Songbirds need so-called “human language gene” to learn new tunes

Blogging on Peer-Reviewed ResearchThe nasal screech of Chris Tucker sound worlds apart from the song of a nightingale but both human speech and birdsong actually have a lot in common. Both infants and chicks learn their respective tongues by imitating others. They pick up new material most easily during specific periods of time as they grow up, they need practice to improve and they pick up local dialects. And as infants unite words to form sentences, so do songbirds learn to combine separate riffs into a full song. Songbirds need so-called “human language gene” to learn new tunes

Because of these similarities, songbirds make a good model for inquisitive neuroscientists looking to understand the intricacies of human speech. Zebra finches are a particularly enlightening species and they have just shown Sebastian Haesler that the so-called human ‘language gene’ FOXP2 also controls an songbird’s ability to pick up new material.

FOXP2 has a long and sordid history of fascinating science and shoddy science writing. It has been consistently mislabelled as “the language gene” and after the discovery that the human and chimp versions differed by just two small changes, it was also held responsible for the evolution of human language. Even though these claims are far-fetched (for reasons I’ll delve into later), there is no doubt that faults in FOXP2 can spell disaster for a person’s ability to speak.

Mutated versions cause a speech impairment called developmental verbal dyspraxia (DVD), where people are unable to coordinate the positions of their jaws, lips, tongues and faces, even though their minds and relevant muscles are in reasonable working order. They’re like an orchestra that plays a cacophony despite having a decent conductor and tuned instruments.

Brain scans of people with DVD have revealed abnormalities in the basal ganglia, an group of neurons at the heart of the brain with several connections to other areas. Normal people show strong activation of FOXP2 here and fascinatingly, so do songbirds. Haesler reasoned that studying the role of this gene in birds could tell him more about its human counterpart.

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Evidence that Velociraptor had feathers

In Jurassic Park, the role of Velociraptor was played by computer-generated reptilian actors, that bore little resemblance to the real deal. The actual dinosaur was smaller, slower and used its infamous claw to stab rather than disembowel. And now, scientists have found conclusive proof that it was covered in feathers.

Since Jurassic Park aired, dinosaurs like Velociraptor have received something of a makeover. It began in the late 1990s when Chinese palaeontologists found a stunning series of dinosaur fossils with distinct traces of feathers around their bodies. Some were just covered in a downy fluff, while others like Microraptor had fully-formed wings and were probably capable of true flight.

Quill knobs on the forearm of a VelociraptorThese species were primitive members of the dromaeosaurids, a group of small, agile predators that Velociraptor also belongs to. With feathered ancestors and evolutionary cousins, it was always extremely likely that Velociraptor also had a feathered coat but until now, that was always an educated guess.

Quill knobs

The breakthrough came from Alan Turner and Mark Norell from the American Museum of Natural History and Peter Makovicky of the Field Museum of Chicago. They were studying the forearm of a Velociraptor unearthed in 1998, when they noticed six evenly spaced knobs of bone on the back edge.

The team recognised these as quill knobs, small lumps of bone that act as attachment points for feathers. These knobs are direct evidence that Velociraptor carried a row of feathers on its forearm, probably about 14 by Turner’s count. You can see them in the top two images above. The bottom two show the equivalent structures in a modern vulture, and how feathers are attached to them.

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Clever New Caledonian crows use one tool to acquire another

You don’t have to be particularly intelligent to use tools – many animals do so, including some insects. But it takes a uniquely intelligent animal to be able to combine different tools to solve a problem. We can do it, the great apes can do it, and now the New Caledonian crow joins our exclusive club.

New Caledonian crows are very advanced tool users.Animals can use tools using little more than pre-programmed behaviour patterns that require little intelligence. But combining tools, or using one tool on another (a metatool, if you will), is a different matter entirely – that takes reasoning.

This type of intelligence has been the engine of human innovation. It allowed us to use simple tools to make advanced ones, or to combine different tools into increasingly complex machines.

The majority of animals lack the ability to manipulate tools in this way and in primates, the line is drawn at the great apes – they can (mostly) do it, but monkeys struggle. So it may come as a surprise that a humble bird has now been found to use metatools to the same standard as our ape cousins – the New Caledonian crow.

