A bird control spike, also known as an anti-roosting spike or roost modification, is a device consisting of long, needle-like rods used for bird control. They can be attached to building ledges, street lighting, and commercial signage to prevent wild or feral birds from perching or roosting. Birds can produce large quantities of unsightly and unhygienic feces, and some birds have very loud calls that can be inconvenient for nearby residents, especially at night. As a result, bird control spikes are used to deter these birds without causing them harm or killing them.
Described as “the most effective (type of) stand-alone bird deterrent”, bird control spikes can be placed along ledges, walls, on top of commercial signage, closed circuit television cameras and in rain gutters, in order to prevent birds from perching on the surfaces. Bird control spikes are most common in city centres and coastal areas, where feral birds are more common and more likely to come into conflict with humans. Source: http://en.wikipedia.org/wiki/Bird_control_spike