No one is completely sure what whale songs are used for – theories include mating calls, other forms of communication, and possibly a form of sonar. A group of researchers recently examined whale songs from several decades and from all the world's oceans. They found that the frequency, or pitch, of blue whale song has been steadily dropping for many years. Recently recorded whale songs are the lowest, while whale songs from the 1960s were higher in pitch.

The researchers don't know what's causing the change, but they have a theory based on a correlation with blue whale populations. When the songs were at their highest pitch, blue whales had been hunted to the brink of extinction. Since the International Whaling Commission banned blue whale hunting in the 60s, the worldwide blue whale population has been slowly but steadily increasing (though it's still a tiny fraction of what it once was). That seems to coincide with the pitch change.

It could be that whales used a higher frequency song when there were fewer whales because those songs traveled farther, hundreds of miles or more. With a sparse population, you'd need a long-distance call to find more mates or family members. With populations rebounding somewhat, the whales are able to use lower frequency songs with more success, since there's a greater chance another blue whale is nearby.

You may be wondering why higher frequency songs would travel farther, since generally low-frequency sounds are thought to be better for long-distance propagation. I asked the researchers about this, and scientist Mark McDonald explained that whales can sing louder at higher frequencies:

Across the frequencies of blue whale song, the underwater transmission losses are nearly the same regardless of frequency. It is absorption which is the primary cause of frequency dependent transmission losses, rather than dispersion in this case, and the absorption loss only begins to become significant when ranges reach thousands of kilometers. Theory tells us the whales can produce higher amplitude songs at higher frequencies, based on given lung volume.

I was also curious if this was an example of evolution in action, with subsequent generations of whales exhibiting a change in pitch due to natural selection, or if it was a behavioral change, with blue whales choosing to use a lower pitch song. He replied:

We presume it is a behavioral change, but we don't really know why the whales are changing their song frequency. We don't find our own best hypothesis entirely convincing.

Which is a pretty excellent example of science in progress. If only we could figure out what blue whales were singing about, so we could just ask them.

The pitch of blue whale songs is declining around the world, scientists discover [via EurekAlert!]

Photo: NOAA.

Normally relocating bears is frowned on as a way of saving populations. Conventional environmental science says that a declining population should not be moved until the sources of its decline have been addressed. But this group of French biologists say that in this case, they have population models that prove the cause of the decline in the population has to do with a gender disparity.

While you might think this solution is obvious, it isn't. You see, the problem with these bears isn't that there aren't enough females to breed a new population - in fact, there are. Instead, the problem comes from the bears' practice of co-rearing their young, with the fathers sticking around to care for their offspring. Because the babies take a while to mature, there will be long stretches where some males are fathers and others aren't. The single bears will fight the fathers. When single bears win, they murder the father's offspring so they can parent their own children. As a result, even a slight gender imbalance between the bears can result in viable offspring being killed over and over.

The scientists' study was published yesterday in PLoS One. A release about the study explains:

The researchers analyzed field data collected from 1993 to 2005 and found that the western sub-population had much lower reproductive success than the central sub-population. They suggest this could be the consequence of the western sub-population being inbred or having a male-biased sex ratio. In species with extended parental care, a male-biased sex ratio can induce sexually selected infanticide, a behavior in which males attempt to kill unrelated cubs to induce estrous in females, maximizing their opportunity to breed.

[Researcher Guillaume] Chapron and his colleagues used a population model to compute how many bears should be released to ensure viability, and showed the population could recover provided an adequate number of new females are translocated.

via PLoS One

Researchers reported this week in Proceedings of the National Academy of Sciences that they found have found shock-synthesized diamonds — known to result from impact events — in the Arlington Canyon on Santa Rosa Island in California, and have previously found similar diamonds in the Greenland Ice Sheet. The placement of the Arlington Canyon diamonds coincide with North America's oldest known human remains — from the Clovis people, who went extinct nearly 13,000 years ago — and the disappearance of the pygmy mammoth from Santa Rosa. This fits with the team's earlier speculation that a comet strike led to a mass mammalian extinction across North America:

In 2007 researchers theorized that a comet set off continental fires that led to the mysterious disappearance of the Clovis people and the extermination of 35 mammal genera, including mammoths, mastodons, ground sloths and camels. The team documented a "black mat" of charcoal throughout North America that contains high levels of iridium, magnetic spheres, and nano-diamonds, which are consistent with such an airburst.