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Dinosaurs provide clues about the shrunken genomes of birds

I’m baaaack! So, newly married and after two weeks of honeymooning, I return to my regular blogging schedule, refreshed and relaxed.

Today is also an auspicious day – it’s been a year since I first started this blog and it’s completely exceeded all my expectations (in that some people are reading it, which is more than my predicted no people).

So, without further ado, the science. I haven’t had time to pen a new article, but here’s a slightly old one.

 

 

Tyrannosaurus had a genome half the size of a house mouseThere is a reason why there are no dinosaur geneticists – their careers would quickly become as extinct as the ‘terrible lizards’ themselves. Bones may fossilise, but soft tissues and molecules like DNA do not. Outside of the fictional world of Jurassic Park, dinosaurs have left no genetic traces for eager scientists to study.

Nonetheless, that is exactly what Chris Organ and Scott Edwards from Harvard University have managed to do. And it all started with a simple riddle: which came first, the chicken or the genome?

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Argentavis, the largest flying bird, was a master glider

The largest ever flying bird, Argentavis, was a giant predator, as big as a light aircraft. But how did such a giant take to the skies and stay there?

An artist rendering of ArgentavisSix million years ago, the skies of Argentina were home to fearsome predator – Argentavis magnificens, the largest bird to ever take to the air. It weighed in at 70kg and had a wingspan of 7m, about the same size as a Cessna 152 light aircraft.

Argentavis was a member of an extinct group of predatory birds understandably called the teratorns – ‘monster birds’. They are related to storks and New World vultures such as turkey vultures and condors. But Argentavis completely dwarfed even the massive Andean condor, weighing six times more and with a wingspan over twice as long (in the picture below, its silhouette is placed next to a bald eagle for scale).

There is no question that Argentavis flew. It has all the characteristics of modern flyers including light, hollow bones and strong, sturdy wings. It’s how it flew that palaeontologists have puzzled over, given its massive size in relation to modern birds.

Take-off

For a start, how did it get its large bulk off the ground in the first place? The heaviest living flier, the Great Kori Bustard, is over three times lighter than Argentavis, and even it can only take off after arduously ‘taxiing’ like a airplane.

Sankar Chatterjee from the Museum of Texas Tech University decided to model the giant’s flying style by running simulations with known fossils. He found that Argentavis simply couldn’t have generated enough lift from a running-take-off.

It needed height to get airborne, but it could manage with surprisingly little. Even a gentle down-slope of 10° and a light headwind would have given it enough extra power to avoid an embarrassing crash. Albatrosses and hang-glider pilots use the same technique today.

In the air

Argentavis’s formidable skeleton, in comparison to a bald eagle.Once in the air, the flapping flight that small birds use was out of the question for the giant predator. By studying its skeleton, Chatterjee estimated the maximum amount of power that its flight muscles could have generated. And while substantial, it was still 3.5 times less than the minimum amount of power needed to fly.

Instead, Chatterjee believes that Argentavis was a master glider. It was capable of soaring for great distances at a shallow angle of 3°, continually re-shaping its wings to control its glide.

Unlike flapping, the efficiency of gliding doesn’t change very much with size, if a bird sticks to the standard body plan. So despite its enormity, Argentavis sailed through the air with as much grace as much smaller species like the buzzard or white stork.

Like modern soarers, Chatterjee believes that Argentavis used two techniques. By flying along the Andean ridges, it stayed aloft using upwards air currents produced by wind deflected up the cliffs. The several fossils found at the Andean foothills support his idea.

Because of its efficient gliding, it could stay aloft using relatively slow drafts of wind. Chatterjee calculated its top speed at about 70 km/h, allowing it scan vast tracts of land for prey. It’s a very energy-efficient style and today, eagles and vultures use it to great effect, sometimes covering hundreds of miles without a single wing flap.

Hot air

When the bird switched from the mountains to the wide, open spaces of the pampas, it switched to a different method – thermal soaring, where rising columns of hot air provided it with lift.

