Posts Tagged: birds
Natural habitat maximizes the benefits of birds for farmers, food safety and conservation
A supportive environment can bring out the best in an individual — even for a bird.
After an E.coli outbreak in 2006 devastated the spinach industry, farmers were pressured to remove natural habitat to keep wildlife — and the foodborne pathogens they can sometimes carry — from visiting crops. A study published today from the University of California, Davis, shows that farms with surrounding natural habitat experience the most benefits from birds, including less crop damage and lower food-safety risks.
The study, published in the Journal of Applied Ecology, was conducted at 21 strawberry fields along California's Central Coast. It found that birds were more likely to carry pathogens and eat berries without surrounding natural habitat.
The authors said a better understanding of the interplay of farming practices, the landscape, and the roles birds play in ecosystems can help growers make the most out of wild birds near their fields.
“Bird communities respond to changes in the landscape,” said lead author Elissa Olimpi, a postdoctoral scholar in the UC Davis Department of Wildlife, Fish and Conservation Biology at the time of the study. “As birds shift in response to management, so do the costs and benefits they provide.”
The single most important driver
The study looked at how different farming practices influenced the costs and benefits that wild birds provided on the strawberry farms. The scientists combined nearly 300 bird surveys and the molecular analyses of more than 1,000 fecal samples from 55 bird species to determine which birds ate pests, beneficial insects and crops, and carried foodborne pathogens.
They also ranked birds to see which were more likely to bring benefits or costs to farmlands. Barn swallows, for instance, got a “gold star” in the study, Olimpi said. Their mud nests are commonly seen clinging to the underside of barn eaves, from which they fly out to swoop over fields, foraging on insects.
But rather than resulting in a list of “good” and “bad” birds, the study found that most bird species brought both costs and benefits to farms, depending on how the landscape was managed.
The presence of natural habitat was the single most important driver differentiating a farm where wild birds brought more benefits than harm.
“Nature is messy, and birds are complex,” Olimpi said. “The best we can do is understand how to take advantage of the benefits while reducing the harms. Growers will tell you it's impossible to keep birds off your farm — you can't do that and don't want to from a conservation perspective. So how can we take advantage of the services birds provide?”
Win-wins for birds and farms
The study is one of several publications from UC Davis Professor Daniel Karp's lab highlighting the environmental, agricultural, and food safety impacts of conserving bird habitat around farms. A related study in 2020 found that farms with natural habitat attracted more insect-eating birds — and fewer strawberry-eating birds — so that farmers experience less berry damage on farms with more habitat nearby. Such habitats also bring greater numbers of bird species to the landscape.
“All together, these studies suggest that farming landscapes with natural habitat tend to be good for conservation, farmers, and public health,” said Karp.
Additional co-authors of this study include Karina Garcia and David Gonthier of University of Kentucky, Claire Kremen of UC Berkeley and the University of British Columbia, William E. Snyder of University of Georgia, and Erin Wilson-Rankin of UC Riverside.
The research was funded by the USDA and UC Davis Department of Wildlife, Fish and Conservation Biology./h3>/h3>/h2>
Hedgerows bordering farmland – plantings with native trees, shrubs, bunch grasses and wildflowers – support bug-eating birds, which helps with on-farm pest control, according to research by recent UC Davis graduate Sacha Heath and UC Cooperative Extension advisor Rachael Long. The study was published in the October 2019 issue of the online journal Ecosphere.
The authors glued codling moth cocoons to walnut tree trunks and covered some with cages that exclude birds to test the effect that bird predation has on controlling moth pests. If moths emerge from cocoons, they produce larvae that feed on the nuts the following spring, causing significant and costly damage to the crop.
“Permitting bird access to cocoons during the wintertime increased codling moth predation from 11% to 46%, and predation increased with an increasing amount of natural habitat within 500 meters (one-third mile) of the orchard,” the researchers wrote.
