Hold your arms out with your palm oriented vertically, as if you were trying to shake someone’s hand. Now without moving your forearm, bend your hand downwards towards the floor. Unless you are freakishly flexible, you will only have managed to a measly acute angle. But if you were a bird, you could bend your wrist so that your hand pointed back towards your body. These incredibly flexible wrists allow birds to fold their wings and they help with flying. And many dinosaurs could do something similar.
Many older depictions of small raptors, including the Jurassic Park films, have them holding their arms in a zombie-like stance – arms out at the front and hands palms-down. More recently, artists have portrayed them with more bird-like postures, with their hands bent back towards the forearm. How far the hand could actually bend has been an open question, so Corwin Sullivan from the Chinese Academy of Sciences decided to answer it by piecing together the evolution of the raptor wrist together with Dave Hone (who blogs at Archosaur Musings), Xing Xu and Fucheng Zhang,
Sullivan examined the hands of several dinosaurs, from large hunters like Allosaurus, to smaller, more bird-like species like Caudipteryx and Deinonychus, to living examples like the turkey. He showed that the asymmetric wrists first appeared in this dynasty of predators. They gradually became increasingly asymmetric and backward-bending, culminating in the flexible versions of early birds. This is particularly a tale of two wrist bones – the radiale, which became increasingly wedge-like, and the semilunate carpal, which developed a rounded, convex dip.
These changes to the raptor wrist were already well underway before the group developed powered flight and possibly even before the evolution of long feathers on the arms. For the moment, it’s not clear what advantage the dinosaurs would have gained from their slightly more flexible wrists.
Cities are noisy places. If you ever get annoyed by the constant din of traffic, machinery and increasingly belligerent inhabitants, think about what songbirds must think. Many birds rely on songs to demarcate their territories and make their advances known to mates. They listen out not just for the sounds of seduction or rivalry, but for approaching predators and alarm calls that signify danger. Hearing these vital notes may be the different between life and death.
Last year, I wrote a feature for New Scientist about the effect that urban noise has on songbirds. Those that can’t make themselves heard are being pushed out of cities; others have developed strategies to rise above the clamour. British robins have avoided the traditional dawn chorus, when rush hour is at its peak, in favour of night-time singing when their tunes can stand out. German nightingales take the more straightforward approach of singing very loudly, belting out their songs at 95 decibels, enough to damage human hearing if sustained. And some species – great tits, house finches and blackbirds – have opted for higher notes, which are less easily masked by the typically low frequencies of urban noise.
So some species are adaptable enough to thrive in a cacophonous environment that would drive out those that can’t change their tune. And if the species that are driven away include predators and thieves, the birds that remain fare even better. That scenario is playing out in the cities of America. Clinton Francis from the University of Colorado at Boulder has found that noise reduces the diversity of bird communities but it actually helps those that remain.
Previous studies have linked the presence of noisy roads and industries with sparser populations of local birds, but never conclusively. Noise is also associated with habitat changes or visual disturbances, and it makes it harder for scientists themselves to spot birds – all of these factors could explain any disappearances.
To get around these problems, Francis relied on a unique natural experiment, taking place in the woodlands of New Mexico. Here, natural gas is pumped out of the ground and at some sites, it is then pushed along pipelines by compressors that are very noisy and that operate constantly. Other sites that lack compressors are much quieter but essentially the same in terms of environment and the surrounding trees. By comparing woods near noisy and quieter gas wells, Francis could isolate the effects of noise from those of the mere presence of industry. He even managed to get the compressors turned off for short windows while his team took stock of the local birdlife.
There 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?
Like almost all birds, a chicken’s genome – its full complement of DNA – is remarkably small. DNA is made up of millions of units called ‘base pairs’, just like a book contains millions of letters. A typical bird genome is made up of about 1.5 billion of these base pairs, just half the number of the comparatively flabby human genome. Like their bodies, bird genomes are feather-weight and streamlined.
Some scientists have suggested that, over the course of evolution, birds shrunk their genetic packages to help them fly. Smaller genomes involve less DNA, which in turn can be housed in smaller cells. And smaller cells are more energy-efficient than larger ones, in the same way that a Mini is more efficient than a gas-guzzling SUV.
For many animals, living with others has obvious benefits. Social animals can hunt in packs, gain safety in numbers or even learn from each other. In some cases, they can even solve problems more quickly as a group than as individuals. That’s even true for the humble house sparrow – Andras Liker and Veronika Bokony from the University of Pannonia, Hungary, found that groups of 6 sparrows are much faster at opening a tricky bird feeder than pairs of birds.
After ruling out several possible explanations, the duo put the speedy work of the bigger flock down to their greater odds of including boffin birds. Individual sparrows vary greatly in terms of their skills, experiences and personalities. Larger groups are more likely to include the sharpest bird brains, or several diverse individuals whose abilities complement each other.
Wild animals constantly encounter new, unfamiliar and challenging situations and the ability to adapt to them more quickly may give social species an edge over loners. The problem-solving advantages of groups have been demonstrated in humans. Three people, far from being a crowd, solve intellectual tasks faster than pairs or individuals, even if they were the smartest of the sample. There has been much less research on other animals, although scientists have certainly found that large groups of birds or fishes find food faster and more efficiently than smaller groups.
But Liker and Bokony’s sparrow experiments are the first to show that large animal groups outperform smaller ones at problem-solving tasks where they have to invent new techniques. House sparrows are a good choice for a study like this. They are very social birds that live in flocks of anywhere from a few individuals to a few hundred. They are opportunists that use their relatively large brains to find food in all sorts of new environments.
In the summer of 2007, thirty-four travellers left home with backpacks in tow to see the world. But these weren’t human students, out to
get drunk and pretentious find themselves in foreign lands – they were small songbirds, migrating to tropical climates for the winter.
Their backpacks were light-measuring devices called “geolocators”, each about the size of a small coin. By measuring rising and falling light levels, these miniature contraptions revealed the timings of sunrise and sunset wherever the birds happened to be flying. Those, in turn, revealed where they were in the world, and allowed Bridget Stutchbury from York University, Toronto to achieve a world-first – track the entire voyage of a migrating songbird, from the start of the outbound trip to the end of the return journey.
The recordings show that tiny wood thrushes and purple martins are far more capable fliers than anyone had thought. They can cover 500 kilometres in a day, flying more than three times as fast as previously expected. Previous studies had credited these tiny fliers with top migration speeds of just 150 km/day. But these had major flaws.
Songbirds are so small that they can’t be tracked by satellites, making their annual migrations difficult to track. Until now, what we knew about their journeys came from brief glimpses on radar or studies done at pit-stops along the way. One incredible study managed to track thrushes during a short part of their travels by injecting them with mildly radioactive isotopes and following them in a plane. All of these studies have provided mere glimpses of the overall migration, like piecing together a movie from still shots and trailer clips. Stutchbury’s team from the University of York, Toronto have managed to record the entire film.