Thermals are hot rising columns of air.Popcorn-like cumulus clouds betray the location of thermals, and by circling around one, Argentavis could have risen through the air, giving itself enough height to soar to the next thermal. Despite its large size, Chatterjee calculated that Argentavis was manoeuvrable enough to manage the tight circular turns needed to stay within a thermal column.

Even with this reliance of thermals, Argentavis was pushing the limits of even gliding flight. Any heavier and it would have exceeded the maximum weight for safe gliding. So why are there no equally sized giants today?

Chatterjee thinks that the late Miocene’s climate provided the answer. Six million years ago, Argentina was much hotter and drier than it is today – just the weather needed for generating the powerful thermals needed to lift such a large bird.

Argentavis was beautifully adapted to take advantage of this large, open habitat, where it could travel across large distances in search of prey. And unlike modern condors, it was no mere scavengers. Its skull was as long as my forearm and ended in a formidable hooked beak – it was an active hunter, possibly taking prey on the wing. .

Reference: Chatterjee, Templin & Campbell. The aerodynamics of Argentavis, the world’s largest flying bird from the Miocene of Argentina. PNAS doi.10.1073/pnas.0702040104.

Images from PNAS paper and Apokryltaros

Related posts on extinct animals:
Bone-crushing super-wolf went extinct during last Ice Age
Microraptor – the dinosaur that flew like a biplane
How many types of dinosaur were there?
Tracks provide evidence of swimming dinosaurs

Attack of the killer mice – introduced rodents eat seabird chicks alive

On Gough island, introduced mice have developed a grisly appetite for seabird chicks and could well drive local species to extinction.

As Charles Darwin learned several centuries ago, islands are havens for evolution. Newcomers to these isolated worlds find themselves unshackled from the predators that dogged them on the mainland. They celebrate their freedom by diversifying into a great variety of species.

A Gough Island mice sites amid a grisly pile of chick bodies.But predators still have ways of tracking them down, and following the footsteps of sailors is one of them. By killing adults and eating eggs, introduced predators such as rats, cats and stoats are responsible for nine in ten of the bird extinctions since 1600.

Now, conservation agencies are getting serious about introduced predators. As an example, they have spent increasingly large budgets in recent years on the eradication of rats from troubled islands.

Smaller stowaways like mice typically escape the conservationists’ wrath, and between 2001 and 2005, twenty-five times less money was spent on dealing with them. After all, mice are smaller and less opportunistic than rats and pose very little threat to seabirds.

Or at least that was what scientists used to think. In 2005, Ross Wanless, Peter Ryan and colleagues from the University of Cape Town found that on Gough Island in the south Atlantic, mice had developed sinister appetites. They were eating the chicks of local seabirds alive (see image below).

Infrared footage shows mice feeding on a chick.

House mice were introduced to Gough Island, now a World Heritage Site, in 1888 and are the only introduced mammals there. They share the island with large seabird colonies including many endangered species, and the last breeding populations of the Tristan albatross and the Atlantic petrel.

The mice seemed to be co-existing peacefully until the turn of the millennium, when some of the seabirds started experiencing massive breeding losses.

Wanless investigated and by watching about 300 nests, he found video evidence that the mice have developed a taste for albatross, petrel and shearwater chicks. They were attacking and eating chicks up to 300 times their weight, and often en masse.

Albatross chicks are not defenceless and will often ward off much larger avian hunters like the sub-Antarctic skua or the southern giant petrel. But they have also been spoilt through an evolutionary history free of mammalian dangers. The chicks have no idea how to react to mice, let alone defend themselves, hapless and helpless.

To save endangered birds like the albatross, ALL introduced predators must be dealt with.In fact, Wanless describes the mice as parasites rather than predators. They often don’t kill the chicks outright but slowly feed from open wounds over the course of days.

Typically, 60-75% of Tristan albatross young survive their first year. But thanks to the voracious mice, only 27% now do so on Gough Island. As a result, the population of this already vulnerable bird has crashed by over a quarter since the 1960s.

The birds of Gough Island will clearly need some assistance. Meanwhile, Wanless is sounding the alarm for other islands where introduced mice roam free.

