While the cocked-head posture of a robin seeking food does resemble a
"listening" pose, the bird is actually scrutinizing the ground with
one eye, looking for worms or their castings.
"When American Robins are searching food on our lawn with their head
close to the ground, are they listening for worms?
No. Experiments have shown that Robins hunt by sight, not sound. If
you watch them for some time, you may also observe one using its feet
to thump on the ground to try stimulate some movements from the worms
before catching them."
Project NestWatch: Frequently Asked Questions
"The robins hunch over and scoot quickly across the yard, stop, stand
erect and then tilt their head to look for worms. Contrary to popular
belief, they are not listening for the worms, but they are actually
using their good eyesight to see the worms in the grass."
IrritatedVowel: American Robin
"When the robin is searching through the grass to find dinner, all
studies suggest they are doing it entirely visually, not by hearing or
smell. When the robins run along the grass cocking their heads, it
appears that they are listening but all of the data suggest they are
just looking. What are they looking for since many of the worms are
below the surface of the lawn? They look for the castings or pellets
of mud on the soil surface indicating the entrance to a worm hole."
KnowWhat: How birds find worms
"An American robin hops along the lawn, stops, tilts its head and then
grabs a worm. Ever wonder how it found that worm? The robin is looking
for the tips of worms at the entrance to their burrows. Most birds,
like the robin, have eyes at the sides of their heads, giving them a
'wide angle view' of the world. For a good close-up view, however,
they often direct only one eye at their food. Since they can't roll
their eyes as we do, they simply tilt their head in that direction and
may appear to be listening, rather than looking, for food."
Electronic Naturalist: Looking or Listening?
"It was once believed that the robin hunted by sound. However, a
series of experiments done in the 60s, (F.H. Heppner, 1965, 'Sensory
mechanisms and environmental cues used by the American robin in
locating earthworms.', Condor 67(3): 245-246) concluded that the robin
finds its prey by sight - not sound... Apparently, after it rains,
worms rest with just the tips of their bodies showing at the mouth of
their burrows... making them easy targets for the keen eyed robin.
Your observation that the birds appear to cock their heads is
accurate, although they do this to see the worms rather than to hear
them. Unlike owls or hawks, the robin's eyes are positioned to the
side of its head, not in the front. When the bird cocks its head to
the side, it is actually looking down."
MadSci Network: How does a Robin know where the worm is?
My Google search strategy:
Google Web Search: robin OR robins worm OR worms listening
I am a bit embarrassed by these findings: several years ago I was a
Girl Scout leader, and during a nature hike I confidently told my
troop that robins located earthworms by listening for the sounds the
worms make underground. This just goes to show that you can't always
believe everything that you hear from authority figures. ;-)
Clarification of Answer by
07 May 2005 17:55 PDT
My friend and colleague Denco has sent me a link to a study which
indicates that robins may use auditory clues in their quest for worms:
"Birds use auditory, visual, olfactory and possibly vibrotactile cues
to find prey, but vision is the predominant mode of prey detection. In
a series of controlled experiments in an aviary, four American robins,
Turdus migratorius, found buried mealworms in the absence of visual,
olfactory and vibrotactile cues, suggesting that they could use
auditory cues to locate the prey. They also had significantly reduced
foraging success when auditory cues were obscured by white noise.
These results conflict with the only other experimental study of
foraging in American robins, which concluded that they foraged using
visual clues alone."
This makes me feel better about my pronouncements to the Girl Scouts.
However, I can't help imagining the merriment if these kids had known
that the American robin's scientific name is "Turdus migratorius." The
scatological humor would probably have continued for hours.