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Holy Echolocation! How Bats Got Their Amazing Superpowers

Updated on February 12, 2012
In case you were wondering why they're called microbats.
In case you were wondering why they're called microbats. | Source

Phylogenically speaking, we live on a bat-planet. With more than 1,240 species in the order Chiroptera, these winged creatures account for one-fifth of all mammal species and occupy every continent in the world but Antarctica. Contrary to popular belief, bats are not closely related to rodents, birds, or insects, and occupy a distinct branch of the mammalian tree.

Reconstructing the evolutionary history of bats is rather difficult, as their delicate bones do not fossilize well and thus there are few early bat and proto-bat specimens in the fossil record. This also makes it rather difficult to determine how and when bats acquired the abilities of flight and echolocation, leading some in the anti-science community to cite this as proof of special creation.

The fact-based version of events, while more complicated, is far more interesting.

Eptesicus fuscus, commonly known as the big brown bat - an insectivorous microbat indigenous to the eastern United States
Eptesicus fuscus, commonly known as the big brown bat - an insectivorous microbat indigenous to the eastern United States | Source
A guano-load of pteropus poliocephalus at the Royal Botanic Gardens in Sydney, Australia. Commonly known as the grey-headed flying fox, this megabat feeds on fruit, nectar, and pollen.
A guano-load of pteropus poliocephalus at the Royal Botanic Gardens in Sydney, Australia. Commonly known as the grey-headed flying fox, this megabat feeds on fruit, nectar, and pollen. | Source
A Rhinolophus hipposideros microbat in France, just hanging around the cave doing rhinolophusy hipposiderosy things.
A Rhinolophus hipposideros microbat in France, just hanging around the cave doing rhinolophusy hipposiderosy things. | Source

A Complicated Bat-Taxonomy

The order Chiroptera is split into two suborders - Megachiroptera or megabats and Microchiroptera or microbats - in traditional Linnaean taxonomy. While all bat species are capable of flight, only the microbats (and one genus of megabats) are capable of echolocation. Megabats are also generally eat fruit, nectar, and pollen, while microbats are insectivorous or blood-sucking in addition to eating fruit. As the name implies, microbats are generally smaller (though not always) and have a few other physical distinctions from megabats, such as a missing claw on the second toe of their forelimb and a lack of insulating underfur.

Research using comparative anatomy and molecular genetic evidence has indicated that both suborders evolved from a common ancestor that already had capability of flight. How these proto-bats diverged into the branches we have today is a subject of much debate in chiroptologic circles. A proposal based on cladistic analysis - and supported by genetic evidence - would split the bat order into the suborders Yinpterochiroptera and Yangochiroptera. The Yinpterochiropteran suborder would include most of the current megabat families and a handful of current microbat families. The Yangochiropteran suborder would include all bats who use laryngeal echolocation - generating ultrasonic pulses in the voicebox rather than using a tongue click.

Same Bat-Timing, But Different Bat-Channels

Microbats generate sounds in the 14,000Hz to 100,000Hz range, and at intensities up to 140 decibels - as loud as a pistol firing or a jet engine. Different bat species use different sound frequencies depending on their environment, hunting technique, and type of prey. Some bats use constant frequencies during a hunt, others sweep through a range of sound frequencies, and still others produce multiple harmonics in their echolocation calls.

Constant frequencies are useful when hunting in open environments, allowing the bat to determine the range and velocity of more distant targets by subtle changes in Doppler shift. On the other hand, a sweep of frequencies (frequency modulation) is best for close and cluttered environments such as caves, as the multiple frequencies prevent call and echo from overlapping and allow the bat to easily distinguish moving targets from background noise.

In general, the timing of echolocation calls follows a standard pattern across microbat species. During the initial search phase, sounds are produced at a slow rate of ten to twenty per second. As a target is identified, the rate of sound pulses increases - often with an increase in sound intensity. On final approach, the rate of calls can be as high as 200 pulses per second - known as the terminal buzz.

Echolocating bats have precisely tuned inner ear organs, allowing them to hear the echoed ultrasonic pulses with extreme precision. Microbats also have a comparatively larger auditory cortex than other mammals, reflecting the importance of this sense to their survival. Hunting bats use the slight timing differences between sounds received in both ears to locate the direction of the target prey, and it is hypothesized that they use echoes from the tragus (the flap of skin in front of the ear canal) to determine the elevation of the target.

