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Vernal Pools Vegetation Vernal pools are topographic depressions underlain by a hardpan or other impermeable soil layer. These depressions fill with water during winter, slowly dry out through spring, and become desiccated during summer. Vernal pools may be hydrologically isolated from one another or connected by shallow overflow swales. r Five vernal pools were mapped on the project site totaling approximately 1 acre (Figure 3). These pools support species characteristic of northern hardpan- and claypan- type pools. Dominant species identified during the late-summer survey period include popcorn flower, woolly marbles, Sacramento mesamint, common spike-rush, navarettia, spike-primrose, hyssop loosestrife, coyote-thistle, annual hairgrass, Mediterranean barley, annual ryegrass, cat's ear, doveweed, and soft chess. Species composition did not vary significantly between the five pools. Wildlife Although vernal pools are an ephemeral aquatic habitat,several aquatic invertebrate species have adapted to this regime and are able to survive dry summer conditions. The project site vernal pools were dry during the field surveys. Vernal pools are important breeding places for amphibians, such as western spadefoot toads, Pacific treefrogs, and tiger salamanders, which lay their eggs in the pools then return to uplands. Invertebrates, such _ as fairy shrimps, crawling water beetles, copepods, and tadpole shrimps, serve as food for amphibian larvae and for the many birds that overwinter or migrate through the Central Valley. In winter and spring,water birds, such as mallards,cinnamon teal, killdeer, and great- blue herons, probably use vernal pools for resting and foraging. Black phoebes, swallows, and bats feed on flying insects above water. Common and western terrestrial garter snakes, gopher snakes, and mammals, such as striped skunks and raccoons, prey on amphibian larvae and aquatic insects in vernal pools. SPECIAJrSTATUS SPECIES Special-status species are plants and animals legally protected under the state and federal Endangered Species Acts or other regulations and species considered sufficiently rare by the scientific community to qualify for such listing. Special-status species are defined for the purpose of this document to include species in the following categories: ■ plants and animals listed or proposed for listing as threatened or endangered under the federal Endangered Species Act (50 CFR 17.11 for listed animals; 50 16