Effects of land use on riparian birds in a semiarid region

We investigated the influence of landscape characteristics on avian species occupancy in riparian forests embedded in a matrix of urban and agricultural land use in a semiarid region of the Southwestern US. We conducted bird and vegetation (local-scale characteristics) surveys within 196 50-m radius sample points in 10 riparian forests in southern California. We quantified landscape composition within a 500 m-radius surrounding each point. For each species we developed 8 single-season occupancy models using principal components summarizing local- and landscape-scale characteristics and a spatial autocovariate as covariates. Of 21 species analyzed, occupancy by 11 was associated with landscape characteristics, by 6 with local vegetation characteristics, by 3 with both local and landscape characteristics, and by 1 with none. Five species positively responded to surrounding urban development (2 negative), whereas 4 negatively responded to agricultural land (1 positive). The amount of riparian forests had a strong positive effect on the occurrence of riparian obligates. Our results emphasize the importance of landscape characteristics on species occupancy patterns in riparian systems although relationships were also species-specific. Our results imply a positive effect of urbanization compared to agricultural land uses in this region, most likely due to enhanced vegetation development.