Swallows may be evolving to dodge traffic‏

Roadside-nesting cliff swallows have evolved shorter, more manoeuvrable wings, which may have helped them to make hasty retreats from oncoming vehicles, according to a study published in Current Biology1.

The study’s authors discovered the trend after noticing that the number of vehicle-killed birds had declined over the past three decades. They suggest that the two findings provide evidence of roadway-related adaptation.

“I’m not saying that it’s all because of wing length,” says Charles Brown, a biologist at the University of Tulsa in Oklahoma and one of the authors of the study. But, he says, the shortening does support the idea that the birds are adapting to disturbed environments, as other organisms presumably are.

Together with Mary Bomberger Brown, a ornithologist at the University of Nebraska–Lincoln, Brown tracked roadside populations of cliff swallows (Petrochelidon pyrrhonota) in western Nebraska for 30 years, mostly to study the birds social behaviors within their colonies.

These birds winter in South America but breed in North America, in colonies of up to 12,000 adults. They typically build their conical, mud-based nests into the sides of cliffs, but have also taken to living under bridges and highway overpasses.

As the two researchers checked the roadside colonies, Brown, an amateur taxidermist, collected dead swallows for skinning and stuffing — gathering 104 vehicle-killed adults and 134 adults killed accidentally in nets used for the study. When he and Bomberger Brown noticed a decline in the annual number of roadkills — even though the overall population was increasing — they compared the wing measurements of both types of stuffed bird.

The team discovered that vehicle-killed birds had longer wings than birds that died in nets, and that while the wings of the vehicle-killed birds had lengthened over time, those of net-killed birds — which represented the general population — had shortened.

Escape strategy

Brown says that there is evidence that shorter wings make the animals more agile: “they can make a 90º turn more rapidly”, he says. That would help the birds to dodge traffic as they exit or enter their nesting sites, or take off from the pavement, Brown explains. And that in turn would enable them to survive and produce more short-winged offspring.

The researchers tried to rule out other factors that might have explained the decline in roadkill — including changes in methods to find the animals, traffic patterns, predators, diseases and scavengers — but acknowledge that it might have been caused by behavioural changes, such as the birds learning to avoid cars.

Taxidermist Johannes Erritzoe at the House of Birdresearch in Christiansfeld, Denmark, has also noticed a decline in the number vehicle-killed birds around Denmark, and suspects natural selection. Although he has not yet measured wing length, he says that he now plans to do so.

It is hard to definitely prove that animals are adapting to living around roads, says behavioural ecologist Colleen St. Clair at the University of Alberta in Edmonton, Canada. But, she says “this is the best demonstration that they do have that capacity”.
Source

All it is, is learned behavior. It has nothing to do with genetic evolution or anything as ridiculous as that.

The leaping sharks of South Africa have not evolved, they are displaying learned behavior, same with the dolphins of Florida who teach their young to do the same thing, and always on their right side, and the whales of British Columbia etc etc etc.

All, it is is learned behavior, the same way children don't get killed on the road when they learn to look left right and left before crossing (or the other way around).

reply to post by pacifier2012


The legnth of the wing-span of a bird is not something that is a learned behavior. It's a physical trait. Much the same as I can't "learn" to have shorter arms. While I don't think there's enough evidence to prove that the wing-span of these birds is evolving and changing for the reason of cars in my opinion, that doesn't mean that it can't be.

Thanks for the post OP. I love these types of finds.