Coastal California gnatcatcher, Polioptila californica (CAGN) numbers have decreased from historical levels due to multiple factors such as the loss of coastal sage scrub habitat, wildfires and invasive plants. However, our team documented a high number of nesting pairs at the University of California Irvine, San Joaquin Marsh, Orange County. We are currently studying the reproduction and dispersal of CAGN by color-banding juvenile birds and re-sighting them after dispersal. Our research will identify the San Joaquin Marsh Reserve, as a source or a sink for CAGN, as well as quantify regional nest survivorship, natal dispersal and inform adaptive management recommendations for local conservation and recovery. In the initial year of our study, 2023, we documented 10 CAGN pairs on breeding territories at the marsh and banded a total of 46 CAGN. In the spring of 2024, we will continue banding at the marsh and start a comprehensive re-sighting effort. The marsh is a managed and restored site and the results of our study will provide insights into long-term management of coastal sage scrub (CSS) for CAGN habitat. In addition, this study is a test of the core and linkage reserve design and will provide information about current dispersal movement.