Project Manager, San Clemente Bell's Sparrow Monitoring Institute for Wildlife Studies San Diego, California, United States
Background/Question/Methods:
San Clemente Bell’s sparrows (Artemisiospiza belli clementeae) are endemic to San Clemente Island, California (SCI), which is owned and administered by the U.S. Navy. Loss of habitat by feral grazers during the 20th century led to the US Fish and Wildlife Service listing the San Clemente Bell’s sparrow as a Threatened Species in 1977. After removal of feral browsers by 1993, regrowth of native vegetation developed a greater variety and distribution of shrub communities across the island, with subsequent expansion of sparrows into these recovering habitats. However, fires from military training occur in some areas reoccupied by sparrows, and at larger scales and greater frequency than where sparrows were previously distributed. As a result, fire may present a greater threat to the persistence of the sparrow population than it did prior to recovery.
Surveys for Bell’s sparrow territories on SCI from 2013 – 2020 included randomized sampling stratified by habitat type to quantify presence and number of territories. We combined these data with fire history from 1985 – 2019, and modeled sparrow presence and density with and without fire history for a post-hoc analysis of fire effects on San Clemente Bell's sparrow distribution.
Results/Conclusions:
After accounting for habitat and year of survey, analyses showed that fires occurring within the previous 40 years reduced both Bell’s sparrow presence and density, and years since last fire increased the probability of sparrow presence as well as density. Our data only included current habitat types, and we do not have data representing the long-term trajectory of vegetation response to fire on SCI. We therefore are unable to compare the post-fire development of vegetation communities and how those relate to sparrow densities.
Despite the apparent effect of fire on Bell's sparrows, the population has expanded where the U.S. Fish and Wildlife Service recently proposed delisting. However, because Bell's sparrow densities tend to be highest in shrub habitats, fire management strategies that target these areas to reduce incidence, spread, frequency, and intensity of fires will assist in conserving and sustaining the population of San Clemente Bell's sparrows.
