Hedgerows enhance bird abundance and diversity on farms

California’s Central Valley is home to a rich diversity and solid abundance of birds. Many are year-round residents, while others are migrants that winter in our valley or travel to destinations further south. Currently more than 400 species of birds call the Central Valley their home; these include raptors, songbirds, ducks, geese, shorebirds, hummingbirds, and others. (Download a checklist of Central Valley birds here.)

All birds depend on habitat for food, shelter and nesting sites. With a decline in habitat in the Central Valley, primarily due to agricultural expansion, urbanization and water diversions, there has been a significant decrease in the numbers and types of birds. Many bird species are now endangered, threatened or listed as species of special concern. Approximately 36 percent of our state’s historical grasslands, 9 percent of the original wetlands, and 2 to 7 percent of the original riparian forests remain. The Central Valley alone has lost more than 90 percent of the riparian, oak woodland and shrub land habitats.

Despite this loss and fragmentation of habitat, many birds continue to use remnant or restored riparian and upland vegetation around farms. Crops such as rice and alfalfa also provide important habitat and foraging areas for birds. Interest is also surging in restoring lands to enhance habitat for birds, including planting hedgerows of California native shrubs and grasses along field edges.

In a recent study by UC Cooperative Extension and Audubon California in Yolo County, researchers determined that hedgerow plantings along field margins helped increase the abundance and species richness of birds on farms, both for winter migrants and year-round species. Their data analyses, examining farms with and without hedgerows, showed that the presence of hedgerows tripled bird abundance and doubled bird species richness in these linear habitat features, but did not increase the bird abundance in the adjacent crops. Of the 2,203 birds counted during the winter and spring of 2011-12, hedgerows drew 41 species of birds, as compared to 22 species in control areas (weedy, semi-managed field edges). In addition, more than three times as many birds used the hedgerows during wintertime, compared to the spring breeding season. This highlights the importance of this habitat for migrating and overwintering birds.

Of significant interest was the finding that bird pest species were using crops regardless of field edge habitat. That is, crop fields with hedgerows showed the same numbers of bird pest species (such as blackbirds that can damage seed crops), compared to crop fields without hedgerows. The researchers observed a total of 1,642 birds, representing 30 species using the adjacent agriculture fields. The minimal species overlap indicated that a different bird community was using crop fields, regardless of the presence of hedgerows. The researchers also found that crops were more heavily used in the winter than during the breeding season.

Hedgerows provide a variety of ecosystem services in agricultural landscapes, such as attracting native bees to enhance pollination and natural enemies to control pests in adjacent crops. Birds also feed on insects and rodents, potentially helping with pest control in crops. The value of hedgerows on farms for enhanced biodiversity and ecosystem services will hopefully encourage more landowners to establish them on field edges for conservation purposes.

For more information on establishing hedgerows on farms, download the free UC ANR publication Establishing Hedgerows on Farms in California. A more thorough discussion of the study results highlighted in this blog will be published in the upcoming December 2012 issue of the California Society of Ecological Restoration newsletter, Ecesis. A conservation innovation grant from the Natural Resource Conservation Service will help expand and continue this important research.