Salt Marsh Harvest Mouse, the Tiniest Endangered Species

Most inhabitants of the Bay Area are aware of threatened species such as the sea otter and harbor porpoise, or even the endangered California clapper rail, but there’s a mammal that’s completely unique to the Bay Area and so tiny most people have never even seen one.This mammal, among the smallest rodents in the U.S., lives only here in the Bay in a very specific habitat, and can be credited with much of the tidal marsh restoration happening now.

In 1970, thanks to the work of Dr. Howard Shellhammer, the Environmental Protection Agency listed the salt marsh harvest mouse as endangered, and kick-started the explosion of San Francisco Bay conservation efforts. The endangered status of the salt marsh harvest mouse halted plans for development, agriculture, and industrialization of natural marsh habitat. US EPA - Endangered Species Facts  - Salt Marsh Harvest Mouse

A salt marsh harvest mouse is about the size of one’s thumb, largely nocturnal, and lives among the reddish pickle weed in the low tidal marsh—an area frequently subject to tidal inundation. Salt marsh harvest mice are adapted to live in this challenging environment, as they can swim short distances and consume food and water with a high salt content.

During high tides and peak flooding by storms, salt marsh harvest mice escape into the upland marsh for protection. It is this safe-haven habitat that has been greatly diminished and is of most concern for the survival of these tiny mammals. Without this high tide refugia, or proper corridors permitting travel to them, salt marsh harvest mice are subject to drowning and predation. The threat of sea level rise makes this an even greater concern

Although some of the habitat of the salt marsh harvest mouse is protected around the Bay, the continuing threats from pollution, poor water quality, invasive species, and habitat fragmentation are driving the population into further decline. Under the umbrella of the United States Fish and Wildlife Service Tidal Marsh Recovery Plan, Save The Bay is working to prevent the loss of the salt marsh harvest mouse by preserving and restoring vital marshland habitat. Harvest mouse habitat is also habitat for hundreds of other species. That’s why Save The Bay works to prevent further filling of Bay tidal marsh, combat pollution, and restore the vital marsh habitat that the salt marsh harvest mice use during winter high tides and storms.

This winter we are planting 45,000 plants to provide suitable marsh habitat for this endangered species. Volunteer with us this season to plant suitable refuge for these unique, adorable rodents!