OCR Text |
Show in nesting colonies around the lake. Eared grebes also utilize this habitat type, although they are not necessarily nesting along with the species previously mentioned. The populations of these species are substantial. As lake level fluctuates, the location of the bulrush- open water interface constantly changes. The dynamic of the GSL shoreline helps to maintain pioneering stages in emergent vegetation types which are important in developing habitat edge and vegetation density. It allows for periodic open mudflats and playas important for certain bird species and breeding sites for invertebrates. Changing habitats are the key to wildlife diversity and abundance in GSL ecosystems. Woody Vegetation There is another group of species which utilize a relatively rare habitat type around the lake. This is woody vegetation in the form of trees and large shrubs. These are usually found along the waterways entering the marshes or planted along dikes and uplands by wildlife managers. All of the trees below lake elevation 4212 feet were killed by salt water and/ or flooding during the mid- 1980s. Some of the dead trees still persist and new trees have been planted or have naturally re- established. These woody plants are excellent nesting sites for such species as Great Blue herons. Snowy egrets, Black- crowned night herons and Double- crested cormorants. Other species such as raptors utilize these trees as well. Pelagic Areas Red- necked phalaropes feed on brine shrimp in the open waters of the lake. Gulls are observed there as well. They feed upon dead brine shrimp and brine flies which collect in windrows on open water. Waterfowl GSL is located on the eastern edge of the Pacific Flyway. These corridors are the major routes that populations of birds utilize when migrating north and south. These flyways were defined for administrative considerations primarily, not biological, and are utilized in the analysis of bird banding data. It was discovered that birds typically, although not exclusively, migrate in north- south corridors. Many species of waterfowl have been documented on and around GSL. Over 75 percent of the western population of Tundra swans utilize the lake as a stopover and foraging area during their migration. As many as 60,000 birds have been observed at peak times. They utilize the large lake areas within state WMA and BRMBR. Sago pondweed grows in these units and is a preferred forage. Trumpeter swans also occasionally inhabit the area. USFWS and DWR have been transplanting Trumpeter swans here from areas where populations have exceeded the food source as a means to broaden their wintering range across the west. Breeding A number of breeding ducks use marshes around the lake. The nesting habitat types used range from dry upland areas to emergent marshes. The open or pelagic areas of the lake are very important to many birds. These areas are primarily used for either foraging or resting. Eared grebes and 76 |