However, the hypothesis remains controversial, and other geologists and archeologists are reluctant to buy the diamonds as evidence of a comet-induced die-off, especially given the absence of an impact crater.

Did a Comet Cause a North American Die-Off around 13,000 Years Ago? [Scientific American]

A team from UC Santa Barbara is working on this very question, and they've just published a study in the Proceedings of the National Academy of Sciences. They believe Earth is in its sixth mass extinction, which will kill off nearly 50% of all plant and animal species. Figuring out which endangered plants to save may be the key to minimizing the ecological impact of this particular extinction:

"Losing a very unique species may be worse than losing one with a close relative in the community," said [co-author Todd] Oakley. "The more evolutionary history that is represented in a plant community, the more productive it is."

[Post-doctoral fellow Marc W.] Cadotte explained that the buttercup is a very unique species, evolutionarily. Losing the buttercup, where it occurs in grasslands, would have a much bigger impact on the system than losing a daisy or a sunflower, for example. The latter species are closely related. Each could therefore help fill the niche of the other, if one were to be lost. The daisy and sunflower also have a more similar genetic make-up.

It may be a sad day for the daisy, but ensuring the survival of a genetically diverse array of plant life will help ensure a sufficient level of biomass, and could reduce the devastation a mass extinction would cause.

Image by Martin Heigan.

Current Mass Extinction Spurs Major Study of Which Plants to Save [via Science Blog]

Although the tortoises vanished from the Floreana, a handful were preserved by the very sailors who contributed to their extinction. When they didn't need the tortoises for food, the sailors would drop the tortoises off at their whaling grounds, notably the Galapagos island of Isabela. There the Floreana tortoises interbred with the native tortoises, allowing their DNA to live on:

"The [living tortoise] samples were collected in 1994, but we had no idea what was in there because we didn't have Floreana data," said Gisella Caccone, an evolutionary biologist at Yale University in New Haven, Conn. "OK, now we have genotypes for 15 to 25 animals from the museums, so we did the analysis and boom!"

Sadly, the biologists won't be staging any Jurassic Park-style cloning to revive the reptile, as is being planned for a baby mammoth fossil discovered in Siberia last year. Instead, they will determine if there are enough tortoises carrying the Floreana DNA to begin a selective breeding program.

Extinct Giant Tortoise Could Be Revived [LiveScience]

NASA's list of potentially hazardous asteroids (PHAs) currently numbers 959. That's 1,000 asteroids that astronomers pretty much know are going to get closer than 7.5 million kilomters to Earth, about 20 times the distance from here to the Moon. Five of those are expected to come between Earth and the Moon over the next century.

So we'll have a few close shaves but nothing to worry about, right? Not so fast. The total number of PHAs and comets astronomers think are out there is probably more like 20,000. That means we've mapped about 5% of the objects that stand a good chance of hitting us. So take the future part of this chart as a best-case scenario. The past five close encounters, however, show just how vulnerable we are:

1) The Comet of 1491. This one must've scared the hell out of some folks. At a little less than four times the distance to the moon, this was the closest pass ever recorded at the time, and no one knows for sure how big it was. Little did our ancestors know how much more interesting things would get.

2) Tunguska, 1908. One of the most famous Earth lcose calls of all time, it was also a pipsqueak. For a long time scientists believed a comet perhaps 60 meters in diameter exploded over Siberia with a force of as much at 30 megatons, or about 2,000 times more powerful than the atomic bomb dropped on Hiroshima, though nothing solid ever hit the planet. All those pictures of flattened forest certianly look impressive, but last year, scientists re-crunched the numbers and found that the comet oculd've been as small as 30 meters, and the blast just 5 megatons. In other words, much smaller objects can do way more damage than we ever thought before. Gulp.

