An endangered snake thrives in a highly urbanized environment

The endangered San Francisco garter snake Thamnophis sirtalis tetrataenia occurs in only 2 counties on the densely populated San Francisco Peninsula, California, USA. Due to its limited geographic range and destruction of populations by the rapid pace of urban development in the 1950s and 1960s, T. s. tetrataenia was the only snake included in the inaugural US Endangered Species Act. Several large areas preserved as public parks, utility lands, or private trusts support remnant populations that are the focus of recovery and conservation efforts. To assist in assessment of status and trend for this subspecies, we fit Huggins’ closed capture models in RMark to mark-recapture data collected in 2007 and 2013 to estimate population size of an isolated population on a small (72.8 ha) property surrounded by residential development and transportation infrastructure. Our best supported models indicate a population of 1763 individuals (95% CI: 1302-2446) in 2007 and 1761 (95% CI: 1211-2639) in 2013. In addition, total captures of an important prey species increased 2 orders of magnitude from 829 in 2007 to 17180 in 2013. These findings highlight the potential for well-managed but small habitat units (‘the good’), to compliment vast natural areas (‘the ideal’) in recovery and conservation strategies for threatened and endangered species that can be supported by a small home range.