So easy:
"The use of hawks and falcons to remove pigeons and gulls is becoming ever more popular in the UK with raptor-specific companies starting to compete with conventional pest control services for business. The use of a raptor as a pigeon removal option is commonly marketed as a ‘green’ and ‘natural’ method of control that is ‘humane’ and ‘in tune with nature’. It should be fully understood that flying a raptor as a method of control is not a non-lethal method of control, nor is it ‘humane’."
http://www.pigeoncontrolresourcecent...s-of-prey.html