Commercial building owners have been plagued by pest pigeons for centuries. Today, in Venice, Italy, an estimated 120,000 pigeons nest in colonies in palazzos, damaging buildings with their corrosive droppings and attacking marble and stucco façades with their beaks.

In the U.S., pigeons create a whole host of problems for commercial building owners. The average pigeon creates about 25 pounds of poop each year. This waste has a high concentration of uric acid that can discolor paint, stain wood, erode metal, even crumble concrete and expensive stonework. Building owners spend millions of dollars annually blasting pigeon poop off hard-to-reach areas using expensive boom lifts and steam hoses.

There are also liability concerns. Pigeon droppings and the twigs these birds collect for their nests can create slip-and-fall hazards around a building’s periphery. Even rooftop maintenance workers can slip and fall on these deposits, creating additional hazards and liability concerns.

On commercial rooftops, pigeons nesting around air conditioning, heating and other air handling systems can wreak havoc with electrical components and mechanical parts. Pigeon waste sucked into ductwork can cause all sorts of operational and health problems. Ventilation systems blocked by bird feces can create a biohazard, circulating infested air to employees and customers. The bacteria, fungi and parasites that live and grow in pigeon droppings can carry and transmit any of 60 known diseases. Even the fleas, mites and ticks that attach themselves to pigeons can carry disease. For building owners who have decided to adopt sustainable energy alternatives, pigeon droppings can destroy the energy gathering capability of solar panels. The droppings can also damage security camera lenses and their rotating drive mechanisms.

Fortunately, there are a number of ways to control pest pigeons around commercial buildings.

One of the most common and effective pigeon control devices is the bird spike. Ideal for rooftops, awnings, gutters, girders, roof peaks and ledges, the spikes keep pigeons from landing. The spikes are often made of stainless steel or rigid U.V.-resistant unbreakable polycarbonate. Harmless to birds, the spikes are usually positioned to cover an entire ledge, and to seal off corners and open sides to prevent clever birds from sneaking around them.

Another highly effective pigeon control option is netting, which when correctly installed, creates a pigeon-proof barrier on rooftops, courtyards, signage platforms and other bird nesting areas. Some manufacturers offer U.V. stabilized, flame resistant, rot and waterproof netting.

Next up is a nifty product called the bird slope. These slippery panels prevent pest pigeons from getting a grip when they try to land. Ideal for ledges, eaves, beams and other 90-degree areas where pigeons tend to nest and roost, bird slope panels are available in a variety of colors to match any buildings décor. The panels glue easily to any surface or they can be screwed onto wood.

Electric-track control systems are another option. These strips discourage pest pigeons from landing with a harmless, buy annoying electric shock. After a few shocks, pigeons simply change their nesting and/or feeding habits and move on. Ideal for ledges, rooftops, and flat or curved surfaces like signs, commercial building owners often prefer electric tracks because of their low-profile design—they’re practically invisible to anyone looking up from below. If you choose this method, opt for a flow-through design to prevent water from damming up on rooftops and other surfaces.

To keep pest pigeons away from large, expansive areas, you can go with foggers and misters. These pigeon deterrents use an aerosol delivery system and are ideal for factories, warehouses, airline hangars, airports, courtyards, and golf courses. Many offer multiple, adjustable nozzles that allow you to zero in on areas that seem particularly troublesome.

For a fast and easy pigeon control alternative, there’s bird gel. You apply it with a caulking gun and when it dries, the gel skins over, leaving a surface that’s tacky and uncomfortable to pigeons. While it won’t harm pigeons, they seem to hate the stuff.

To scare pest pigeons away, many building owners have elected to use motorized whirly-gigs with propeller arms that spin at speeds annoying to birds. These are ideal for parapet walls, roofs, signs, and billboards. Some have batteries, others you plug in, and some are even solar powered.

Less expensive pigeon scare products include flashy banners and balloons, which are ideal for some outdoor areas where their décor won’t conflict with commercial building codes.