Bird and Small Mammal 

 Populations in a Grazed 

 and Ungrazed Riparian 

 Habitat in Idaho 



Dean E. Medin 

 Warren P. Clary 



EVTRODUCTION 



Livestock grazing in riparian ecosystems has been a 

 recent focus of rangeland management in the Western 

 United States (Swanson 1988). Cattle prefer riparian 

 areas for the quality and variety of forage, for easy acces- 

 sibility, for shade, and for a generally reliable source of 

 water (Ames 1977; Gillen and others 1985; Martin 1979). 

 Riparian ecosystems are similarly important to wildlife. 

 Many species of wildlife are either directly dependent on 

 riparian habitats or utilize them more than other habitats 

 (Thomas and others 1979). 



Several studies have reported adverse effects of cattle 

 grazing on riparian vegetation, and recovery of vegetation 

 when grazing is modified, reduced, or eliminated (Ames 

 1977; Knopf and Cannon 1982; Rickard and Cushing 

 1982; Taylor 1986; Winegar 1977). Recovery of riparian 

 vegetation following removal of livestock can be dramatic. 

 If habitat deterioration is not severe, herbaceous vegeta- 

 tion can increase significantly within several growing 

 seasons (Platts and Nelson 1984), and woody vegetation 

 may recover within 5 to 10 years (Rickard and Cushing 

 1982; Skovlin 1984). But severely deteriorated habitats 

 may require long recovery times, perhaps decades (Knopf 

 and Cannon 1982) or more (Platts and Raleigh 1984). 



Exclosures, natural areas, and other areas that have 

 received minimal use by livestock are often used as refer- 

 ence areas on rangelands (Kauffman and Krueger 1984; 

 Ohmart and Anderson 1986). Livestock exclosures pro- 

 vide opportunities to study vegetation and associated 

 wildlife communities on ungrazed as compared to grazed 

 habitats. This report compares breeding bird and small 

 mammal populations between a riparian habitat season- 

 ally grazed by cattle and a comparable adjacent riparian 

 area protected from grazing for the previous 14 years by 

 a fenced exclosure. The 122-ha exclosure, constructed in 

 late 1975, is on Summit Creek in east-central Idaho. Bird 

 populations were assessed in the spring of 1989. Small 

 mammal populations were compared by removal trapping 

 during late summer of both 1988 and 1989. 



Common and scientific names of birds and small mam- 

 mals referred to in this paper are listed in the appendix. 



STUDY AREA 



The Summit Creek study area is 41 km north of Mackay 

 in Custer County, ID, at an elevation of about 1,975 m. 

 It is near the southern boundary of the Northern Rocky 

 Mountains physiographic province (Fenneman 1931) in the 

 Little Lost River drainage. Summit Creek originates fi-om 

 springs and flows through a gently sloping, basinlike val- 

 ley bounded on the east by the Lemhi Range and on the 

 west by the Lost River Range. The mountain ranges are 

 rugged and serrated and chiefly composed of limestone, 

 dolomite, quartzite, shale, and schist (Kirkham 1927). 



Regional climate is semiarid. Average annual precip- 

 itation at Mackay (elevation 1,797 m) is 247 mm, with 

 peaks in May and June. The growing season is short, 

 averaging less than 100 days at Mackay (USDC NOAA 



1982) . Microrelief in many parts of the riparian area is 

 hummocky, with soils high in total salts (USDA SCS 

 1987). The riparian zone seldom exceeds 50 to 100 m 

 in width. 



Several vegetation community types were identified in 

 the riparian area and adjoining upland. For our study, 

 we consolidated the community types into three general 

 categories: sagebrush {Artemisia spp.)/upland, mat muhly 

 {Muhlenbergia richardsonisyhnmmock, and mesic herba- 

 ceous. The sagebrush/upland type occupies the gentle 

 slopes and terraces adjoining the riparian zone. The other 

 two types — mat muhly/hummock and mesic herbaceous — 

 were considered components of the riparian habitat. 



Upland vegetation on the site is shrub-steppe (West 



1983) . The dominant shrubs are low sagebrush (A arhus- 

 cula) and threetip sagebrush (A tripartita), with occa- 

 sional individuals of green rabbitbrush {Chrysothamnus 

 viscidiflorus), gray horsebrush {Tetradymia canescens), 

 and big sagebrush (A tridentata). The herbaceous stra- 

 tum commonly includes Sandberg's bluegrass (Poa sand- 

 hergii), bluebunch wheatgrass (Agropyron spicatum), aster 

 {Aster spp.), and long-leaf phlox {Phlox longifolia). The 

 hummocky areas are dominated by herbaceous species, 

 most notably mat muhly and thick-spiked wheat-grass 



(A dasystachyum), and including Kentucky bluegrass 

 {P. pratensis), tufted hairgrass {Deschampsia cespitosa). 



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