The giant reed, Arundo donax, is an invasive exotic plant dominant in many of California's riparian areas, and is thought to offer little feeding or nesting habitats for birds. I investigated the relationship between A. donax and riparian bird richness and abundance within three drainages in San Diego county, California during four seasons (winter, spring, and early and late breeding) in 2001. We used aerial photographs and a stratified random block design to select 16 points per drainage with varying A. donax cover. Point counts were used to survey birds and photoplots were used to quantify A. donax cover at each point in each season. We hypothesized that the relationship between A. donax and bird richness and abundance would be negative and would vary by season, guilds (foraging and residency), and cover of other vegetation. Overall bird species richness and abundance decreased significantly as cover of A. donax increased during all seasons and at all drainages. Species richness decreased by 16% to 25% as A. donax cover increased from 0 - 50%. Resident species richness declined significantly with increasing A. donax cover during the winter, spring, and late breeding seasons but non-significantly during the early breeding season. Migrant breeding species richness declined significantly with increasing A. donax cover in both early and late breeding seasons, but migrants were too sparse in winter and spring for analysis. Ground and foliage gleaners showed the same general negative relationship with increasing A. donax cover. An analysis of vegetative and physical factors showed that season and A. donax accounted for 52.5% of the variation in bird species richness. Willow was not a biologically significant factor in a general linear model. The results of this study suggest that removing A. donax from southern California riparian areas would benefit richness and abundance of birds.

Riparian, Arundo donax, Bird communities, Invasive species