This response was provided by Darryl Coates, Illinois Department of Natural Resources, District Wildlife Biologist.
As a biologist I have this same complaint come up every year in my district. Birds (i.e., starling, crow, black bird) come together in the fall by the 100s or even 1000s to seek roosting sites within municipalities. The first thing I suggest is that you confirm the ownership of the trees.
The owner of the trees has several options:
1.) Do nothing. This is the usual option taken - Justification: This is just a temporary problem.
2.) Pay to have the tree pruned by an arborist to thin the canopy of the tree. This method can be expensive and has limited success in reducing roosting.
3.) Cut down the tree - This is a little more expensive than pruning. It eliminates the roosting site. Very effect in controlling roosting.
Other possible options: Non-lethal harassments of birds. Note: Check with local police and city ordinances before you use any of the methods listed below.
Frightening devices include recorded distress or alarm calls, gas-operated exploders, battery operated alarms, pyrotechnics (shell crackers, bird bombs), clapper devices (Tomko Timer - Clapper), various sound producing devices (battery operated radio hoisted into a roosting tree playing Rock and Roll Music), lights (for roosting sites at night), bright objects, beating on a tin sheet or 55 gallon barrels with a club. Spraying birds as they land with water from a hose, high-pressure water sprayers or a sprinkler mounted in a roosting tree. For additional information, visit our Living with Wildlife Web site.