On islands where they are not alone, larger introduced predators like cats or rats may be helping to keep their numbers down. The danger then, is that when conservationists get rid of these larger problems, they may unwittingly unleash a smaller foe on the native animals.

This very situation seems to be playing out on Marion Island in the South Indian ocean. In the 1990s introduced cats were finally eradicated from the island, leaving mice as the only mammal aliens around.

And sure enough, Ryan has found that several wandering albatross chicks have died of wounds consistent with mouse attacks. These attacks could be much more widespread than we had realised.

The message is clear – eradication programmes for introduced animals should target all potential predators, whether big or small. As in the case of sharks and scallops dealt with elsewhere in this blog, the removal of top predators can often doom animals at the bottom of the food chain by releasing hunters in the middle tier.

Reference: Wanless, Angel, Cuthbert, Hilton & Ryan. 2007. Can predation by invasive mice drive seabird extinctions? Biology Letters doi:10.1098/rsbl.2007.0120

Eavesdropping songbirds get predator intel from overheard calls

Animals gain valuable information on incoming predators by listening to the alarm calls of the communication of other species. New experiments with chickadees suggest that both alarm calls and the understanding of them are more complex than we had thought.

Humans are a funny lot. While we seem to be relentless voyeurs, we generally frown on eavesdropping as an invasion of privacy. But in the animal world, eavesdropping can be a matter of life or death.

The black-capped chickadee encodes information on predator size in its call.Animals rarely communicate in isolation. Often it pays for one species to monitor the dialogues of others, particularly when predator warnings are involved. Small animals in particular do well to pay attention to the alarms of other species, as they are often preyed upon by the same larger hunters.

Even very unrelated species can listen in and understand each other’s signals. Vervet monkeys respond to the alarm calls of superb starlings, while mongooses are well-versed in hornbill calls.

Alarm calls aren’t just a simple matter of shouting “Look out!”, and many species have different calls for different predators. But one of the most sophisticated alarm systems so far discovered is used by a small, unassuming bird called the black-capped chickadee

The chickadee acts as an inadvertent sentry for a multitude of bird species. Its name comes from its distinctive “chick-a-dee” alarm call, made in response to a perched bird of prey or a land predator.

The black-capped chickadee has one of the most complex alarm calls so far discovered.When this call sounds out, anywhere between 24 and 50 species of bird marshall together and mob the predator, robbing it of the element of surprise and harassing it from the area.

The chick-a-dee call is not a blunt warning, but a sophisticated piece of communication. By varying the acoustics of the call, the chickadee can warn others about not only the type of predator, but also its potential threat and size.

Smaller raptors, with their superior maneuverability, pose a greater danger to small birds and must be dealt with more carefully. When these hunters are near, the birds warn of their presence by shortening the gap between chick and dee, and add extra dees to the end.

Now, Christopher Templeton and Erick Greene from the University of Washington have found that other birds have learned to appreciate the subtle differences in the chickadee’s calls.

The red-breasted nuthatch has learned to understand the subtle variations in chickadee alarm calls.They recorded two variants of the chick-a-dee call, by exposing the birds to two species of owl, one large and one small, in controlled encounters. They then played the calls back to red-breasted nuthatches – common flock-mates of chickadees – from a speaker hidden in a tree. As predicted, the nuthatches mobbed the speaker in response to both calls.

But on closer inspection, they were clearly picking up on the greater threat suggested by the subtly different small-predator call. When that was played, they mobbed more frequently and for longer, approached the speaker more than twice as closely, showed more wing-flick displays (a sign of agitation), and were themselves more likely to call.

Conserving their energies for only the most dangerous predators could bring great benefits to the nuthatches, especially in winter, when they are most likely to be found in the company of chickadees. Their food sources are scarce, and keeping warm saps valuable energy. Understanding the subtle differences in the chickadee dialect could help them save their energy for the times of greatest need.

Templeton and Greene’s study shows that animals can pick up a surprisingly complex picture of their environment by listening in on other conversations.

 

Reference: Templeton & Greene. 2007. Nuthatches eavesdrop on variations in heterotrophic chickadee mobbing alarm calls. PNAS 104: 5479-5482.

Image: Nuthatch photo by Alan D Wilson.

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