There could be twice as many bird species as we thought. So say researchers from the American Museum of Natural History, who argue in a new study <a href="http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0166307">published</a> in the journal PLOS ONE that birds have been greatly underrepresented, taxonomically speaking. Typical numbers for the total number of bird species worldwide tend to center around a range of 9,000 to 10,000, but the museum's scientists say that number is likely closer to 18,000. Of course, that begs the question: How could science be so far off? The researchers say it's all about how birds have been placed in various species. Bird species counts, they say, center around an idea known as the "biological species concept," in which species are defined based on which animals breed together. "It's really an outdated point of view," <a href="https://www.eurekalert.org/pub_releases/2016-12/amon-nsd121216.php">said</a> the study's lead author George Barrowclough in a statement, "and it's a concept that is hardly used in taxonomy outside of birds." <a href="http://www.seeker.com/extinct-bird-not-seen-since-1941-suddenly-reappears-1769588972.html">RELATED: 'Extinct' Bird Not Seen Since 1941 Suddenly Reappears</a> Barrowclough and his colleagues used different metrics to assign species, based instead on physical characteristics such as plumage and color. They studied a random sampling of 200 species through that framework and discovered that within that group there were almost two new species for each bird they examined. Extending that ratio out to the entire bird population, the researchers suggest that there may be roughly double the number of bird species in the sky. Going forward, the scientist say bird species assessments should take into account physical characteristics as well as genetic data. The counts matter, they say, because individual species are the benchmark used in conservation. "We really need to be clear about what a species is, how many there are, and where they're found," said study co-author Robert Zink. "This new number says that we haven't been counting and conserving species in the ways we want," added co-author Joel Cracraft. WATCH VIDEO: How Can Birds Sleep While They're Flying?

There could be twice as many bird species as we thought.

So say researchers from the American Museum of Natural History, who argue in a new study <a href="http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0166307">published</a> in the journal PLOS ONE that birds have been greatly underrepresented, taxonomically speaking.

Typical numbers for the total number of bird species worldwide tend to center around a range of 9,000 to 10,000, but the museum's scientists say that number is likely closer to 18,000.

Of course, that begs the question: How could science be so far off? The researchers say it's all about how birds have been placed in various species. Bird species counts, they say, center around an idea known as the "biological species concept," in which species are defined based on which animals breed together.

"It's really an outdated point of view," <a href="https://www.eurekalert.org/pub_releases/2016-12/amon-nsd121216.php">said</a> the study's lead author George Barrowclough in a statement, "and it's a concept that is hardly used in taxonomy outside of birds."

<a href="http://www.seeker.com/extinct-bird-not-seen-since-1941-suddenly-reappears-1769588972.html">RELATED: 'Extinct' Bird Not Seen Since 1941 Suddenly Reappears</a>

Barrowclough and his colleagues used different metrics to assign species, based instead on physical characteristics such as plumage and color. They studied a random sampling of 200 species through that framework and discovered that within that group there were almost two new species for each bird they examined.

Extending that ratio out to the entire bird population, the researchers suggest that there may be roughly double the number of bird species in the sky.

Going forward, the scientist say bird species assessments should take into account physical characteristics as well as genetic data.

The counts matter, they say, because individual species are the benchmark used in conservation. "We really need to be clear about what a species is, how many there are, and where they're found," said study co-author Robert Zink.

"This new number says that we haven't been counting and conserving species in the ways we want," added co-author Joel Cracraft.

WATCH VIDEO: How Can Birds Sleep While They're Flying?

There could be twice as many bird species as we thought.So say researchers from the American Museum of Natural History, who argue in a new study <a href="http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0166307">published</a> in the journal PLOS ONE that birds have been greatly underrepresented, taxonomically speaking.Typical numbers for the total number of bird species worldwide tend to center around a range of 9,000 to 10,000, but the museum's scientists say that number is likely closer to 18,000.Of course, that begs the question: How could science be so far off? The researchers say it's all about how birds have been placed in various species. Bird species counts, they say, center around an idea known as the "biological species concept," in which species are defined based on which animals breed together."It's really an outdated point of view," <a href="https://www.eurekalert.org/pub_releases/2016-12/amon-nsd121216.php">said</a> the study's lead author George Barrowclough in a statement, "and it's a concept that is hardly used in taxonomy outside of birds."<a href="http://www.seeker.com/extinct-bird-not-seen-since-1941-suddenly-reappears-1769588972.html">RELATED: 'Extinct' Bird Not Seen Since 1941 Suddenly Reappears</a>Barrowclough and his colleagues used different metrics to assign species, based instead on physical characteristics such as plumage and color. They studied a random sampling of 200 species through that framework and discovered that within that group there were almost two new species for each bird they examined.Extending that ratio out to the entire bird population, the researchers suggest that there may be roughly double the number of bird species in the sky.Going forward, the scientist say bird species assessments should take into account physical characteristics as well as genetic data.The counts matter, they say, because individual species are the benchmark used in conservation. "We really need to be clear about what a species is, how many there are, and where they're found," said study co-author Robert Zink."This new number says that we haven't been counting and conserving species in the ways we want," added co-author Joel Cracraft.WATCH VIDEO: How Can Birds Sleep While They're Flying?

