In the warmer months, earthworms comprise about 15-20% of the American robin's diet.
In city parks, backyards and fields, robins can be seen hopping, stopping and tilting their heads before quickly pulling a worm out of its burrow.
How do robins locate their underground prey?
Contrary to popular belief,
robins don't "listen" for earthworms.
Even though robins have excellent hearing (especially for high-frequency sounds), tests have found that robins ignore the low-frequency sounds generated by burrowing earthworms.
Robins don't "feel" earthworms moving around underground either.
Robins use VISION to hunt worms.
Robins have monocular vision- their eyes are on the sides of their head, and each eye is used independently.
Robins will bypass burrows where worms are not within visual range.
A robin tilts its head towards the ground to scan for worms. When it sees movement, it lunges quickly and pulls the worm from its burrow.
But worms don't give up without a FIGHT.
Robins know that the best time to hunt for earthworms is when the ground is wet.
Earthworms breathe through their skin and need damp conditions to keep from drying out.
When it rains, earthworms come to the surface to move around more easily and to migrate. (They do not surface to avoid drowning.)
Even though worms are very slippery, they are tough to pull out of their burrows.
Earthworms' bodies are equipped with tiny bristles called setae. They are arranged in pairs on each segment of the worm's body.
A worm uses its setae to grip the sides of its burrow, making the robin work for his meal.