Ask Dr. Universe: Robins use sight and hearing to find worms and other things to feast on

Dr. Universe: How do robins find worms? – Jerry, Washington state

Dear Jerry,

I love watching robins. They hop across the grass then pause and tilt their heads to one side. Soon – jab! –they pull a wiggly worm from the soil.

I asked my friend Heather Watts what those robins are doing. She’s a bird scientist at Washington State University.

She told me that robins use two senses to find worms.

“The existing evidence is that they use both visual and sound cues to find worms,” Watts said. “Depending on the environment, they might use one more than the other.”

Sometimes robins see what they’re hunting. They may notice tiny movements in the soil. Or they might spot small holes in the ground–or even a bit of a worm poking out of a hole.

That’s probably why robins tilt their heads while hunting.

Unlike us, robins have side-facing eyes. That maximizes their field of vision so they can scan for predators – like curious cats.

The sharpest vision happens right at the center of a robin’s eye – called the fovea. So, when a hungry robin wants to grab a worm, it tilts its head. That lines up its sharpest focus directly over the patch of ground it’s inspecting.

That pose also frees the other eye to scan the sky for danger.

Sometimes robins hear what they’re hunting. As worms move through soil, their skin rubs against grains of dirt. That makes rustling or crackling sounds. If a worm’s tunnel is wet, it might make gurgling noises. Those sounds are too quiet for humans to hear.

Scientists aren’t sure whether robins rely more on sight or sound. A robin probably uses its eyes in open areas with good visibility. Or when noise – like high winds or traffic – make it harder to hear. If the worms are hidden by grass or rocks, a robin may use its ears more.

Scientists don’t think robins use their other senses to hunt – like feeling vibrations in the soil or sniffing out worms.

It turns out the robins I see outside may not be hunting worms at all. Worms are only about 20% of a robin’s diet. They mostly eat fruit and other tiny invertebrates like insects. But there are times when robins eat lots more worms.

“Worms are a particularly important part of the diet during the breeding season – so spring into summer,” Watts said.

That’s when adult robins are feeding hungry chicks. Worms are a nutritious snack for growing birds.

So, when a robin scans the ground, it might not even be looking for worms. It could be searching for beetles or other tasty finds.

I guess you could say there’s a lot of wiggle room in the process.

Sincerely,

Dr. Universe

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