From the BBC:
The city council is mounting a campaign to rid the city of the birds, which it says are being fattened up by the public feeding them leftovers.
Ten robotic birds of prey are being brought into the city centre to scare off the pigeons and visitors are being warned not to give them food.
The council wants to encourage the birds into parks and open spaces.
The mechanical birds - called "Robops" - are to sit on the roofs of buildings, and can be moved around.
They look like a Peregrine Falcon, which is a natural predator of pigeons, and even squawk and flap their wings to scare off the birds.
Councillor Berni Turner, Liverpool city council's executive member for the environment, said: "Feral pigeons are a real nuisance in the city centre, they fly up at people and they leave droppings everywhere which not only makes the city look really unattractive but can make surfaces slippery and dangerous.
"We need to get the message across that anyone who feeds the birds intentionally, or occasionally with leftovers such as sausage rolls or burgers, are responsible for our streets being so crowded with these birds."
The pigeons get bigger because their natural diet is seeds and insects, rather than high-fat junk food.
Councillor Turner said it is making them "overweight and gives them a scruffy, unhealthy appearance".
She added: "We want to be able to showcase our city centre in our birthday year and of course in 2008, so it's essential we tackle this issue now and educate members of the public that if there's no food, there'll be no pigeons."
The city council uses the equivalent of 88 man hours a day cleaning droppings from streets and buildings, at a cost of £160,000 a year.
I tried to find a video of the robo falcon in action at the Robop's website but there doesn't appear to be one. There is a dvd you can order, but nothing on the website yet. I love how the site bills it as "the world's first intelligent bird repelling system."
I tried You Tube for a video and didn't find this exact product but did find another robo falcon that does look like loads of fun for someone who would is interested in falconry but just can't get a bird at the moment: