Effects of off-highway vehicles on avian abundance and diversity in a designated vehicular recreation area

More people are engaging in recreation on public lands in the United States than ever before. However, increased recreation can be detrimental to wildlife species. Managers need to understand how recreational activities, such as driving motor vehicles through natural areas, can affect a range of species so that they can balance access to nature with preservation of wildlife communities. We assessed the effect of off-highway vehicle (OHV) use and OHV trail density on the abundance and diversity of bird species across Hollister Hills State Vehicle Recreation Area in California, USA. We collected data during three winter and two spring seasons spanning 2012 to 2014. We used a hierarchical community distance sampling model to compare bird community and species-level abundance for 30 species in spring and 18 species in winter and used raw counts of birds to compare Shannon diversity between OHV use and nonOHV use areas. Community-level bird abundance increased significantly with OHV trail density in both winter and spring and was significantly greater in OHV use areas than in nonOHV use areas during the winter, but not spring. Seven and eight species, in spring and winter respectively, were significantly more abundant with greater OHV trail cover, and none was significantly less abundant. OHV use had no significant effect on Shannon diversity. Thus, OHV recreation appears to have had nonnegative effects on abundance and no discernable effect on diversity of birds at Hollister Hills. Abundance is not always a good predictor of habitat quality, however, so further research is needed to understand the demographic consequences of OHV use on bird species.