As high tide inundates the muddy shallows of the Fraser river delta in British Columbia, what looks like a swarm of mosquitoes quivers in the air above. Upon closer inspection, the flitting mass turns out to be a flock of small shorebirds. The grey-brown wings and white chests of several thousand Pacific dunlins move in synchrony, undulating low over the water, then rising up like a rippling wave, sometimes for hours on end. Staying aloft like this is exhausting, especially in midwinter when the internal furnaces of these small birds, weighing less than a tennis ball, must be refuelled continuously. But setting down to rest and digest their mud-dug meals in the adjacent coastal marshes comes at a cost: an obscured, fearsome view of lurking predators like the skydiving peregrine falcon. The dunlins won’t alight until the ebbing tide buys them back their safer, open vistas.
The evidence that fear motivates dunlin flocking is circumstantial, but compelling. In the 1970s, when populations of peregrine falcons were depressed due to pesticides, dunlins spent less time flying and more roosting. But as pesticides such as DDT waned due to regulations, more peregrines have returned.
Fear is a powerful force not just for wintering dunlins, but across the natural world. Ecologists have long known that predators play a key role in ecosystems, shaping whole communities with the knock-on effects of who eats whom. But a new approach is revealing that it’s not just getting eaten, but also the fear of getting eaten, that shapes everything from individual brains and behaviour to whole ecosystems. This new field, exploring the non-consumptive effects of predators, is known as fear ecology.
by Lesley Evans Ogden, Aeon | Read more:
Image: Robbie George/The National Geographic Image Collection
