Ecology of greater sage-grouse in the Dakotas

Greater sage-grouse (Centrocercus urophasianus) populations and the sagebrush (Artemisia spp.) communities that they rely on have dramatically declined from historic levels. This dissertation addresses factors that influence sage-grouse survival, winter habitat use, seasonal movements, and brood breakup based on research conducted from 2005-2007 in southwest North Dakota and from 2006-2008 in northwest South Dakota. Identifying critical periods of survival in sage-grouse during their annual life-cycle is important to support biologically based management actions. I evaluated factors influencing survival of 219 breeding-age (≥1 year of age) and juvenile (≥10 weeks of age) radio-marked sage-grouse using known-fate models in program MARK. I evaluated factors influencing annual (1 Mar -- 28 Feb) and seasonal survival during five periods that reflected the chronology of their life-cycle in this region including: breeding (1 March -- 15 April), nesting (16 April -- 15 June), early brood-rearing (16 June -- 15 July), late brood-rearing (16 July -- 31 October), and winter (1 November -- 28 February). Survival was generally high except during the late-brood rearing period when there was high mortality (>50%) related to West Nile outbreaks and predation. Low recruitment compounded by the negative effects of West Nile virus may limit the sustainability of the low density sage-grouse population in this region. I also evaluated factors influencing sage-grouse winter habitat use in North Dakota 2005-06 and 2006-07 and in South Dakota 2006-07 and 2007-08. I used conditional logistic regression to test competing models of winter habitat use at used (n = 340) and 250 (n = 340) and 500 m (n = 340) dependent random sites from 124 radio-marked sage-grouse. Percent sagebrush canopy cover was the primary factor influencing winter habitat use in this region. Habitat used by sage-grouse was characterized by 7.6% higher sagebrush canopy cover than at random sites. My results indicated that sagebrush canopy cover (15%) and sagebrush height (20 cm) meet their winter habitat requirements during mild winters. Management should focus on avoiding additional loss of sagebrush habitat, identifying areas of critical winter habitat, and implementing management actions based on causal mechanisms (e.g., soil moisture, precipitation) that affect sagebrush community structure in this region. Movement behavior of sage-grouse varies by region and may be affected by the configuration of seasonal habitats. I documented movements of sage-grouse in the Dakotas during all aspects of their life-cycle to evaluate the timing and frequency of sage-grouse migration, estimating migratory an d non-migratory sage-grouse survival, evaluating seasonal distribution and core seasonal ranges, and estimating the timing and distance of natal dispersal by juvenile sage-grouse. Timing of spring migration coincided with abandonment of leks by males and age of chicks (i.e., 3-4 weeks) for females. Timing of migration from summer to winter and winter to breeding ranges was less obvious, as movements were gradual and occurred over several months. Evidence of migration in this population indicates that highly interspersed seasonal habitats may not completely regulate migration. Mild winter weather, tradition, and behavioral plasticity may have influenced migration rate. Because of recent population declines, management of sage-grouse in this region may need to focus on maintaining or increasing population sizes to prevent loss of gene flow because sage-grouse rarely migrated outside the study areas and emigration rates appear to be low. I captured and relocated 29 radio-marked broods of sage-grouse to identify movement patterns, timing, and juvenile survival associated with brood breakup during 2005-2006 in North Dakota and 2006-2007 in South Dakota, respectively. Median date of brood breakup was 4 October (range = 17 Jul -- 8 Nov) when juveniles reached a median age of 134 days (range = 38--173). Timing of brood breakup was independent of gender, juvenile age, brood female age, or study area. Brood breakup was usually initiated by the female and juveniles dispersed within days of the female abandoning the brood. Survival of juveniles from 10 weeks of age to 1 March was lower (P < 0.01) for orphaned juveniles (31.8 +/- 0.10%) compared to juveniles (72.2 +/- 0.11%) from broods that stayed with the female until brood breakup. Mortality to sage-grouse brood females before brood breakup appears to be additive to the survival of juveniles when population densities are low. (Abstract shortened by UMI.)...