Short-term riparian restoration success measured by territory density and reproductive success of three songbirds along the Trinity River, California

Water crises and endangered salmon are pressing environmental concerns influencing restoration decisions in the western United States. When instream restoration necessitates initial loss of riparian cover to restore floodplain function, a short-term goal to minimize harm to riparian-associated wildlife is a worthwhile benchmark. From 2012 to 2015, we examined short-term restoration success, as measured by territory characteristics and reproductive success in restored and reference sites, for 3 riparian bird species (Song Sparrow [Melospiza melodia], Yellow-breasted Chat [Icteria virens], and Yellow Warbler [Setophaga petechia]) along a 64 km stretch of the Trinity River, California. Territory size had the highest relative variable importance in sets of candidate models explaining territory density for all 3 species, and was inversely related to territory density for each. The effect of site type (i.e. restored vs. reference) in explaining territory density was least for Song Sparrow, greater for Yellow Warbler (for which density was 1.4 times greater on reference sites), and greatest for Yellow-breasted Chat (which were more than twice as dense on reference sites). While territory density and mean territory size were inversely related, we found no relationship between territory density or site type and mean productivity per nest, and nest success did not differ between restored and reference sites for any species. In combination, these results suggest that restoration has achieved short-term success as measured by reproductive success, but has not yet been fully successful in supporting similar territory densities as reference sites. In order to determine whether long-term restoration goals are fully achieved, future research should continue to measure density of the 3 focal species as vegetation on the replanted floodplains matures.