Bald eagle nesting pairs in the US

It is a curious feature of the universe that as America has worked increasingly hard to restore its most magnificent predator, it has simultaneously become worse at preventing its citizens from being hit by cars. One might imagine these two trends occupying entirely separate corners of human endeavour, yet for sixteen years they have moved together with the kind of synchronisation usually reserved for married couples finishing each other's sentences. The bald eagle, it turns out, is not the only thing making a comeback.

The explanation is almost certainly not that eagles have developed a taste for pedestrians, which is the sort of thing one might suspect after too much coffee. What's actually happening is that both phenomena track the same underlying current: steady American population growth and increased vehicle miles traveled, particularly from 2005 onwards as the recession faded and the economy rebounded. Between 2005 and 2021, the US population grew by roughly 45 million people while vehicle travel increased by approximately 20 percent, and both bald eagle recovery programs and traffic fatalities rose like complementary waves on this tide of activity. The eagle's rebound, meanwhile, benefited from decades of conservation effort finally reaching critical mass, while more people and more cars inevitably meant more opportunities for collisions at the intersections where humans and physics meet.

So we have stumbled upon a statistical relationship that is almost entirely meaningless, which is either the most reassuring or most unsettling discovery possible depending on your mood. It is a humbling reminder that correlation, even at 0.94, can be the universe's way of shrugging at us. The bald eagle and the traffic fatality have nothing to say to each other.