do bats have hollow bones like birds

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If you’ve ever been stuck upside down on a rollercoaster–or seen those who have been in this unfortunate position–you probably wonder why any creature would voluntarily hang from its feet. But for bats, being upside down is a convenient and useful way to roost.

While some other mammals—like flying squirrels and sugar gliders—can soar across the sky, bats are the only mammals that can truly fly. When you’re a bat that might want to fly at any minute—whether to snatch a tasty insect out of the sky, grab a drink of water on the wing, or escape a predator—hanging by your feet makes it easy to take flight. Simply let go, and you’re instantly airborne. Hanging upside down in hard-to-reach locations is also a handy way to dodge predators when you’re dangling far out of their reach.

For bats, hanging is also easy. When humans hang from, say, a chin-up bar, it takes a great amount of effort to clutch the bar and dangle, whether upside down or right-side up. People quickly tire from a hanging position. Bats don’t have to expend nearly as much effort to hang since the tendons and ligaments in their legs and feet help aid the process.

Bats’ ancestors were mammals that glided through the air, but modern day bats have evolved to be able to fly. However, unlike birds that have hollow bones—including some that are “pneumatized” with air pockets to make them even lighter—bats do not have hollow bones. This means that bats need to reduce weight in other ways to be able to take flight. Their long bones, like femurs, are light so they can fly, and because of this, they can’t withstand the compression standing up. In 1977, D.J. Howell and Joe Pylka published a paper in the Journal of Theoretical Biology delving into this issue. They found that most bats’ leg bones “cannot withstand compression stress,” so “hanging is advantageous.” Bats also have skin membranes that spread out between their light, elongated fingers and ankles, which is great for flying, but makes it difficult to sit or stand.

While many bats can still take flight from the ground, already being in the air—dangling from their toes while grasping their perch with their claws—makes going airborne effortless.

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do bats have hollow bones like birds

Human, Bird, and Bat Bone Comparison

Bat, bird, and human arms all appear quite different from the outside. The skin of humans, the feathers of birds, and the hair of bats are all covered. However, the insides of the forearms of humans, birds, and bats are remarkably similar. Given that humans, birds, and bats all descended from a common ancestor, it is noteworthy that all three of these organisms share the same types of forearm bones.

The forearm bones of humans, birds, and bats are the humerus, ulna, radius, carpals, metacarpals, and phalanges. Can you identify these bones on the diagram below?.

Despite having similar basic bone types, these organisms’ bones have been altered to serve various purposes. People use their forearms to play the piano, swing a baseball bat, and reach and pick up objects. Forearms on bats and birds have developed into wings that enable them to soar. Are there any other distinctions or parallels between the forearms of humans, birds, and bats?

Download your own human, bird and bat bone coloring page.

Animal bones are robust and typically dense, but their structural makeup varies. Birds’ bones are much more void inside than human bones are. Moreover, compared to human bones, bird and bat bones appear smaller and more delicate. This was supposed to lighten the bones of bats and birds so they could fly. Some recent research has shown this may not be true. Bat and bird bones are thinner and contain more empty space than those of most mammals, but the bone material in both species is actually denser than that of a rodent of comparable size. According to the research, these bones merely appear to be lighter. Rather, to withstand the strain of flight, their greater bone density makes them robust and rigid. It appears that birds have the densest bone density, followed by bats and non-flying mammals.

Are bird bones hollow? Yes they are. But unlike a pipe, a bird’s bone structure does not consist of a single large opening. Rather than being solid, bird bones are lighter due to their large air pockets. The bones’ internal structure adds to their strength.

Reference:

Elizabeth R. Dumont. (June 10, 2010). Bone density and the lightweight skeletons of birds. Proceedings of The Royal Society B Biological Sciences. Retrieved April 18, 2015 from https://royalsocietypublishing.org/doi/full/10.1098/rspb.2010.0117

Even though many bats can still fly from the ground, it is much easier to get airborne once they are in the air, hanging from their toes and using their claws to hold onto their perch.

For bats, hanging is also easy. It takes a lot of work for humans to grip a bar when they are hanging, say, chin-up bar, and to hang either upside down or right-side up. People quickly tire from a hanging position. Because of the tendons and ligaments in their legs and feet, bats don’t need to use as much energy to hang.

Bats’ ancestors were mammals that glided through the air, but modern day bats have evolved to be able to fly. However, unlike birds that have hollow bones—including some that are “pneumatized” with air pockets to make them even lighter—bats do not have hollow bones. This means that bats need to reduce weight in other ways to be able to take flight. Their long bones, like femurs, are light so they can fly, and because of this, they can’t withstand the compression standing up. In 1977, D.J. Howell and Joe Pylka published a paper in the Journal of Theoretical Biology delving into this issue. They found that most bats’ leg bones “cannot withstand compression stress,” so “hanging is advantageous.” Bats also have skin membranes that spread out between their light, elongated fingers and ankles, which is great for flying, but makes it difficult to sit or stand.

There are other mammals that can fly, such as sugar gliders and flying squirrels, but bats are the only ones that can actually fly. Hanging by your feet makes it easy to take off when you’re a bat that might want to take off at any moment, whether it’s to escape a predator, snag a drink of water on the wing, or take down a tasty insect. Simply let go, and you’re instantly airborne. Another useful tactic to avoid predators when you’re hanging far out of their reach is to hang upside down in difficult-to-reach places.

If you’ve ever seen someone else or yourself upside down on a roller coaster, you’ve probably wondered why any living thing would choose to hang from its feet. However, bats find that lying upside down is a practical and useful way to roost.

FAQ

Do bats have bones like birds?

Bats, like birds, also have fused cranial bones for additional lightness. Like most birds and pterosaurs, bats have a keel on the sternum, or breastbone, to which the large flight muscles attach.

How can you tell bats from birds?

Size – Our bats are small; larger than a Robin is probably a bird. Flight Pattern – Bats fly more erratically than birds, who will swoop and dive but fly in straighter lines. Bats zig and zag while chasing insects. Wings – Bat never stop flapping their wings!

Are birds the only animals with hollow bones?

This bone specialization isn’t found only in birds. Fossils show evidence of air pockets in carnivorous dinosaur bones. Humans have hollow bones around their sinuses. They can also be found in the skulls of other mammals and crocodiles.

What are the skeletal similarities between a bat and a bird?

They have the same basic skeletal structure, inherited from their common tetrapod ancestors. Both have a skull, vertebrae, front and rear limbs, and a pelvis. There are some differences in the bones themselves, as birds have hollow bones, and air sacs that are part of the respiratory system.