Riparian Bird Nest Monitoring and Cowbird Management, Coachella Valley

Guided by the results of baseline surveys conducted in 2002-2004 by the Center for Conservation Biology, and resurveys conducted in 2014 by the San Diego Natural History Museum, our team began implementation of management recommendations for five bird species identified as targets for conservation and one species identified as a management concern by the Coachella Valley Multiple Species Habitat Conservation Plan (CVMSHCP). These include sensitive species Willow Flycatcher, Least Bell’s Vireo, Yellow Warbler, Yellow-breasted Chat, and Summer Tanager; and brood parasite Brown-headed Cowbird.

Due to strong declines in these sensitive riparian species’ numbers and high abundance of cowbirds and parasitism rates documented by the Museum in 2014, the team initiated cowbird trapping at two sites in 2017.

To assess the effectiveness of this management action, a team of experienced ornithologists from the Museum concurrently monitored riparian birds at these two sites and at four other sites without cowbird trapping. Survey protocols followed those established during the 2002-2004 baseline surveys, with the addition of point counts for all riparian birds, rapid habitat assessments, and nest monitoring, during which cowbird eggs and chicks were removed when found, and target species’ territory locations, cowbird activity, and nest location, height, substrate, and status were documented.

In 2017, the team trapped a total of 84 cowbirds and banded and released 23 males to determine recapture rates. Using the 2017 survey and monitoring data, researchers estimated density, nest parasitism rates, and reproductive success for each target species, which will be used as a baseline to assess the effectiveness of the ongoing cowbird management efforts.

For each site, BioServices staff identified additional specific management actions that could help to maintain or increase populations of the five target riparian species and maintain or improve the quality of those species’ habitats over the long-term.