For some species, neighborhood pride is more about survival than sentiment. Many creatures travel hundreds of miles to find resources before returning home to mate. How do they know where to go? Signature smells and magnetism help migrators, but some parts of the process are a mystery.
Aquatic animals generally just follow currents to open waters, but aromatic awareness comes in handy when it’s time to reverse course to reproduce. Lake sturgeon, for one, hatch in the pebbled depths of Wisconsin’s Kewaunee River and wend up to 100 miles to the Great Lakes, where they mature for a decade or two before the big paddle back. Less than 4 percent settle somewhere new. “They imprint on the river they’re born in,” explains Jessica Collier, a biologist at the US Fish and Wildlife Service in Green Bay. Sturgeon may use their whiskerlike barbels to sense proteins in the water, allowing them to sniff out their route.
Species covering larger distances can tap Earth’s magnetism instead. Arctic terns fly 12,000 miles from pole to pole; loggerhead turtles cruise 8,000 miles from Japan to Baja; and bogong moths flit 600 miles across Australia to winter in caves. The bugs are so precise that they often mate and die on the same stretch of rock where they were born.
Still, the moths don’t rely entirely on the planet’s pull, says Eric Warrant, a zoologist from Lund University in Sweden. He likens them to hikers handling a compass: They set a course with cardinal directions, then adjust based on visual landmarks. But even this multisensory system doesn’t tell the whole story. “Their parents have been dead for three months when they’re ready to take wing,” Warrant says. They’ve never been taught where to go yet somehow inherit the instinct to seek specific waypoints.
Cracking these gene-driven impulses will provide a fuller picture of how more animals navigate, as well as help us assess if DNA-encoded intuition can withstand human changes like dams and light pollution. And if we do get in the way, research can offer ideas for how to help critters get where they’re going.
This story appears in the Spring 2020, Origins issue of Popular Science.