Long was not surprised by the finding. She often walks in her family's almond orchard, where a large hedgerow of native California plants grows on the field edge.
“When I walk past the hedgerow,” she said, “I hear birds singing. I see white-crowned sparrows, goldfinches and mocking birds. It's so alive. It's really important to provide habitat to ensure birds have a place to live on farms.”
Songbirds are voracious predators of bugs, including aphids, whitefly, scale, caterpillars, ants and earwigs, especially early in the season when they are feeding baby birds.
Heath said they were surprised to find that the walnut orchards also provided habitat for birds. Woodpeckers and codling moth reduction were highest in orchards where big, old walnut trees were retained.
Currently, 34% of earth's arable land is managed for agriculture. With the human population projected to reach nearly 11 billion by 2100, increased food demand will require increased agricultural area and intensity that will further diminish birds' natural habitat. Providing habitat along field crop borders benefits songbirds, which in turn helps farmers with natural pest control on farms.
Above, a Nuttall's woodpecker eats an experimental codling moth (Cydia pomonella) larvae in a California walnut orchard. (Video: Sacha Heath)
Birds' suffer a reputation as agricultural pests. But Long said that planting hedgerows along field edges won't attract more pest birds.
Heath added, “Insect-eating birds – like chickadees, nuthatches and woodpeckers – move along hedges, riparian streams, old oak trees, and among crops to feed on pests.”
Maintaining hedgerows of native plants on farms has the side benefit of attracting natural enemies and native bees for better pest control and pollination in adjacent crops.
Long is a technical advisor to the Wild Farm Alliance, which, with Heath and Sara Kross, recently published a book on birds' role in pest management. The book, Supporting Beneficial Birds and Managing Pest Birds, is available for free download from the alliance's website. A recording of a webinar on the same topic can be viewed at eOrganic.
Heath is now a biodiversity post-doctoral fellow at the Living Earth Collaborative in Missouri.
Across the globe, scientists have shown that birds can be farmer allies. Insectivorous birds feed on damaging insect pests in many crops including coffee, cacao, oil palm, corn, cabbage and apples. Raptors, including hawks and barn owls, feed on rodents, including gophers, voles and mice (see blog, Barn owls help clean up rodents naturally).
Despite this deep historic knowledge that birds are important predators of crop pests, over time the perception of birds as natural enemies of pests has been generally replaced with the idea that birds are often major crop pests themselves. Indeed, some bird species — like some types of insects — can cause trouble for farmers, but many others — especially those that eat insects and rodents — can be beneficial.
Do birds control insect pests on farms in California's Central Valley?
They do! Recent studies by Dr. Sacha Heath, UC Davis, and Rachael Long, field crops and pest management advisor, UC Cooperative Extension, showed that birds help control insect pests in walnut orchards. Dr. Sara Kross (UC Davis postdoctoral alumnus, now with Columbia University) showed that birds help control alfalfa insect pests.
Birds are voracious predators of codling moth pests in walnuts
Codling moth is a major worm-like pest that infests walnuts, apples and pears. The larvae go dormant during winter, living in cocoons in crevices in trees. Adult moths emerge in the spring, lay eggs and infest crops.
We evaluated bird predation of codling moth using “sentinel prey” and exclosure cages. We glued codling moth cocoons to walnut trunks and covered them with cages, allowing insects and spiders to access the cocoons, but not bird predators. This allowed us to count how many larvae were eaten inside and outside of the cages to estimate pest reduction by birds.
What did we find?
Natural enemies, like parasitic wasps and lacewings, alone reduced codling moth larval numbers by 11%; adding birds into the pest control system reduced them by 46%! Nuttall's woodpeckers and white-breasted nuthatches did a lot of the work; these birds travel up and down the trunks of trees, searching for insects.
Above, a white-breasted nuthatch preys on a codling moth larva “sentinel cocoon” on a walnut tree. Video by Sacha Heath.
