How Do American Robins Find Worms? Behold the Rich Sensory World of Birds

We all know the early bird gets the worm, but how does he find it? That American Robin in your neighborhood park—how did it dig up the juicy nightcrawler dangling from its bill? After all, worms live mostly underground where we can’t see them. 

A study back in 1965 concluded that robins do so exclusively by sight, the idea being that worm burrows provide peepholes into the underground world. Robins seem to peer down into the burrows and jam their bills in those that are occupied, the paper said. 

But three decades later, a similar study reached a much different conclusion: It produced evidence that American Robins rely on their hearing to find buried food. When worms were presented in such a way that the birds could not smell, see, or feel them, the robins still had success. But when white noise drowned out other sounds, the birds had less luck finding food. 

It may well be that robins use both sight and sound to find worms. The answer is a bit fuzzy not only because the phenomenon seems not to have been studied very extensively, but also because, for us humans, the sensory experience of birddom is utterly foreign. “We see the world in a very particular way, which is not shared by the majority of birds,” says Graham Martin, a retired biologist at the University of Birmingham in England who wrote a book about avian senses. “They live in a different world to what we do.” 
 

You or I couldn’t possibly hear a vole tunneling beneath a foot of snow, for instance, but owls can, no problem, thanks to facial discs that function like satellite dishes. Birds can also see ultraviolet light that humans can’t, which makes their world more colorful than ours. And while our eyes face forward, leaving us unable to see most of our surroundings, many birds (especially prey species) have eyes on the sides of their heads, providing a much wider field of view. “We see the world as in front of us, and we move constantly into the world and it disappears behind us,” Martin says. “Whereas the vast majority of birds, they flow through the world.”

So, when we see a robin cock its head while patrolling for prey, it could be that it’s just heard a worm moving beneath its feet. (Worms don’t make sounds themselves, Martin says, but there is some faint rustling as they drag vegetation from the surface into their underground world.) Or, it could be that the bird is pointing one of its eyes to the sky to watch for predators overhead. Robins couldn’t be reached for comment.

Shorebirds, too, hoover up loads of calories from underground, but they use a different approach: The tips of their bills are packed with sensitive nerve endings called Herbst corpuscles that can detect slight changes in pressure. If a worm or mollusk moves through the mud or wet sand surrounding the bill, the bird can feel the vibrations and pluck out the prey. And in this way, birds and people might not be so different after all; a study last fall found that human hands, too, seem capable of a similar form of “remote touch.” 

Kiwis—which aren’t shorebirds but sort of look shorebirdy with their long bills—take a two-pronged approach. Their sensitive bill tips equip them with remote touch for hunting. But they also are the only birds with nostrils at the tip of their bills, meaning they can smell food underground. Weird little guys. 

And then there’s the American Woodcock, which technically is a shorebird, even though it hangs out in the woods. Like its beachier cousins, the woodcock has a long bill tipped with nerve endings—perfect for probing. Also like many of them, it has a flexible bill tip that makes it easier to catch and slurp up earthworms, its staple food. 

But there’s credible speculation that, adept as they are at finding food underground, woodcocks sometimes opt to have their meals delivered. The birds are known for a funky dance that involves putting their weight on one foot and rocking back and forth. It’s widely supposed that the maneuver causes vibrations that beckon worms to the surface for easy picking. 

Sounds a bit strange, maybe, but it makes sense to Martin. In the U.K., he notes, a common game at country fairs is “worm charming,” in which teams compete to coax the greatest number of earthworms to the surface. They typically do so by stabbing a pitchfork into the ground and banging on it with another garden implement. The resulting vibrations somehow draw worms aboveground, possibly because they mimic rainfall. 

It’s all a good reminder that birds live in a rich sensory world and are amazingly deft at navigating it. After all, they’d been doing so for millions of years by the time we arrived on the scene. “Most people think the world as they see it is the way it really is,” Martin says. Birds tell us that we’ve got a lot to learn.