Assessment of Chukar and Gray Partridge Populations - Idaho Power

Hells Canyon Chukar and Gray Partridge Report, Ratti and Giudice 38Salmon River suggested that relative use of star thistle was lower than use of other habitats in1993-95; however, weather may explain more of the annual variation in chukar numbers thanrange expansion of star thistle, especially considering data from 1997 and 1999 (i.e., where 23and 45% of chukar observations were in star thistle, respectively) (C. Johnson, Bureau of LandManagement, Cottonwood Resource Area, ID, personal communication).Medusahead, another introduced annual, is extremely competitive and can out competecheatgrass in degraded grasslands (Hironaka et al. 1983, Franklin and Dyrness 1973). Westernrangelands infested with medusahead have suffered 40-75% reductions in grazing capacity(Whitson et al. 1996:497). Chukars readily ingest the caryopses of both medusahead andcheatgrass, but Savage et al. (1969) reported that captive birds fed downy brome (Bromustectorum) were in better condition than those fed medusahead. Thus, expansion of yellow-starthistle and medusahead and the subsequent decline in cheatgrass may pose a long-term threat insome areas currently inhabited by chukars (Walter 2000). However, more and better data areneeded to adequately evaluate the relative importance of habitat degradation (via yellow-starthistle and medusahead) and weather on chukar populations in the Intermountain West.4.10.6.2. Gray Partridge. Most gray partridge populations are closely associatedwith agricultural ecosystems; thus, they are affected by agricultural practices (Carroll 1993). InEurope, agricultural activities, including removal of hedgerow nesting cover, increased use ofpesticides, and irrigation activities in cereal crops used for nesting, have negatively affected graypartridge populations (Potts 1980, 1986; Rands 1986, Birkan et al. 1990). Detailed studies inGreat Britain indicated that nest success was density dependent (a function of habitat availabilityand predator levels), while chick mortality, influenced by pesticide use and abundance ofinvertebrates during summers, was density independent (Potts 1986:182-186). In NorthAmerica, much less is known about impacts of different farming techniques on gray partridge(Carroll 1993). However, availability of permanent nesting cover has been reported to limitpopulations in North America (Hupp et al. 1980, Church 1984, Carroll et al. 1990), including thePalouse Prairie (Knott et al. 1943, Poelker and Buss 1972, Mendel 1979, Rotella et al. 1996). Onthe other hand, increases in some agricultural activities may have benefited partridge populationson the Palouse Prairie; e.g., fall-planted wheat fields provide better nesting cover than springplantedwheat fields and may provide nesting habitat for a small portion of the population(Rotella et al. 1996). However, these factors may not be as important for gray partridgeinhabiting mountainous areas such as Hells Canyon. For example, given the extensive grasslandand shrub-steppe habitats in Hells Canyon, nesting cover may not be limiting, althoughquantitative data on habitat use are lacking. In general, effects from invasions of noxious weedson the gray partridge population inhabiting Hells Canyon are unknown.4.11. Conservation and Management4.11.1. ChukarThe principal human effect on chukar populations is hunting, which can becontrolled through proper regulation (Christensen 1996). Estimated harvest rates of mostpopulations are substantially below the maximum-allowable rate of 40% recommended byMolini (1976; also see 4.10.4 Hunting, above). Thus, most chukar populations are probably