Alfalfa weevils are no match for insectivorous birds
Alfalfa weevils are key pests of alfalfa, reducing yields and hay quality if left uncontrolled. Dr. Sara Kross looked at bird predation of this pest by excluding birds from alfalfa plants via cages, and counting the number of weevils inside and outside the cages. She found that birds reduced the number of weevils by more than 30%, showing their importance in helping to protect alfalfa from this serious pest.
Does field edge habitat, like hedgerows, help attract beneficial birds?
Yes! Hedgerows are important habitat for beneficial birds, serving as nesting, foraging and roosting sites. In a study in the Sacramento Valley, crop margins with hedgerows, tree lines and riparian buffers harbored up to six times more birds and up to three times more bird species than bare or weedy margins.
Walnut orchards adjacent to hedgerows and riparian areas had higher numbers of beneficial birds along with more species. In alfalfa, there were more beneficial birds in fields when at least two tall trees were present along the field edges. More beneficial birds were associated with better pest control, that is, fewer codling moth cocoons and alfalfa weevils.
Birds have large territories, fly long distances, and are influenced by what happens on the farm as well as by what happens in the landscape around the farm. For example, we found that codling moth predation by birds greatly increased in walnut orchards as the amount of habitat in the landscape around the orchards increased (including hedgerows, tree lines, riparian and oak woodlands, and grasslands).
Will hedgerows increase the numbers of pest birds?
Pest birds are present on farms regardless of field edge habitat (such as weedy vegetation or hedgerows). Cases will be different, depending on the crop, but in the fields and orchards of Yolo County, researcher Hillary White (formerly with UCCE and now with U.S. Fish and Wildlife) found that three of the most common avian crop pests (American crow, red-winged blackbird and Brewer's blackbird), were up to 10 times more abundant in agricultural fields with bare or weedy margins than in fields with hedgerows.
What can I do to attract beneficial birds to my farm?
Our avian research team has been quantifying the conditions under which birds are helpful or harmful to growers. We are looking for ways to help farmers create bird habitat on their farms to harness the beneficial pest control services birds can provide, while also protecting crops from the damaging effects of some bird species. This information is available in the new publication “Supporting Beneficial Birds and Managing Pest Birds,” co-authored by the Wild Farm Alliance and Drs. Kross and Heath, and technically advised by UC Cooperative Extension and several farmers. This is a user-friendly guide for farmers and conservation practitioners, with the goal of co-managing farmlands for biodiversity and farming.
A white-breasted nuthatch preys on a codling moth larva “sentinel cocoon” on a walnut tree. (Video still: Sacha Heath)
About 35 percent of the food we eat depends on the assistance of bees to pollinate plants and trees so they will produce fruit, nuts or vegetables. It takes 1.6 million colonies of honey bees to pollinate California's 800,000 acres of almond trees.
Our food choices would be dramatically reduced if bees weren't around to pollinate. To illustrate what the produce section of a grocery store would look like in a world without bees, Whole Foods Market removed the products that depend on pollination from one of its stores and took a photo. See the difference: http://ucanr.tumblr.com/post/84164840510/kqedscience-whole-foods-shows-customers-the. Without bees, more than half the fruits and vegetables were eliminated.
Honey bees and other pollinators are being threatened by the drought, disease, mites, loss of habitat and food sources, according to Eric Mussen, UC Cooperative Extension specialist in the Department of Entomology at UC Davis and bee expert.
Beth Grafton-Cardwell, UC Cooperative Extension specialist in the Department of Entomology at UC Riverside and director of Lindcove Research and Extension Center, talks about the role of pollinators in California agriculture in this video: http://www.youtube.com/watch?v=8suOt5PnzWc&feature=youtu.be.
To see photos of different kinds of pollinators and to learn more about how to help them thrive, visit our pollinator page. On May 8, help count the pollinators in your community and add them to the map at http://beascientist.ucanr.edu.