Avian use of hedgerows and adjacent crops in Central California agricultural landscapes

Background/Question/Methods

Hedgerows provide valuable ecosystem services including air and water quality protection, soil erosion control, promotion of pollinators and other beneficial insects, and biodiversity. Planting hedgerows at field margins is an increasingly common conservation measure in heavily transformed agricultural regions of California. Hedgerows may also provide critical habitat for numerous avian species that utilize the small, linear, wooded patches for resting, foraging, wintering and breeding. However, avian usage of hedgerows in Central California has not been well studied and farmers fear they may attract undesirable bird species. More complex vegetation structure and composition attract numerous songbirds that frequent field edges, but there is little information about the degree to which hedgerows are used by wintering and breeding birds. We used a paired study design to 1) evaluate the degree to which hedgerows are used by birds relative to nearby unenhanced field margins; 2) evaluate bird use of adjacent crops (standardized by crop type) to determine if hedgerows attract bird species considered crop pests, 3) determine if hedgerows in agricultural landscapes increase avian diversity and abundance relative to landscapes without hedgerows and 4) quantify and determine key habitat structures that are influencing the avian community on our sites.

Results/Conclusions

The pilot phase of our study was conducted during winter (Nov-Jan 2011) and spring (Apr-Jun 2012) to determine wintering and breeding bird use on paired hedgerow and reference plots in Yolo County, CA. We quantified vegetation diversity, composition, structure, and noted fruiting and flowering events to include in avian-habitat relationship models. Analysis of pilot data indicate that more than twice as many bird species and nearly four times as many individual birds use habitat created by native-planted hedgerows as opposed to unenhanced field margins. Our results also show that species richness, abundance, and bird use in adjacent crops was not significantly different when hedgerows were present, indicating that hedgerows are not attracting pest bird species. Additionally, results indicate that planting hedgerows with native species may act as refugia for wintering songbirds without attracting species considered to be crop pests. These results may help act as an incentive for farmers and landowners to replace non-native field margins with native species, which in turn, provide valuable ecosystem services. We anticipate that survey efforts will continue and expand to further understand the role that hedgerow vegetation structure and composition plays in structuring avian communities in agricultural landscapes.