There must be 50 ways to get rid of pigeons, but not 50 effective ways. New Yorkers have tried broadcasting falcon shrieks, installing beach balls painted with big eyeballs, posting fake owls on cornices, strewing mothballs on roosts, even using Avitrol, a hallucinogenic advice now outlawed in the state, which made birds ‘go on a bad trip’, persuading their pets to stay away.

Our co-op on the Upper West Side is next door to a grocery store. Our back courtyard shares open space with the grocery store’s air vents and cooling system. Pigeons are nesting around the store’s cooling system, providing food for rats. Our co-op hired an exterminator, but so long as the nests remain, the problem continues. The store’s management company has not returned our calls. When we called 311, we received a warning from the city that our building was in violation of health codes and would face fines if the pigeon problem was not resolved. We called 311 again to explain. The operator opened a new service complaint, but we have heard nothing back. That was six months ago. What recourse do we have?

I live in a condominium with beautiful landscaping, trees — and lots of birds. The air-conditioning and heating units in the apartments are vented outdoors through louvers built into the building’s brick facade. Birds nest in the spaces between the louvers and the cooling-and-heating units, leaving behind droppings and nesting material. It is messy and a health hazard, but does not damage the appliances. The board says condo owners are responsible for cleaning and removing the nests. But shouldn’t this be the board’s responsibility, since the nests are in the facade and not in the appliances?