I've seen plastic coils of some sort with metal prongs that you unwrap and fix to your ledge/roof to keep pigeons from roosting there. Try your hardware store, or maybe a store that caters to building managers, contractors and supers.

some hardware stores sell fake owls that people may perch on their window sills. pidgeons are frightened by predatory birds, and will not come close to a window occupied by an owl, real or fake.

The pigeon mufflers are the easy part.

The pigeon booties they just will NOT keep on.

Then that's where you should put your air conditioner, which will drown out the noise.

Considering how hot ornamental birds are these days, a well-placed owl could look hot.

How about a BB gun?

The sound pigeons make is not only annoying but their poop is toxic. Ledges and air conditioners covered with poop are health hazards.

I have found obstruction to be the best way to keep pigeons away. I have glued broken pieces of glass to my ledge and it works well. You just need to make sure to put enough pieces. Nails would probably work well too. Although I've never tried those fake owls, according to a pest control expert that I talked to - they are a waste of money.

a "no pidgeons allowed" sign.

How about a low voltage wire across your sill?

I participated in the design on some architectural features for the Belt parkway over the Ocean Parkway Bridge down near Brighton Beach. When the bridge was completed it had become festooned with large broods of pigeons. Upon returning to the site it was clear of birds. Pigeon deterrents were installed, a series of low voltage wires discreetly placed over every horizontal surface. This meant that every I beam had ‘hot’ wire on both sides. The voltage was enough to startle, but not injure and make the birds move elsewhere.

birdbusters-com/bird_control_electric_track.html

A plastic owl won't work. I've seen pigeons perch on the heads of the ones put up in our downtown. Nor will the plastic "anti-bird" mats with flimsy plastic spikes. Use the nasty metal spikes. Moth balls or crystals may or may not work. Look for a commercial bird repellent and keep fingers crossed.

I used a large plastic owl on one window and it did seem to keep them away, but I am hesitant to put them in every window -- especially since it disappeared recently! Assume it was blown away (scary) during one of the nasty windstorms we've had lately, but maybe them tough NY pidgeons wised up and had it "knocked off"!

Curious to see what will happen to pidgeon protections if the bird flu thing really happens around here.

I bough an inflatable owl, which hung tightly on a string moved a little and did a good job of keeping the pigeons away. It also wouldnt hurt anyone if it did happen to blow away.

I had/have a pigeon roosting under my air conditioner that was driving my cat insane. I don't really know if there is a good solution, to be honest. There is something called Stickyfoot or Tanglefoot, but on further research, I found that it basically kills the bird slowly (despite manufacturer claims that it's harmless), which is NOT what I want to do!

Apparently, the owl only works if you move it around every couple weeks. Pigeons aren't as dumb as we think. Plus, my coop would not go for a fake owl on my windowsill, so...

I think that if you put those spiky wire things, you just MIGHT want to paint them green, so it at least reminds YOU of grass, instead of making you feel like rattling you tin cup against the bars of your window yelling, "Atti-CAH, Atti-CAH!"

This is easy. Build a wooden shelf that ***SLANTS*** at a steep angle (like the bike jumps you used to make when you were a kid) and set this securely on the ledge. Don't leave any openings that would allow the pigeons to actually make it their home -- it will need to be a solid structure. This way when the birds land on the sill, they slide off. Best to make the area undesirable, and pigeons need flat surfaces to roost.

Easy,

Start charging rent. Then raise it every year, just hope that the birds don't get a good tennant's lawyer.

Or you could use the spikes and ramps and stuff people noted above.

Not PETA friendly, but a guy when I was in school in England once put some hot peppers out on the windowsill where there were seagulls (they were like pigeons at the school, believe me), and they had a very adverse reaction.

I once read that you should spread a thin layer of Vaseline over your window ledge. It sounds weird but has worked for me. I have only had to reapply once in two years.

Thanks to all of you who wrote in response to my (on behalf of my friend's) question. I hope she applies your advice to her situation. Friends who have visited her from overseas have marveled at the 'bird chorus' which keeps the apartment at a constant volume. One friend even wrote a poem about it.
Happy Thanksgiving!

I had that problem in my first apartment. My father recommended sprinkling red pepper on the ledge and gave me a bottle which said, "Pepper For Pidgons." I thought his spelling was so great, I kept the bottle for years.

i have one on my ac it starts every morning at 4:00 am so we throw a paper ball at it

Anyone who puts glass on a sill to keep pigeons away is sick

I hope you forget it's there and cut your hands to shreds