Birds can become a serious problem on vegetable and fruit farms, plucking corn seedlings from the soil and feeding on ripening fruit. Because of the steep financial losses caused by their feeding, farmers have employed a wide range of tactics to repel and frighten birds. They range from low-tech strings to expensive booming cannons and elaborate netting setups.

But these devices won’t work unless they are employed with an understanding of the birds’ behavior. Farmers must first identify the bird species, as different species respond to different techniques. Second, observe the birds’ behavior and get to know their patterns – when they arrive in the garden, where they come from, where they roost. Once you know the birds’ habits, you can put together a plan to repel them.
The most important factor in repelling birds is to be ready with your prevention program before they start feeding on the crop. Once birds have tasted the food source, they are almost unstoppable.
Although there are dozens of repellent methods for birds, here are the most commonly used approaches, going from cheap and low-tech to expensive equipment.

Fishing line
Recent research has turned up a surprising solution to bird problems: monofilament line. According to James A. Knight, Extension Wildlife Specialist at Montana State University, “The actual reason that monofilament line repels birds is not clear. It has been speculated that because monofilament line seems to appear and disappear, birds are repelled by the uncertainty of whether a barrier exists or not. Perhaps the fear of becoming entangled is part of the deterrent. The monofilament line does not pose a physical barrier to the birds and the lines are spaced far enough apart that the birds could easily pass between strands.”

The monofilament line method is relatively new and has not been fully tested. Recommendations about optimum size line and spacing are still being developed. The technique works best on sparrows, but it did not repel robins and starlings in New Mexico and Nebraska studies. Still, it’s cheap enough that farmers might want to do their own trials.

Knight recommends that you use 20-pound test line, which you can buy any place fishing supplies are sold.
For row crops, the monofilament line should be suspended directly above the row before seedlings emerge from the ground. Anchor it at each end of the row, and as the plants grow, gradually pull the stakes at the ends of the row out of the ground to keep the monofilament about 1 inch directly above the seedlings.
For fruit trees and berry bushes, erect poles that are 2 feet taller than the trees, and string the monofilament line from the top of the pole to the ground, teepee style. Birds are repelled up to a foot away from the line, so it won’t matter if branches stick out a bit beyond the teepee of fishing line. The same thing can be done with berry bushes. See illustration below.

For bedded plants such as strawberries, string the line 2 inches above the plants at 12-inch intervals. “This allows berries to be harvested as they ripen, and still provides sufficient concentration of the monofilament line to repel birds that might be feeding on the berries,” Knight said.

Kites and balloons
Flying, hovering objects that tap into birds’ fear of hawks have been known to be effective at repelling most species. The key to their success is preventing the birds from getting habituated to the flying objects.
One option is the Allsopp Helikite, a combination of kite and mylar helium balloon. The helium keeps the kite aloft, and it dives and moves around with air currents.

Jim Crawford of New Morning Farm in Pennsylvania, uses a Helikite to keep crows out of seedling corn. He has been using it for four years with complete success, he said. Because he does many plantings of corn, he keeps the kite in the field for eight to 10 weeks, yet the birds have never gotten accustomed to it.
The company claims that one Helikite can keep birds away from 1 to 25 acres, depending on species of bird and the crop being protected. One Helikite costs about $200 plus the helium to fill the balloon. See the supplier list on page 16 for more information about Allsopp’s Helikites.

Another material designed to scare birds away is mylar “flash tape,” which can be strung above crops. As it moves in the breeze, the shiny surface flashes enough that birds are afraid to approach. The tape is about $5 for a 300-foot roll. Yellow flash tape is made to repel blackbird species, and black-and-red tape is for a wide range of species.

Scare-Eye balloons are beach balls with big eye shapes on them, and they can be hung on poles throughout the crop field at a rate of six to eight per acre. Birds become accustomed to them quickly if they are left in place, so biologists advise that you move them around every day and take them down as soon as the crop is harvested. According to researchers at the Ontario Ministry of Agriculture, Scare-Eye balloons work best against blackbirds, and sparrows and finches to a lesser extent. But robins and cedar waxwings are barely repelled at all.

Stuffed owls, snakes, and hawks work for only a few days before birds become accustomed to them, they said.

Noise repellents
Big fruit and seed farms in the West often use propane-fired cannons set to go off at random intervals to scare away flocks of birds. The problem with cannons is that they annoy the neighbors, and may not be practical for any but the most remote market farms. Similarly, there are scare bomb devices that shoot fireworks at random intervals.

Another acoustical repellent broadcasts distress signals for blackbirds, sparrows and starlings. Farmers have reported that these devices attract hawks, which are even more frightening to small birds.

Whistling pistol cartridges are often used at airports to disperse flocks of birds, and they are popular with some farmers, too. The farmer shoots the cartridge from a pistol toward the flock of birds. There is a long whistling sound, or a delayed bang. They are more effective than just shooting at the birds with shotguns, which may be illegal anyway.

Netting
Finally, the ultimate solution when repellents have failed is to cover the crop with bird netting. Poles are usually erected at the corners of the fruit area, and wire strung between poles to form a grid that will support the net. Once the net is draped over the support system, it has to be buried along the edges to keep the birds from getting underneath.

Use more than one
According to the Ontario Ministry of Agriculture, using only one deterrent method usually will not work. Multiple methods must be employed to discourage birds. Here are some points the ministry recommends growers keep in mind:
•Use scaring methods in combinations that disrupt the bird’s sense of sight, sound and instill fear.
•New and unfamiliar control methods work initially, but decline in effectiveness over time.
•Random, unexpected noise is better than patterned noise.
•Position more scaring devices along the perimeter of the field, near trees and ponds and along the flight pattern entry areas.