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Plant Focus

Quercus skinneri
Quercus skinneri is a Central American oak, distinguished by the large size of its fruit.

Birds and Oaks in California’s Urban Forest

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Daniel A. Airola and Steven E. Greco

Published May 2019 in International Oaks No. 30: 109–116

Abstract

We describe three studies that address the importance of native oaks (Quercus spp.) to birds in the urban forest of Sacramento, California, U.S.A. In one study, we surveyed tree canopy cover and abundance of spring and fall migrant songbirds in an older residential neighborhood. Migrant abundance was strongly and positively correlated with Q. lobata (valley oak) canopy cover, with migrants nearly absent from areas lacking oaks. Migrants foraged in Q. lobata substantially more often (74%) than expected based on its 15% relative canopy cover. In another study, we evaluated abundance of resident and wintering birds across a gradient from young residential neighborhoods to natural woodlands. Urban forest with oak supported eight bird species that were absent from urban forest without oak, and supported substantially higher abundances of eight other species. Highest bird species richness occurred in the mixed oak-riparian community. A third study evaluated acorn harvest and transport by Aphelocoma californica (California scrub-jays) in urban settings. Jays harvested mainly Q. agrifolia (coast live oak) acorns for >121 days and transported them on average >159 m, to a maximum of 665 m, regularly crossing other jays’ territories during transport. They cached an estimated 6,800 and 11,000 acorns at two sites (339 and 845 acorns/season/jay), substantially less than in natural oak woodlands, likely reflecting the increased time required to transport acorns longer distances and the availability of alternative foods. Many seedlings from acorns not retrieved by birds are removed as weeds, but recruitment in less-maintained urban areas provides habitat benefits for other species.

Keywords

urban forest, migratory birds, oaks, Quercus

References

Airola, D.A. 2011. Dynamics of an Urban Turkey Vulture Roost in Sacramento, California. Central Valley Bird Club Bulletin 14 (1): 1-8.

Airola, D.A. and D. Kopp. 2017. Sacramento Purple Martin Nesting Population in 2017: First Increase in 12 Years. Central Valley Bird Club Bulletin 20(3): 81-88.  

Carmen, W.J. 2004. Noncooperative breeding in the California Scrub-Jay. Studies in Avian Biology 28:1-100.

Greco, S.E. and D.A. Airola. 2018. The importance of native valley oaks (Quercus lobata) as stopover habitat for migratory songbirds in urban Sacramento, California, USA. Urban Forestry and Urban Greening 29: 303-311. 

McPherson, E.G. 1998. Structure and sustainability of Sacramento's urban forest. Journal of Arboriculture 24(4): 174-190.

Peper, P.J., K.E. Vargas, and E.G. McPherson. 2011. Sacramento’s Park Neighborhood Trees. Sacramento: StoneBridge Properties LLC. 

Sacramento Tree Foundation. 2007. Guide to Sacramento Oaks. Sacramento: Sacramento Tree Foundation.

Wyly, Z. and E. Teach. 2015. Urban Sacramento Oak Reforestation: 17 Years and 20,000 Trees.  In Proceedings of the Seventh California Oak Symposium: Managing Oak Woodlands in a Dynamic World, General Technical Report PSS-GTR-251, coordinated by R.B. Standiford and K.L Purcell, pp. 447-454. Berkeley, CA: U.S. Department of Agriculture Forest Service, Pacific Southwest Research Station.