Survival of Columbian sharp‐tailed grouse chicks and juveniles in northwestern Colorado

Abstract

AbstractChick and juvenile survival are important vital rates for population monitoring and making sound management decisions. These demographics are poorly understood in Columbian sharp‐tailed grouse (Tympanuchus phasianellus columbianus) and survival estimation in the first 2 weeks is particularly challenging to assess. In 2015–2017, we captured 1,219 chicks (1–7 days old) from 156 broods. We marked 625 chicks with radio‐transmitters to monitor their survival and recaptured them to replace the radio‐transmitter from 18–30 days old. Overall survival of chicks and juveniles for the brood‐rearing season (initial capture–31 Aug) was 0.30 ± 0.02 (SE; 95% CI = 0.26, 0.35, n = 746) using the Kaplan‐Meier product‐limit estimator. We used Cox proportional hazards regression to model survival and for chicks entering the study at 2–4 days old, survival to 21 days old was 0.59 ± 0.03 (95% CI = 0.53, 0.65, n = 529) and increasing chick mass had a positive effect on chick survival probability, with a 6.0% decrease in mortality risk for each additional gram of mass at initial capture. Juvenile survival was 0.51 ± 0.04 (95% CI = 0.43, 0.60, n = 294) and differed by study site. Of our 4 study sites, the 2 western sites (West Axial, Iles Dome) had 65–80% greater hazard compared to the 2 more eastern sites (Routt, Trapper). Juvenile survival was also influenced by hatch date, with a 3.0% greater hazard for each day later in the nesting season that a nest hatched. Because chick survival is positively influenced by greater mass at capture and juvenile survival was positively affected by earlier hatching dates of broods, management actions should focus on improving the habitat surrounding lek sites to increase the success of initial nests and to provide high quality (increased levels of calcium, phosphorus, and protein) and quantity forage to nesting females and chicks to increase survival and population stability. Additionally, given that lower mass increases the hazard for chick survival, researchers planning to mark chicks should not mark individuals <11 g when using a 0.55‐g radio‐transmitter. Radio‐transmitters for chicks should not exceed 5.0% of the chicks' body mass at the time of marking.