Saturday, March 27, 2010

Do American Robins Find Food by Sight or Sound?

I've been seeing American Robins all winter long, particularly in the Lower Chippewa River bottomlands over by Meridean, Wisconsin.

When I heard the familiar "cheer-a-lee, cheer-i-up, cheer-i-o" song in my yard for the first time this week, I did a double-take... was that a robin?  Singing?  Yes!

The robin is one of a handful of birds most children can identify by sight.  Here in Wisconsin, that may be due to the fact that the American Robin is our state bird - and therefore part of the "state symbols" class taught in most elementary schools.  (I volunteer in the local schools and never cease to be amazed by how little the students know about birds).

Other animals most Wisconsin school kids know:  badger (the official state "animal"), white-tailed deer (the official state "wildlife animal" - a "classification" that's new to me) and the honeybee (the official state insect).   And in case you were curious, the state dance, adopted by the legislature in 1993, is the Polka.

But I digress - back to the robin in my yard...

I sat in my Prius and crept up on the bird.  (Yes, my neighbors probably wonder about the strange person who drives on the lawn).  I wanted to get a photo of a robin pulling up an earthworm.  I had to settle for a robin out on a limb.

As I pulled the Prius back on to my driveway, I found myself wondering:  How do American Robins find worms?

Somewhere in the back of my mind, I recall seeing an image of a robin, tilting its head to the ground.  The caption under it read:  robins listen for earthworms.

Yes?  No?

Unsure, I "googled" and found two answers.  Most of the references on the internet agreed:  robins "look" for earthworms.  Only one reference reported that robins may also use their sense of hearing when hunting worms.

The "looking" reference was the Birds of North America "American Robin monograph #462" by Sallabanks and James (1999):

"When foraging for earthworms, [the robin] uses a combination of "head-cock" and "bill pounce" behavior (Heppner, 1965).  In head-cocking, one eye points towards a spot on the ground, 3-5 cm directly in front of the bird, along the longitudinal axis of the body.  After holding this position a few seconds, the robin rotates and flexes its head to bring the other eye into a similar relationship with the ground.  Bill-pouncing then occurs, whereby the bill is thrust quickly into the ground, presumably at visually detected prey, at the spot where the eyes had been directed."

Montgomerie and Weatherhead reported in How Robins Find Worms  (Anim. Behav., 1997, 54, 143-151) that in a series of controlled experiments, four American robins found buried mealworms in the absence of visual, olfactory and vibrotactile cues, suggesting that robins could use auditory cues to locate the prey.  The authors offered the explanation for the apparent disagreement: 

Heppner’s (1965) carefully conducted experiments showed, in fact, that robins were able to capture earthworms, when they could see them, in the absence of auditory and olfactory cues. He did not directly test whether they could use these other cues in the absence of visual cues.

So... next time you look at the lawn and see a robin cocking his head, he may be looking... or listening... or looking and listening for a worm.

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