My nephew asked why the Robins throw worms in the pond. I know the fish enjoy them and it did remind me of the old photo by Paul Lemmons.
Birds' parental instincts kick in at the sight of small open mouths eliciting an inborn response to feed. The photo shows a Northern Cardinal delivering worms to a goldfish at the edge of a garden pond. The gaping mouths of the fish stimulated the bird. The goldfish, accustomed to being fed at the surface, didn't care who was doing the feeding. To read more go to Birdscope.
Sources: The Birds of North America Online www.bna.birds.cornell.edu and the Cornell Lab of Ornithology Handbook of Bird Biology (see www.birds.cornell.edu/homestudy).