are alkaline and support several species of phyllopod shrimp. Plants 720 different species of plants are found in the Sandhills. Most are native, with only 7% exotics — half the percentage of most other prairie systems. Most of the "exotics" are invasive species and considered noxious weeds and must be destroyed by landowners. The blowout penstemon (Penstemon haydenii) is an endangered species, found only in the Sandhills and in similar environments in central Wyoming. The blowout penstemon stabilizes the soil where wind erosion exposes the bare sand and creates a blowout, but is choked out when other species begin to recolonize. Grazing and land management practices used by Sandhills ranchers have reduced natural erosion, thus destroying some of the plant's habitat. Many of the plants of the Sandhills are sand-tolerant species from short-grass, mixed-grass, and tallgrass prairies; plants from all three of these can be found within the ecosystem. These plants have helped to stabilize the sand dunes, creating an ecosystem beneficial for other plants and animals. Better land management and grazing practices by the ranchers of the region have led to less erosion over time, which has kept the natural landscape of the area mostly intact. Insects Many species of insect are found in the Sandhills, including dragonflies, grasshoppers and mosquitos. There are also many types of spiders. Due to the warm stagnant nature of both alkaline and freshwater lakes throughout the region, coupled with the wetland marsh areas, mosquito populations increase during the summer months. Birds The Sandhills are part of the Central Flyway for many species of migratory birds, and the region's many bodies of water give them places to rest. The ponds and lakes of the region are lay-over points for migratory cranes (particularly Sandhill cranes), geese, and many species of ducks. Species found year-round include the western meadowlark, the state bird of Nebraska. Conservation efforts and protection Valentine National Wildlife Refuge, located about 20 miles (32 km) south of Valentine, encompasses . Crescent Lake National Wildlife Refuge in the central Panhandle covers . The Nature conservancy's Niobrara Valley Preserve in Cherry, Brown, and Keya Paha counties covers 60,000 acres (202 km2) and includes a stretch of the river. Fort Niobrara National Wildlife Refuge near Valentine covers 19,000 acres (77 km2). Partnering in the effort to conserve the Sandhills are the Institute of Agriculture and Natural Resources, West Central Research and Extension Station, the Nature Conservancy