The Michigan research team erected kestrel boxes in a cherry orchard in 2012. (Courtesy Rebecca May)

After three years of studying the problem of bird damage in tree fruits and grapes in Washington, Michigan, California, New York, and Oregon, researchers haven’t found any magic solutions, but they have reached some interesting conclusions.

One is that bird damage, in terms of the volume of fruit eaten or otherwise ruined, remains pretty much the same year to year. Bird numbers are fairly constant and they need to eat about the same amount every year. But the percentage of damage will vary depending on how big the crop is.

Growers may not notice the damage as much in years of big crops. But in years of small crops, the birds can strip orchards and vineyards of most of the fruit.

Growers certainly noticed this in Michigan and New York in 2012, the year big freezes wiped out most of the crop. The remaining small amount of wild and cultivated fruit barely fed the birds.

Dr. Catherine Lindell, a zoologist from Michigan State University, is the leader of a Specialty Crop Research Initiative funded at $2 million in 2011. The project includes 21 researchers at six institutions. For the last three years, she has reported results of their work during the Northwest Michigan Orchard and Vineyard Show. Growers around Traverse City endure bird damage, and several cooperated closely with Lindell and her colleagues in their study.

In 2012, the first year of data collection, a frightening picture emerged as birds creamed off 25 percent of the sweet cherry crop in some blocks in New York and up to 20 percent of the tart cherries on some blocks in Michigan. But those were very short crops, often left unharvested, so growers mostly ignored the bird damage.

In the big crop year just past, damage was very low, she said, in all the crops they studied—tart cherries, sweet cherries, Honeycrisp apples, blueberries, and wine grapes. Damage reached 3 percent in the most pressured sweet cherry blocks and up to 5 percent in similar Honeycrisp blocks, but mostly damage was less than 1 percent.

Researchers from Michigan State University, Cornell University in New York, Washington State University, Oregon State University, the USDA National Wildlife Research Center in Colorado, and Trinity Western University in British Columbia conducted the studies.

They worked closely with growers. They did a damage survey of 1,590 orchards and set up study blocks on 50 growers’ orchards and vineyards. Details about the project and the participants, and their findings, are on the website birddamagetofruitcrops.info.

At that website, you can, for example, see pictures of the most common nuisance birds and listen to their calls, recorded by the Michigan State University Avian Vocalization Center. While some of the fruit eaters are the much-unloved European starlings, American crows, and ring-billed gulls, they also included songbirds, such as robins and cedar waxwings, and geese.

Shooting

As part of the study, consumers were asked if they would pay more for fruit if growers used bird management techniques other than shooting. Consumers seemed more positive toward other means, using natural predators like falcons, kestrels, and barn owls.

In the grower survey, they were asked what kind of bird damage control methods they used and how effective they were. Many of the growers use some method of damage control, and Lindell found that without such efforts, damage is much higher.

Growers ranked netting as the most effective method, with 65 percent saying nets were moderately or very effective. But lethal shooting ranked second at 55 percent effective.

Growers also used chemical repellents (38 percent effective), trapping (32 percent effective), visual scare devices (25 percent effective), and predator nest boxes (37 percent effective).

Auditory scare devices won a high rating (45 percent), but only a few found them highly effective, apparently reflecting growers’ finding that noise works for a while, but then birds become used to it.

As part of the study, one researcher made video recordings of 16 nesting pairs of American kestrels to see what they brought to the nesting boxes to feed their young. She estimated that the 16 pairs consumed 30,000 large insects such as grasshoppers, 1,300 rodents including voles, and 760 birds during the season.

“Making orchards and vineyards raptor-friendly seems like a promising addition to integrated pest management of insects and rodents, as well as fruit-eating birds,” Lindell said. “The nest boxes for kestrels are easy to maintain, the kestrels are readily attracted to them, and predator birds like kestrels, owls, and falcons scare away many more birds than they actually attack and kill.”

She thinks, in fact, that a promising method would be to use unmanned aerial vehicles (UAVs, or drones) that would mimic the role now played by falcons.

Other high-tech approaches, like lights and lasers, have not been consistently effective deterrents, although lasers used at night seem effective against geese.

The use of air dancers, those inflatable tube men that whip and flap, also did well. One grower in Maryland, Nathan Milburn, reported during the Mid-Atlantic Fruit and Vegetable Convention that he used them effectively to ward off robins and starlings.

The birds will become accustomed to them, he said, but moving them about and changing the color kept them effective all season. The effect of moderate wind accentuated the random flapping and made them even more effective, he said.

Losses

One key part of the project was to quantify fruit damage and quantify the effectiveness of management practices.

In the survey of growers, they found that sweet cherry growers believe that, on average, they lost 13 percent of their crop to birds in 2011, the year studied, varying by state from 5 percent to 32 percent of the crop.

California growers reported spending $2,328 per acre a year for bird management to keep damage down to 5 percent, and believe losses would be three times that without management.

In Michigan, growers spent less ($380 per acre) and suffered more (13 percent losses). New York growers spent $692 per acre, but still estimated losses at 31 percent, by far the highest anywhere.

Oregon growers said they spent $1,069 per acre to keep damage down to 5 percent, and Washington growers said they spend $2,056 to keep damage to 9 percent.

Results were similar for tart cherries. On average, growers said birds destroyed 8.5 percent of their crop, but that varied by state. Michigan and Oregon were low at 5 to 10 percent respectively, while Washington was high at 27 percent. Growers spent from $200 per acre in Washington to $500 in New York to lessen damage.

Overall, growers lose a lot of money to birds.

The study estimated that it cost Honeycrisp apple growers nearly $1.5 million per year in Michigan, $1.4 million in New York, and $26.8 million in Washington.

Tart cherry growers lost $2.3 million per year in Michigan and $1.8 million in Washington, according to the survey.

Sweet cherry growers were the big losers: $12.4 million per year in California, $32 million in Washington State, $2.1 million in Michigan, $3.3 million in Oregon. Growers estimated that bird control measures saved cherries worth between $113 million and $143 million, as losses would have been much higher without them. •