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Survival of Greater Sage‐Grouse Chicks and Broods in the Northern Great Basin
Author(s) -
GREGG MICHAEL A.,
CRAWFORD JOHN A.
Publication year - 2009
Publication title -
the journal of wildlife management
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.94
H-Index - 111
eISSN - 1937-2817
pISSN - 0022-541X
DOI - 10.2193/2007-410
Subject(s) - brood , biology , forb , lepidoptera genitalia , ecology , habitat , population , zoology , demography , grassland , sociology
ABSTRACT Reduced annual recruitment because of poor habitat quality has been implicated as one of the causative factors in the range‐wide decline of sage‐grouse ( Centrocercus urophasianus ) populations since the 1950s. Because chick and brood survival are directly linked to annual recruitment and may be the primary factors that limit sage‐grouse population growth, we estimated 28‐day survival rates of radiomarked chicks and broods from 2000 to 2003. We examined relationships between survival and several habitat variables measured at brood sites, including food availability (insects and forbs); horizontal cover of sagebrush, grasses, and forbs; and vertical cover of sagebrush and grass. We monitored 506 radiomarked chicks from 94 broods; chick survival was 0.392 (SE = 0.024). We found evidence that both food and cover variables were positively associated with chick survival, including Lepidoptera availability, slender phlox ( Phlox gracilis ) frequency, total forb cover, and grass cover. The effect of total grass cover on chick survival was dependent on the proportion of short grass. The hazard of an individual chick's death decreased 8.6% (95% CI = −1.0 to 18.3) for each percentage point increase in total grass cover when the proportion of short grass was >70%. Survival of 83 radiomarked broods was 0.673 (SE = 0.055). Lepidoptera availability and slender phlox frequency were the only habitat variables related to brood survival. Risk of total brood loss decreased by 11.8% (95% CI = 1.2–22.5) for each additional Lepidoptera individual and 2.7% (95% CI = −0.4 to 5.8) for each percentage point increase in the frequency of slender phlox found at brood sites. Model selection results revealed that temporal differences in brood survival were associated with variation in the availability of Lepidoptera and slender phlox. Years with high brood survival corresponded with years of high Lepidoptera availability and high slender phlox frequency. These foods likely provided high‐quality nutrition for chicks during early growth and development and enhanced survival. Habitat management that promotes Lepidoptera and slender phlox abundance during May and June (i.e., early brood rearing) should have a positive effect on chick and brood survival in the short term and potentially increase annual recruitment.