Factors Influencing Nontarget Bird Occupancy of Restored Wetlands in California’s Central Valley

Abstract

Intensively managed restored wetlands and flooded croplands of California's Central Valley support millions of wintering waterbirds. While the benefits to wintering waterfowl are well documented, the effect of intensive management on birds at other times of the year is less clear. Practices such as drainage, mowing, disking and burning may be a nuisance to these nontarget birds at best or life threatening at worst. Alternatively, irrigation over the summer may create habitat that might otherwise be lacking in the dry season. Our objective was to assess the influence of management, adjacent land use, and habitat characteristics on the richness, diversity, and occupancy of birds other than waterfowl in the spring and summer. We conducted 640 bird surveys on restored wetlands managed at varying levels in 2008 (4 April-30 July) and 2009 (19 April-16 July) and used likelihood-based modeling to evaluate occupancy and the relative importance of intensity of management and various environmental factors. Management was not the most important predictor of the richness, diversity, or occupancy of nontarget birds in the summer; rather, variables such as wetland size, vegetation composition, and landscape characteristics were more important for most bird guilds. Contrary to the commonly held view that restored wetlands in California's Central Valley support only wintering waterfowl, they also support a diverse avifauna year round regardless of how they are managed. Bird occupancy and diversity in restored wetlands may be enhanced by creating and maintaining large, complex mosaics of vegetation.