by Jessica Bern
There are many tools to help manage the birds that can damage a farmer’s crops. With help from Dr. Page Klug, a research wildlife biologist with the USDA National Wildlife Research Center, and Catherine Lindell, associate professor in the Integrative Biology department and Center for Global Change in Earth Observations at Michigan State University, we are offered a plethora of suggestions as to how to make it work safely.
According to Klug, “Successful bird dispersal often involves a combination of tools.” Those include getting tools out early before birds establish feeding areas, understanding bird ecology and biology and, like every endeavor in life, exercising patience and persistence.
Klug places her methods into several categories: population control habitat and modification; exclusion; visual, auditory and physical deterrents; and chemical repellents.
“When you move to the landscape scale, that’s when we have more tools at our disposal,” Klug said. “Where we can start to impact bird distributions is by offering habitat modifications or alternative food resources in the surrounding landscape. This will influence where they’re choosing to forage, roost or make migration decisions.”
However, “this would require coordination with neighbors as landowners do not have the ability to implement methods beyond their own property boundaries,” said Klug.
But, she noted, where farmers have the most control is in the field where they can make decisions about what tools they use, the labor and the cost.
An example is chemical repellents to treat weeds or insects. While in the lab, Klug found you can reduce consumption by using methyl anthranilate. “When it contacts the bird, it will irritate the mucous membranes and have them not want to eat that that crop,” she said. However, “anthraquinone is gustatory, so it must be ingested to have an impact,” she added.
Although pesticides might work on some crops and in some situations, Klug said, she wouldn’t recommend any pesticides or chemical repellents that work for row crop agriculture.
There are several approaches to get the crops off the fields before the numbers of blackbirds are at their peak. Avoid planting vulnerable crops near roosting or breeding habitats, plant larger fields to spread the damage, coordinate with your neighbors, avoid early and late ripening fields, delay planting dates or you can try advanced harvesting.
Finally, Klug delved into the topic of drones, which have the benefit of not needing to work in conjunction with anyone living nearby. “In our captive studies, after utilizing raptor models versus a fixed wing or quadcopter model, we found individual redwing blackbirds will alert sooner and are more likely to take flight in response to a raptor model. They are also more likely to take more time to return to forage if you’re flying at them directly as opposed to overhead,” she said. They also noticed that abandonment peaked later in the day, likely because the birds were tired of foraging. Therefore, Klug concluded, using drones in the morning would likely be more effective.
Lindell discussed the role of birds in managed systems, particularly attracting American kestrels to orchards.
A survey of sweet cherry growers was conducted in Michigan, New York, Oregon and Washington State. The growers were asked to estimate what they were spending to protect their crops and what they estimated they lost through damages.
The growers in New York, where there are a lot of small fields, estimated their current damage as being anywhere from 5% to 31%. They also asked the growers “If you didn’t do anything to try and deter birds, what kinds of damage levels would you then have?”
The low estimate was 13%, but it went as high as 60%. When the growers included the notion that the neighbors also took no preventive measures to try and deter birds, the estimate in New York went as high as 67%; the lowest was in California, at 16%.
Collectively, these five fruit producers in these five states estimated the annual loss at nearly $200 million.
Regarding increasing natural predators in orchards, Lindell was specifically referencing the American kestrel. She had heard that growers of blueberries in Oregon were using kestrel boxes with some success, so she decided to do the same in sweet and tart cherry orchards.
Lindell and her students placed kestrel boxes on towers with the result being that they were almost all occupied by kestrels and almost all had laid eggs. Through tracking kestrels after they left the nest with a camera, they saw the kestrels eating a lot of insects and mammals. Most surprising was the number of birds they ate as well.
As a result of surveys conducted by Lindell and her students, they found that where kestrels were actively nesting in sweet and tart cherry orchards, there were fewer pest fruit-eating birds.
Curious to know how this result would affect the economy, Lindell estimated that over a period of five years, between 46 and 50 jobs could be created because there would be more fruit in the system. If farmers made more money, they could then put it back into their local economy.
Lindell and her students tried this same experiment with kestrel boxes in blueberry fields. They found the number of kestrels was much lower than in the sweet cherry orchards. To compare, from 2016 to 2018, the occupancy average in the blueberry fields was 30%, compared to the sweet cherries, where occupancy averaged around 90%.
“One other factor aside from the different box occupancy rates is that we found in our blueberry production region, starlings were much more likely to use the kestrel boxes,” Lindell said.
A colleague of Lindell’s conducted a focus group with consumers about their views on pest management techniques. The result was that consumers were amenable to using techniques like predator nest boxes or falconry. Lindell explained that some fruit growers will hire falconers to come in and fly falcons over their fields as well as other types of hawks. “Consumers also said they were willing to pay more for fruit produced with these types of management techniques compared to methyl anthranilate,” Lindell said.
She added, “Kestrels are going to be most effective for deterring pest birds when the fruit is ripening. It overlaps with their nesting period. For example, if you have sweet cherries or early variety blueberries, that’s when you get the most benefit.”