Wings of swallows shrink to avoid death by vehicles, study shows

By Tiago Zenero, NewsNetNebraska

Thirty years ago, Mary Brown, started to research birds in Nebraska with a seemingly simple question: why do animals live in groups?

“We chose cliff swallows because we knew they are the most sociable, but they live in groups of different sizes. Some live by themselves, and some live in colonies of 6,000 nests,” the research assistant professor in the School of Natural Resources at the University of Nebraska-Lincoln said.

“That is how the story began in 1982.”

Between that first choice and now, the  researcher  found out something huge. She’s rocked the world of evolutionary studies, finding that swallows wings are shinking because of the contact with vehicles.

“If their wings are shorter, they can be much more aerodynamic, they can fly better and they will be more efficient in catching insects,” she said.

The study, named Where has all the road kill gone? was published in 2013, and it brought new data to the Theory of Evolution.

“It speaks to evolution and to natural selection because birds that are more aerodynamic and have shorter wings are the ones who are going to reproduce and pass their genes to next generation and they will survive better,” Brown said.

These birds spend the winter in Argentina, Paraguay, Brazil, and Uruguay.

“They spend about three months of the year here, probably three months migrating south, three months there and three months coming back north,” she said.

A specific characteristic of the cliff swallows, although, is that they go all the way south flying over land. All the other birds fly across the Ocean.

“The reason is that cliff swallows eat insects all the way, so as they fly south they feed,” Brown said.

As these birds fly over land, they are constantly in contact with vehicles because they’ve changed where they live because of people.

“As people began to build roads, interstates, and bridges, they made the transition,” Brown said. “Nesting on the cliffs is more exposed, so they moved over to these concrete stuffs, where they were more successful and protected.”

Because of the contact with vehicles, cliff swallows were easily killed. In 1996, there was a snowstorm in the end of May in Nebraska, and many of the birds starved to death.

“We collected the dead ones and measured their wings. Then we asked the question: in this really bad weather, who are the birds that live and who are the birds that died?” Brown said.

The mean wing length of the birds that survived in 1996 was 106.87 ± 0.07 mm and for those that did not survive was 107.53 ± 0.06 mm

The mean wing length of the birds that survived in 1996 was 106.87 ± 0.07 mm and for those that did not survive was 107.53 ± 0.06 mm

After analyzing and comparing dead and alive birds the result was that “swallows that did survive to that weather in 1996, the skeletons were much larger, their wings were much shorter and they were perfectly symmetrical. The birds that did not survive, their skeletons were smaller, their wings were longer and they were much more asymmetrical,” she said.

Neo-Darwinism Theory explains evolution as the result of a number of factors, such as mutation, gene flow, natural selection, and genetic drift.

“Neo-Darwinism lies as justification of the study”, said Marcia Malosso and Luis Roberto Santiago, Brazilian biologists who study birds migration process in the Southern Hemisphere.

“Mutation is the result of swallows long-winged, intermediate-sized, and short wings; gene flow appears through introduction of genes promoted by the same species of swallows migrants from other regions; natural selection (stabilizing and directional); and perhaps genetic drift could be involved.”

The mutation hasn’t brought any damages to the species yet, but Brown highlights that cliff swallows are long distant migrants. If they have shorter wings they may be better aerodynamically, twist and turn, catch insects, and be more acrobatic. However, if they are flying from Nebraska to Argentina, they might be less efficient.

“That is just hypothesizing, it is a guess,” Brown said. “That could happen or not. If there is going to be a problem, that is what I guess it would be.”

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