Ha! they should try owls-- fake ones work-- but only if they have some moving parts, and, if they get moved once a day or so.. even pigeons figure out the at an owl that never moves is not going to harm them.

several companies sell owls.. the cheap $19 ones don't work to well at all.. the $29 to $49 dollars ones are pretty effective.. and this is on NY pigeons. (commonly referred to as flying rats.) we've also had some success with falcons.. they leave dropping too, but the don't roost on any available edge the way pideons do, and a falcon family eats 2 or 3 pidgeons a day. doesn't seem like much-- but it really good for the building near the falcons nest.. pideons aren't so stupid as to hang around, and wait to become dinner.

one co-op on 5th ave had a falcons nest on a ledge out side its window.. the price of the apartment was higher.(almost 10%)it was a considered an asset!