The dreaded bird does not require trees. I have seen them by the hundreds assult a commercial catfish pond of 40 acres in the Miss. delta with no trees within a mile. 100 birds on a pond with 2lb. catfish at 5000 per acre ( thats right 10000 lbs of cats per acre right before harvest}. The cats don't stand a chance and the growers don't like it much. They use fireworks, cannons and guards to chase them off. Some even use mesh nets to discourage the birds.

The bird is not like water birds (ducks) its feathers ( are not water proofed) do not have oil to repell water. That is why they get out of the water to sun by spreading their wings to let their feathers dry after eating. With no oil to impeade diving they dive under water and swim by flapping their wings and feet under water for propulsion. Often they will climb on logs or get in trees to sun. If they don't dry their feathers they become water logged and they have problems. We have not had a problem with them on our ponds but have on the river oxbows. ewest

http://en.wikipedia.org/wiki/Cormorant