Frigatebirds, an aquatic bird with a six-foot wingspan, can spend weeks at a time up in constant flight, up in the clouds. How is that even possible? As <a href="http://www.seeker.com/community/trace_dominguez" target="_blank">Trace Dominguez</a> explains in today's DNews report, the birds sleep with one eye open. Literally.Earlier this year, scientists from the <a href="http://www.orn.mpg.de/en" target="_blank">Max Planck Institute for Ornithology</a> in Germany fitted several frigatebirds with small EEG monitoring devices that measure brain waves. Then they cut the birds loose and recording data over 10 days while their feathered test subjects flew, nonstop, more than 3,000 kilometers.The results were <a href="http://www.sciencealert.com/scientists-have-just-seen-birds-sleep-while-flying-for-the-first-time-ever" target="_blank">pretty amazing</a>. It appears that frigatebirds sleep in the air by resting their brain for short durations -- one hemisphere at a time. In other words, they sleep with one eye open, while still flying. Data suggest the birds typically circle upward on air currents in the direction of their open eye, which is the one connected to the awake hemisphere. The Planck Institute researchers think they do this to watch where they're going and so they don't run into other birds.<a href="http://www.seeker.com/birds-fly-faster-as-flocks-get-bigger-1975344655.html" target="_blank">RELATED: Birds Fly Faster as Flocks Get Bigger</a>Actually, frigatebirds are not the only animal that sleeps half a brain at a time. It's a documented but unusual rest pattern called <a href="http://www.reed.edu/biology/professors/srenn/pages/teaching/web_2006/DJDAEC061204/" target="_blank">unihemispheric slow-wave sleep</a>, and dolphins do it, too. A dolphin will shut down one hemisphere of its brain, leaving the other half of the brain to monitor breathing functions and keeping that eye open to monitor its environment. The left eye will be closed when the right half of the brain sleeps, and vice versa.We humans can actually do this, as well -- kind of. Sleep researchers have documented unihemispheric slow-wave sleep in people, though it's not a full hemispheric separation. It's more of an asymmetry and it's associated with the <a href="http://www.cell.com/current-biology/abstract/S0960-9822%2816%2930174-9" target="_blank">first night effect</a>, in which people have trouble getting a good night's sleep in a new location. One hemisphere of the brain remains more active and vigilant, monitoring the environment for unfamiliar sounds in the new surroundings.So that old expression about sleeping with one eye open? It's actually pretty accurate. Double Secret Bonus Fact: Because of their tendency to steal food from other seabirds, frigatebirds are classified as <a href="http://www.reed.edu/biology/courses/BIO342/2012_syllabus/2012_WEBSITES/Erin_A_and_Ryan_S%2011-20final/index.html" target="_blank">kleptoparasites</a>.-- <a href="http://www.seeker.com/community/glenn_mcdonald" target="_blank">Glenn McDonald</a>Learn More:NPR: <a href="http://www.npr.org/sections/thetwo-way/2016/06/30/484164544/non-stop-flight-how-the-frigatebird-can-soar-for-months-without-stopping" target="_blank">Nonstop Flight: How The Frigatebird Can Soar For Weeks Without Stopping</a>Science Alert: <a href="http://www.sciencealert.com/scientists-have-just-seen-birds-sleep-while-flying-for-the-first-time-ever" target="_blank">Scientists have just seen birds sleep during flight for the first time ever</a>Nature: <a href="http://www.nature.com/ncomms/2016/160803/ncomms12468/full/ncomms12468.html#methods" target="_blank">Evidence that birds sleep in mid-flight</a>

How Can Birds Sleep While They're Flying?

Animals

Earth & Conservation

The Number of Bird Species Could Be Double What We Thought

There could be twice as many bird species as we thought.

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