Green

Take Natural Selection and Swallow It

cliff swallow nests
Cliff Swallow nests.
Image: Jay White / Flickr CC

Cliff Swallows are building homes in more and more dangerous places, such as buildings, in between railroad tracks, under bridges, and, as their name suggests, on cliffs.  Somehow, this population of bird is surviving car crashes, and their population is growing rapidly.  Over the span of a 30-year study, the number of nests has grown from 5,000 to 25,000, despite their precarious locations.

What could account for such surprising findings?  Chalk it up to natural selection.  One of the most fascinating findings of the study is tied to the measurement of wing spans in relation to whether they survived or were killed.  Those who were trapped in mist netting had much shorter and sleeker wings than those who were hit by cars.  This suggests that the survivors may have adapted to living in a much busier, urban environment where they need to zip in and out of their homes.

Cliff Swallow
Cliff Swallow
Image: Ken Schneider / Flickr CC

At the same time as this population is growing, other bird species are being hit by cars more often.  Each year, over 80 million birds, of all species, are hit by vehicles.  Yet, the rapid evolution by the cliff swallows is a bit of a surprise to the researchers.

Part of what they noticed is that cliff swallows are excellent observers.  They saw what happened to birds hit by cars and passed on that knowledge to their offspring.

“Over the past year I had begun to intuitively think that we had begun to find less roadkill, so it was then very exciting to go back and find that the math verifies what we were seeing,” said Brown, one of the researchers.

With the human population growing exponentially, there is no question we are expanding into animal territory.   Without the ability to adapt to these changes, some species will likely perish.  However, there could be a trend, like that of the swallows, to gradually grow to live in the fray.

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