of typical bat behaviors. His next research project may lead him to Madagascar, where a species of bat only recently found in significant numbers uses adhesive pads to affix itself to smooth surfaces, even glass.
