After finding dead cliff swallows along the new highways, the researchers began measuring the birds. Then years later, measured more that were killed by a freak storm.
What they found was a revelation:
Measuring each dead bird and comparing them to the birds that remained, the Browns made a surprising discovery. The birds that died had shorter bodies and longer asymmetrical wings. But the birds that lived had larger bodies and shorter wings.
The survivors' shorter wings made them more acrobatic, like a fighter plane. They were able to twist and turn, dodging oncoming traffic, especially larger vehicles like SUVs and Mac trucks. The road kill birds had been less agile.
As Hochman explains, typically we expect evolutionary changes like this to take thousands, or even millions of years, but thankfully for the cliff swallows, they were able to adapt astonishingly fast to match the rapid changes to the American landscape.
Of course, this doesn't mean that our massive system of roads and highways are good for all wildlife – often, the opposite is true – but in this case, it is nice to hear that the swallows have adapted to thrive in our faster, busier and more-congested world.