Assessment of Chukar and Gray Partridge Populations - Idaho Power

Hells Canyon Chukar and Gray Partridge Report, Ratti and Giudice 34relationship between density and index values. Early morning call counts for gray partridge maybe an appropriate method of monitoring gray partridge in Hells Canyon.4.10. Limiting Factors4.10.1. Weather4.10.1.1. Chukar. Environmental conditions, which govern weather and foodsupply, play an important part in regulating nesting and hatching success and, subsequently,annual population density of chukars (Christensen 1996). Furthermore, given that basic habitatsof chukar are found in arid or semi-arid regions, the primary factor influencing reproductivesuccess and annual production is the amount of precipitation received during key periods of theyear (e.g., Walter 2000). The effective precipitation in any given range largely determines thecomposition, abundance, and condition of essential food plants, which in turn play a major rolein influencing annual production (Christensen 1958, 1970). In Nevada, chukar populationsduring 1951-69 typically exhibited a “boom or bust” pattern that was correlated with droughtconditions and the subsequent lack of food (Christensen 1970). According to Christensen(1970:45), “when a population bottoms out, it seems to require a minimum of three goodproduction years, back to back, to bring the population to a peak again. Such a sequence doesnot usually occur and the population may drift along at a mediocre level for several years.”Although no quantitative data are available, comparisons of production data with timing ofprecipitation during nesting and hatching suggest that unseasonable rains and snows cansignificantly lower nest success and chick survival (Christensen 1970). Likewise, heavysnowfall in combination with cold temperatures can result in substantial overwinter mortality,especially in areas where elevational movements are restricted (Christensen 1952b). Forexample, Galbreath and Moreland (1953) estimated 65-75% mortality due to severe winterconditions in Washington during in 1949-50. However, heavy losses from winter storms areusually erratic in nature and populations often recover relatively quickly through immigrationand the high reproductive potential of survivors (Galbreath and Moreland 1953, Christensen1970).4.10.1.2. Gray Partridge. Weather has been shown to have strong effects onrecruitment and overwinter mortality in Wisconsin (Church 1980), New York (Church andPorter 1990a), Montana (Weigand 1980), and Great Britain (Potts 1986). Severe winter weather,especially deep or crusted snow, has been correlated with increased mortality (Potts 1986, Panek1990). In contrast, weather variables explained little of the annual variation in population changeon the Palouse Prairie of eastern Washington during 1940-92, but this area is characterized byconsistently dry summers and moderate winters (Rotella et al. 1996). Nevertheless, brief intensestorms or depth and hardness of snow pack could occasionally affect the Palouse Prairiepopulation. There have been no studies on effects of weather on populations inhabiting HellsCanyon, but effects of drought and spring storms are probably similar to that described forchukars (see above). However, gray partridge are able to survive extreme winter temperaturesby roosting in tight groups and in deep, soft snow, and they can burrow through about 1 m of softsnow to find food (Carroll 1993). Thus, gray partridge may not be as vulnerable to severe winterweather as chukars.