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Muscle Power: Bats Power Take-Off Using Recycled Energy

July 5, 2013 — Bats are uniquely able to stretch and store energy in their bicep and tricep tendons during take-off and climbing flight, giving them an extra power boost. A new study on fruitbats, to be presented at the meeting of the Society for Experimental in Valencia on July 4, used cutting edge technology to image how these small mammals move through the air.
Dr Nicolai Konow (Brown University, USA), who led the research said: "Energy is stored in the triceps tendon, which is used to power elbow extension -- in essence, elbow extension happens using "recycled" energy. State of knowledge, and our results, indicates that bats are unique among small mammals in stretching their tendons, as small mammal limb tendons are thought to be too thick and stiff to be stretched."
"By combining information about skeletal movement with information about muscle mechanics, we found that the biceps and triceps tendons of small fruitbats are stretched and store energy as the bat launches from the ground and flies vertically."
The researchers used a cutting edge 3D imaging technology called XROMM (X-ray Reconstruction of Moving Morphology) that allows visualizing rapid internal skeletal movement. XROMM combines 3D models of bone morphology with movement data from biplanar x-ray video to create highly accurate re-animations of the 3D bones moving in 3D space. The researchers also used a novel method called fluoromicrometry, where small radio opaque markers are implanted directly into muscle, which allows measuring length change with high precision and accuracy during contractions.
These findings indicate that the action of muscles powering animal movements through fluids may be influenced by series elasticity, and that at least some limb tendons in small mammals can be stretched by muscular and aerodynamic forces, enabling force control of joint movement.
This research will likely have relevance for the development of autonomous micro aircrafts and potentially also amphibious search and rescue vehicles.

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Why Bats Are More Efficient Flyers Than Birds



Flexible, highly articulated wings give bats more options for flight than birds: more lift, less drag, greater maneuverability.
Credit: K. Breuer, Harvard University

Their motions might seem erratic and graceless, but bats are more efficient flyers than birds, thanks to an airlift mechanism that is unique among aerial creatures, new wind-tunnel tests show.

Previous studies that compared oxygen consumption among birds, insects and bats of similar sizes—a hummingbird, a small bat and a large moth, for example—found that bats [image] use less energy to fly, but “no one’s really had an explanation for this phenomenon,” said study team member Sharon Swartz, an associate professor in ecology and evolutionary biology at Brown University.

The wind tunnel tests suggest the secret to efficient bat flight lies in the furry creature’s flexible skin membrane and its many-jointed wings, which together creates a shape-shifting structure that provides more lift, less drag and greater maneuverability.

Like human hands

Unlike insects and birds, which have relatively rigid wings that can move in only a few directions, a bat’s wing contains more than two dozen joints that are overlaid by a thin elastic membrane that can stretch to catch air and generate lift in many different ways [video].

This gives bats an extraordinary amount of control over the three-dimensional shape their wings take during flight, Swartz explained.

“Insects can move the joint at the insect equivalent of a shoulder, but that’s the only place where they can exert force and control movement,” she said. Birds have many more joints in their wings, but it’s nothing compared to bats.

“Bats are operating with the same skeleton that we have. Every joint in the human hand is there in the bat’s wing and actually a couple more,” Swartz told LiveScience. “Think about the degree of control that we have over the shape of our hands—bats are able to extend that to make fine scale adjustments during flight.”

It was once thought that despite having so many wing joints, it was more efficient for bats to stabilize their wings and wave them up and down like relatively rigid paddles the way birds do.

“What we see when we look more closely is that in fact, it’s not what they’re doing,” Swartz said in a telephone interview. “It suggests that they’re able to take advantage of this highly jointed system to make subtle adjustments to the wing shape during flight.”

Stretchy wings

The other key to a bat’s efficient flight lies in its highly elastic wing. Videos from the wind tunnel tests show that a bat’s wing is mostly extended for the down stroke during straightforward flight. But because the membrane can curve and stretch much more than a bird’s wing can, bats can generate greater lift for less energy.

By blowing non-toxic smoke over the bats [video] as they were flying, the researchers were also able to create a video that revealed how air flows around the creatures as they flap their wings.

The data showed that during the down stroke, the air vortex—which generates much of the lift in flapping-wing flight—closely tracks the animals’ wingtips. But in the upstroke, the vortex appears to come from another location entirely, perhaps the wrist joint.

The researchers think this unusual pattern helps to make bat flight more efficient and credit it to the tremendous flexibility and articulation of the wing.

Model for flying machines

The findings, detailed in the Dec. 2006 issue of the journal Bioinspiration and Biomimetics, suggest the furry fliers might make good templates for flying machines.

“Bats have unique capabilities, but the goal is not to build something that looks like a bat,” said study team member Kenny Breuer, also of Brown University. “We want to understand bat flight and be able to incorporate some of the features of bat flight into an engineered vehicle.”

The complexity of bat’s wings also challenges some current theories that say bats evolved from some kind of flying squirrel-type creature.

“That might still be true, but what we know today is that although gliding appears to have evolved seven times in mammals,” Swartz said, “not a single one of those groups is closely related to bats.”

W.C.K.D

 

If you can't get big, get more. Why should bats need to change anything physically? Just develop pack hunting behaviour and the spectrals will have it made!

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Group Hunting—A Reason for Sociality in Molossid Bats?


Abstract

Many bat species live in groups, some of them in highly complex social systems, but the reasons for sociality in bats remain largely unresolved. Increased foraging efficiency through passive information transfer in species foraging for ephemeral insects has been postulated as a reason for group formation of male bats in the temperate zones. We hypothesized that benefits from group hunting might also entice tropical bats of both sexes to live in groups. Here we investigate whether Molossus molossus, a small insectivorous bat in Panama, hunts in groups. We use a phased antenna array setup to reduce error in telemetry bearings. Our results confirmed that simultaneously radiotracked individuals from the same colony foraged together significantly more than expected by chance. Our data are consistent with the hypothesis that many bats are social because of information transfer between foraging group members. We suggest this reason for sociality to be more widespread than currently assumed. Furthermore, benefits from group hunting may also have contributed to the evolution of group living in other animals specialized on ephemeral food sources.


http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0009012