Beneficial birds provide pest control in farm fields

By Bob Johnson. This article was originally printed by the California Farm Bureau Federation.


Western bluebird eating a caterpillar pest. Photo from Glen Bartley/VIREO

Alfalfa growers with trees near the edges of their fields attracted more birds, according to a recently published University of California study, and that resulted in as much as a 30 percent reduction in insect pest damage to the crop.

In another current UC Davis study of dozens of commercial strawberry farms, an abundance of birds led to fewer pests near the center of the field, and only four out of 10,000 berries showed signs of bird fecal contamination.

Ongoing scientific research is calling into question the assumption that birds and other wildlife are incompatible with the safe commercial production of good yields of fruits and vegetables.

"We did some plots excluding birds and found that the birds had very little effect on the strawberries," said Elissa Olimpi, UC Davis postdoctoral researcher. "We did find at the edges they might be eating some of the beneficial insects, but when you get near the middle of the field the birds were providing pest control. The effect of the birds was mediated by insects because there was little bird feeding on the berries."

Olimpi, who is looking at the complex impact of birds as both pests and predators in a study on dozens of commercial strawberry fields, made her remarks at High Ground Organic Farms outside Watsonville during a tour on the eve of the 39th Annual Ecological Farming conference.

The relationship between strawberry production and bird habitat looks to be complex: While fecal contamination of the berries is extremely rare, the birds do reduce beneficial insect populations near trees at the end of the field, but they also help with pest control near the center.

"We hope to come up with management plans that help increase biodiversity and conservation, while also safeguarding health and food safety," Olimpi said.

As she works to develop strategies that are optimal for both the birds and the fruit, Olimpi said she counts on the cooperation of growers like Jeanne Byrne and Stephen Pedersen, who have farmed High Ground for two decades.

"We're often approached by people who do research because they need real farms to test their hypothesis," Byrne said. "We have been part of at least 10 or 15 strawberry studies."

One study Byrne recalled in particular showed that farms that have multiple crops and are surrounded by wilderness areas had almost 25 times as many bees as fields with one crop and no wilderness nearby, and these bees significantly improved the quality of the fruit.

Pedersen's uncle Jerry Thomas was a founding member of California Certified Organic Farmers and he sees High Ground's 40 acres overlooking Harkins Slough as both a place of commercial production and also a precious responsibility.

"It's up to small farmers like us to push the standards," he said.

One new frontier for the latest generation of ecological farmers is finding safe and productive ways to bring birds back to the fields.

Wild Farm Alliance recently published a summary of the complex conclusions from 600 university studies in Supporting Beneficial Birds and Managing Pest Birds, which is available in both a printed version with full color photos and a free online PDF file at the group's internet site (

"Birds can help you or your farm neighbor keep pest insects, rodents and pest birds at bay," said Wild Farm Alliance executive director Jo Ann Baumgartner, lead author of the booklet. "Beneficial birds assist with production in the same way as beneficial insects. When you provide habitat for beneficial birds and bring them closer to your crops, you are increasing your pest-control services."

Supporting Beneficial Birds and Managing Pest Birds includes the latest information on both controlling the pest birds and encouraging the beneficial ones.

"Today, farmers who are masters at integrated pest management are using ecological pest-control strategies that include birds," Baumgartner said. "We think of certain birds as beneficials or as pests, but some species switch roles, depending on the season, their life cycles and the food sources available. Farmers can support these 'turn-coats' in the beneficial phases and deter or co-exist with them at other times."

One unusually detailed study has already shown that birds can play a helpful role in controlling insect pests in conventional alfalfa fields.

"Bird foraging reduced the abundance of the most significant insect pests of alfalfa by over 33%," said UC Davis researcher in the Department of Wildlife, Fish & Conservation Biology Sara Kross, who also helped write Supporting Beneficial Birds and Managing Pest Birds. "The presence of complex edge habitat, at least two trees every five feet, led to higher avian abundance within fields, which in turn led to reduced pest insect populations at sampling points close to the field edge. Fields with complex edge habitat also harbored nearly three times as many bird species as those with simple edge habitat."

This conclusion came after looking closely at the relationships among habitat, bird populations and pest control at dozens of commercial alfalfa fields.

(Bob Johnson is a reporter in Davis. He may be contacted at [email protected].)