Pacific Southwest

Title: Potential effects of sudden oak death on birds in coastal oak woodlands

Author: Winslow, Donald E.; Tietje, William D.

Date: 2007

Source: In: Frankel, Susan J.; Shea, Patrick J.; and Haverty, Michael I., tech. coords. Proceedings of the sudden oak death second science symposium: the state of our knowledge. Gen. Tech. Rep. PSW-GTR-196. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture: 305-328

Station ID: GTR-PSW-196

Description: Tree pathogens can affect community composition and structure over wide areas. Phytophthora ramorum, cause of sudden oak death (SOD), occurs in the wild in California from Humboldt County to southernmost Monterey County. P. ramorum has killed many trees at some sites and may spread to affect near and distant forests. The pathogen has not yet been detected in San Luis Obispo County outside of nurseries, but threatens coast live oak (Quercus agrifolia) woodlands there. SOD-induced changes in vegetation structure and tree community composition may cascade to affect vertebrate communities. From 2002-2004 we counted breeding birds and measured habitat characteristics at 78 points distributed among four sites in coastal oak woodlands at high risk from SOD in San Luis Obispo County. Each point was visited three times each year to conduct 10-minute counts of all adult birds detected within 50 m. In 2004 we surveyed trees within 10 m of each point. We found 13 tree species; 63.8 percent of the individuals recorded were coast live oak and 19.6 percent were California bay laurel (Umbellularia californica). We recorded 75 bird species at the census points. The most abundant species were Steller's jay (Cyanocitta stelleri, 8.9 percent of individuals), orange-crowned warbler (Vermivora celata, 8.2 percent), dark-eyed junco (Junco hyemalis, 7.4 percent), and spotted towhee (Pipilo maculatus, 6.8 percent). Avian species diversity (Shannon-Wiener index) showed no clear pattern of variation with basal area of oaks (Quercus spp) and tanoaks (Lithocarpus densiflorus) in 2004 (r_s = -0.10, 0.2 < p < 0.5), but oak titmouse (Baeolophus inornatus) abundance was associated with oak/tanoak basal area (r_s = 0.40, p < 0.001). We used these data to evaluate six habitat association models for cavity-nesting birds. Using QAIC_c as an information criterion, the most favorable model indicated that cavity-nesting birds select microsites with large-diameter trees (Akaike weight = 0.47). Changes in tree size class distribution resulting from SOD may lead to a slight decrease in cavity-nesting bird abundance over time. Effects on individual species may be more dramatic.

Keywords: Quercus agrifolia, avian community structure, cavity-nesting birds, California Central Coast, disturbance, community dynamics

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Citation

Winslow, Donald E.; Tietje, William D.  2007.  Potential effects of sudden oak death on birds in coastal oak woodlands.   In: Frankel, Susan J.; Shea, Patrick J.; and Haverty, Michael I., tech. coords. Proceedings of the sudden oak death second science symposium: the state of our knowledge. Gen. Tech. Rep. PSW-GTR-196. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture: 305-328.