Discouraging pigeons

[Andrij]

Pigeons have discovered the exhaust vent from my boiler and enjoy resting upon it (I presume for the heat).  They like it so much they seem to invite all their friends, and some appear to have taken up permanent residence.  Normally I couldn't care, but their presence has resulted in considerable 'deposits' on my kitchen window ledge as well as on the ground below the window.  Directly below this window is the entrance to the house.

Any suggestions on how best to chase — and keep — them away?  I would guess the latter could be sorted out with some netting, but I don't think the landlord will get around to that until the weather is significantly warmer and dryer.
 

[Wowbagger]

Sparrowhawks, ma'am.

[Manotea]

This is what you want.

[border-rider]

It's probably going to need a physical solution.  Either a plastic sparrowhawk, or some of that sticky-up stuff you can get that's specifically designed to stop pigeons landing on it.

edit: crosspost with Wow on the raptor and Manotea on the spikes

[clarion]

You could start selling the guano

[tiermat]

Shoot one of them then tie-wrap it to the grill, the others will keep away....

[Andrij]

You could start selling the guano

How much do you want, what are you willing to pay, will you come to collect?  
 

[clarion]

No, I don't want any myself, but I shall invoice you for my usual consultancy fee for giving you the idea

[Cudzoziemiec]

Spikes are probably the best idea. You need to do it before they get the idea of building a nest on the window ledge or in some inaccessible (to humans) nook or cranny, as then you'll have feathers, noise and other issues to deal with. They carry a few parasites which also infect humans, so I understand, so it's not good to let them settle in.