I read with interest your comment about mute swans that "tidy" their habitat.

We have a family of swans on the lake just off our gated community -- Swan Lake Village -- in Markham, Ontario. This year after the cygnets were born the family took to touring around the lake edge, the cob pulling up reeds wherever they stopped. The rest of the family seemed to be content with just eating with no evident connection between these activities.

We also have a feeder to which we call the swans twice a day for a treat of cracked corn and where we can observe them more closely. Romeo, the cob, eats and then does his reed-pulling thing. But he also "cleans" the lake bottom of dead vegetation, pulling up mouthfuls and tossing them aside.

I was wondering if this was related to the tidying or if this behaviour is instrumental in cultivating the vegetation on the lake to help it produce food?