Apr 2, 2015
Strategies take shape for managing birds in orchards

After a major research study to determine the economic consequences of bird damage in fruit crops confirmed millions of dollars in damage in three major regions of the country, the focus is turning toward finding effective deterrents.

Bird species with the most lethal impact on fruit crops include the European starling, finches and the American robin.

Fruit-eating birds commonly eat fruit and feed in commercial orchards. Bird species vary in preferences for and abilities to digest fruit efficiently. Cedar waxwings prefer high-sugar, low-lipid fruits. American robins prefer high-lipid/protein, low-sugar fruits.

Sweet cherries are relatively high in sugar and low in lipids and proteins compared to many wild fruits. Therefore, fruit-specialized waxwings likely use sugar-rich cherry orchards more intensely than robins.

Waxwings visit orchards more often than robins during the cherry season and spend more time in orchards daily and have longer foraging bouts than robins. Habitat use will increase as cherries ripen, more so for waxwings. Habitat use will decline abruptly after cherries are harvested, more so for waxwings.

Bird crop damage is one of the greatest factors influencing growers’ annual profit. A survey of bird damage to Honeycrisp apples, wine grapes, blueberries and tart and sweet cherries determined that bird damage was a “significant factor or most significant factor affecting their profits.”

According to the survey analysis, managing bird damage prevents between $87 million and $115 million in annual crop losses to Honeycrisp grower revenue in five states – California, Michigan, New York, Oregon and Washington.

The survey analysis concluded that unmanaged bird damage to Honeycrisp apples would cause a $142 million loss in the combined outputs of the five states and result in over 2,300 lost jobs.

Average damage per acre ranged from $121 in Oregon to $2,941 in Washington. Per-acre management benefits ranged from $758 in Oregon to $11,606 in Washington.

Catherine Lindell, associate professor in Michigan State University’s Department of Zoology, spoke to growers in February during MSU’s Tree Fruit School in Grand Rapids, Michigan.

“To manage birds in fruit orchards effectively, growers must understand the feeding and movement patterns of target species,” Lindell said. “Our work suggests effective deterrent efforts likely vary for different species. For example, relatively short-duration deterrent efforts may be effective against robins, while waxwing management likely requires more persistent effort.”

She described work in 2013 that compared the effects of using multiple deterrent devices on bird damage levels in Michigan cherries and Honeycrisp apples.

One-acre plots were delineated at opposite ends of a block, separated by at least an acre. One plot had devices (air dancers and kites) that were moved at least every 15 minutes every couple of days, with the matching plot having devices that were stationary.

“When natural and cultivated fruit abundance are higher, damage levels are lower and bird management will be less of a priority,” Lindell said. “When there is less fruit in a given area, there will be more damage to the fruit that is available. Higher damage can be expected in low-yield years, early ripening varieties and in small blocks.

“Blocks near resources that are important to birds are at higher risk for damage,” she said. “Higher damage took place in a (tart cherry) block under wires; edges of blocks; near night roosting sites; isolated blocks with little human activity, and potentially blocks near dairy farms.”

Lindell said researchers have continued to investigate various bird management strategies, including use of kites; units that play predator and distress calls; inflatable tube men and predator nest boxes. All have varying degrees of effectiveness.

Kites are designed to mimic birds of prey. The are cheap ($100 a kite) and always present. The downside: They’re not a real predator; pest birds may become habituated.

The nest boxes produce noise “which sometimes bothers neighbors,” Lindell said. “Kites would sometimes get wrapped around the poles, if the swivel apparatus at the top was too tight. Kites also showed wear and tear by the end of the season.”

Other strategies being investigated by other groups, or under consideration, include light deterrents, unmanned aerial vehicles and falconry. Some of the strategies needing “more study,” according to Lindell, include habitat management, decoy crops and attracting Cooper’s hawks.

Another option is use of falconry, an increasingly popular method being used most in the Pacific Northwest. Growers can pay to have a falconer fly their birds over an orchard or vineyard. While this is a labor-intensive technique, it has achieved its desired results. It offers the ensured presence of a real predator, but comes at a high cost ($20,000 a season).

Air dancer methods were tested at eight sites in Van Buren County, Michigan, in 2013. Across-site comparisons were made with 2012 (with and without dancers). The dancers ran for two to three weeks before harvest, approximately 10 hours per day.

While air dancers can be effective in controlling bird damage, they come with some cautions. The dancers require a power source, they frighten some dogs, and when they are wet, the dancer movements are slower and they blow lower, potentially catching fruit. They also are not aesthetically pleasing in most settings.

Air dancers can run about $325 per setup, using electric hookups or a generator.

Use of American kestrels, the smallest falcons in North America, housed in boxes high off the ground to deter other bird populations – such as destructive crows, starlings and turkeys – showed some positive deterrent capabilities. They are a potential low-cost addition to pest management programs, Lindell said.

Kestrels are highly territorial during nesting (April-August) and defend their nest sites. Many growers use nest boxes to attract wild kestrel. Pro: Small, one-time cost of box installation. Con: There’s no guarantee of box occupancy every year. These boxes are used often in cherries and sometimes in blueberries.

Bird deterrent sprays are another option for growers. Methyl anthranilate and sucrose sprays are the most common. Commercial spray products include Avian Control and Bird Stop.

Lindell said some pilot testing of a netting apparatus proved it to be expensive and labor intensive.

“Each farm is unique and should be assessed for potential risk factors,” she said. “When fruit availability is high, bird management strategies may not be necessary.

“Using multiple deterrents, deploying them early in the growing season and moving them frequently should enhance their effectiveness in deterring birds,” Lindell said.

She said bird management strategies “that are biodiversity friendly, like falconry and predator nest boxes, may be useful in marketing.”

For more information, click here.

Gary Pullano

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