3) The Great Daylight Fireball of 1972. The name says it all — it doesn't get much closer than this. Size estimates range from 3 to 14 meters in diameter, depending on whether it was ice or rock. Whatever it was, the object called US19720810 burned through the atmosphere from Utah to Canda for about a minute and a half. Luckily, the space rock struck a glancing blow — had it hit Earth directly, it could've blasted us with 1/2 a Hiroshima worth of energy.

4) 2004 FH and 2004 FU162. At 30 meters in diameter and made of solid rock, 2004 FH would be a thumper of Tunguska proportions if it ever hit home. In the right (or wrong) place, it could detroy a city. As it was, it passed 43,000 kilometers above Earth on on March 18, 2004.

Three weeks later, FU 162 came whizzing along. Astronomers basically discovered it at bascially the same time as the 6-meter in diameter rock soared just 6,400 kilometers above Earth's surface.

5) Comet Hyakutake. Now we're getting into civilization-threatening territory. At 2 kilometers in diameters, this comet only got within about 40 lunar distances to Earth in 1996. Compared ot our other close calls, that's pretty comfortable, but considr this: it was discovered less than two months before its closest pass. Had it been on a collision course with Earth there's almost nothing we could've done other than brace for the millions dead, massive climate disruption, crop failure, 500-foot high tsunami...you get the idea.

FUTURE:

6) 1999 AN10. In a little less than 20 years, our usually quiet Earth-Moon system is going to have a lot of visitors. In August 2027, AN 10 is going to get about one lunar distance from Earth, and we'll get a chance to see just how big this bad boy is. Estimates range from 1/2 to 2 kilometers in diameter, plenty large to leave a dent in humanity if it ever gets closer.

7) 2001 WN5. Just six months after AN10 comes a callin' WN5 will get even closer, just about splitting the difference between Earth and the Moon. At 700 meters in diamters, this asteroid has a got potential for major dmaage, but current odds of impact are rated a negligible.

8) 99942 Apophis. By far the most famous of the end-bringing objects we know about in our solar system, astronomers thought for a while that this 270 meter-wide rock had an almost 3% chance of hitting us. Since then, odds have been lowered to 1 in 43,000 that it could slam into Earth in 2029. But if it passes through a gravitaitonal keyhole — a tiny region in space that could tweak its orbit ever so slightly — an impact could still happen on April 13, 2036.

9) 2005 WY55. Just 200 meters wide, astronomers think this asteroid could still pack a wallop. Right now it's scheduled to get within about 75,000 km of Earth, but impact odds are big enough to kep in mind — currently they're rated at around 1 in 70,000. If our number comes up on that faeful dayin May 2065, look out — blast yield estimates from this rock range to 1100 megatons.

10) 2000 WO107. Depending on how well humanity holds up under climate change, bird flu, and all the other things that could potentially kill us off, we might be able to look up and see WO107 zoom by in December 2140. The 400 meter-wide rock isn't scheduled to hit us — it should get about half way between Earth and the Moon — but if calculations are off by even a little bit (and all of the future examples here have some uncertainty) we could care a lot.

Sources: NASA's Near Earth Object Program, Harvard List of PHAs

Additional research by Nivair H. Gabriel. Image by Stephanie Fox.

Crunchy goodness: 5

Spinoffs/Sequels/Copycats: A movie adaptation is in the works, reportedly featuring the Disburbia team of Carl Ellsworth, DJ Caruso, and (sadly) Shia LaBouf.

Elevator pitch: What if women ran the world, and turned out to be just as big assholes as the men?

Deadliest spoiler: Yorick isn't really the only man left. Oh, and the awesome Agent 355 dies after Yorick confesses his love for her.

Strange Horizons Review by Jed Hartman