The purpose of this study is to gather genetic data from museum samples collected in the early 1900s to compare levels of genetic diversity and population structure to present day estimates. From this analysis, USGS hopes to determine whether there has been an increase in population genetic differentiation and a loss of genetic diversity in Southern California Cactus Wrens over the past century, and to quantify these changes. Results will help inform potential management actions such as choosing source populations for re-establishment and augmentation. This project will consist of the following objectives:1) Develop protocols for DNA extraction and amplification of historical museum samples for microsatellite loci; 2) Travel to museums in California to retrieve tissue from relevant museum specimens; 3) Genotype samples, analyze patterns of genetic differentiation and diversity, and prepare a report comparing past to present population genetic structure.