Paleogeographic reconstruction of the Earth in the Eocene period 50 million years ago.
Paleogeographic reconstruction of the Earth in the Eocene period 50 million years ago. | Source

Some Days You Just Can't Get Rid of An Allele

There are several competing hypotheses for how and when bats evolved their abilities of flight and echolocation. Although some studies from the 1980s seemed to indicate that the megabat species evolved from a shared ancestor with primates, most current genetic evidence indicates that bats likely evolved from an earlier flying mammal 52 to 54 million years ago and later split into the Yinpterochiroptera and Yangochiroptera lines.

Until recently, there had been some debate over whether flight or echolocation had evolved first in the chiropteran lineage. However, discovery of the Onychonycteris finneyi fossil in the Green River Formation of the midwestern United States seems to have resolved this debate, as the fossil was capable of flight but did not appear to have the cochlear structure necessary for echolocation.

Where laryngeal echolocation fits into this lineage complicates the bat family tree. There are currently two competing hypotheses. One hypothesis is that echolocation evolved once in microbats, then was lost in the pteropid line and later regained in the Egyptian Rousettus bat, which uses tongue-clicks rather than laryngeal sounds to locate prey. A second hypothesis is that echolocation evolved separately in the Rhinolophoidea superfamily and the Yangochiropteran bats. Genetic analysis so far points to the single-origin hypothesis.

The bat lineage is further complicated by the geographic distribution of bat families. Genetic evidence hints that bats likely evolved in tropical regions of Laurasia or Africa and spread via land bridges to South and North America. However, fossil evidence of early bats is lacking in Africa and South America, and reconstruction of the geographic radiation of bats is difficult without further bat-discoveries.

The differing strategies of echolocation used by bat species in different environments offers one of the best examples of adaptive radiation in the natural world. Coevolution also plays a part, as moths and other prey species have adopted "jamming" techniques to counteract bat echolocation calls in some ecosystems.

Although there are many unanswered questions in the lineage of bat evolution and many holes in the fossil record, genetic evidence from modern bats has produced a strong working model of the lineage of these fascinating creatures.

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    • John Sarkis profile image

      John Sarkis 5 years ago from Los Angeles, CA

      Interesting hub. I did not know we live in a "bat planet." I thought there were only 2-3 species of bats around---thats it! Learned something new everyday.

      John

    • TFScientist profile image

      Rhys Baker 5 years ago from Peterborough, UK

      I too was unaware of the sheer volume of bat species...but surely by that logic we live on a beetle, or wasp...or perhaps bacteria planet? :) Loved the explanation of the development of echolocation, and any hub with a classic batman clip is alright by me.

      Voted up, interesting and shared. Thanks!

    • profile image

      jenubouka 5 years ago

      Awesome information, I did not know many things about the extensive background of bats. I have to take my girly side for a moment and say how adorable and frightening these little creatures are, especially the micro-bat.

    • davenmidtown profile image

      David Stillwell 5 years ago from Sacramento, California

      Very nicely put together, easy to read, bridged explanations and full of good information. I think there are 800,000 species of beetles and then some... which is probably because bats don't normally eat beetles? Voted up and awesome.

    • scottcgruber profile image
      Author

      scottcgruber 5 years ago from USA

      Thank you all very much for the comments! And while it's true that if measured by weight and/or volume we probably live on a beetle or bacteria planet (according to a recent study our bodies contain about ten times more bacteria cells than human cells) it's much more fun to say "bat-planet."

    • Austinstar profile image

      Austinstar 5 years ago from Somewhere in the universe

      Whoa! You really know your bats! And I live in "Bat City". I have been told that Austin, Texas has the largest urban bat colony in the U.S. if not the world. A few million Mexican Free Tailed bats have colonized the under structure of our Congress Avenue bridge. It's a great show!

    • Teresa Coppens profile image

      Teresa Coppens 5 years ago from Ontario, Canada

      Awesome hub and packed full of well written, interesting information. I'm grateful for the bats that live around my farm here in Ontario as they help keep down the mosquito and bug population. I didN't know there were bats that did not echo locate. Great job!

    • scottcgruber profile image
      Author

      scottcgruber 5 years ago from USA

      Wow! That's a guano-load of bats! Mexican free tailed bats are among the echolocators who use frequency modulation when they locate prey. Neat, huh?

    • scottcgruber profile image
      Author

      scottcgruber 5 years ago from USA

      Thank you very much! I hadn't known that either before researching this hub. Interesting, isn't it?

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