Question:

Pigeons congregate around the air conditioning units on the top of our building… they nest under the units and it’s a big mess. What is the best way to stop them from nesting here?

Answer:

Rock Pigeons, the wild ancestors of our common pigeons nest on nooks and sheltered ledges of cliffs. Your air conditioning units provide just the type of sheltered nook that these pigeons are looking for in a nesting site. As long as the birds can get up under the units, it will be hard to discourage them from trying to nest there. Your best bet is to install a netting or some other physical barrier to keep them from being able to get under the units.