1 / 30

Estimating Greater Sage-grouse Juvenile Survival in Utah

This study conducted by Utah State University aims to estimate the survival of juvenile Greater Sage-grouse in Utah. The study examines various factors such as predation, hen behavior, vegetation, and arthropod population. Results indicate that predation is a major cause of mortality, but overall survival is good. The study also suggests that brood-mixing and arthropods may play a role in chick survival.

williamkay
Download Presentation

Estimating Greater Sage-grouse Juvenile Survival in Utah

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Estimating Greater Sage-grouse Juvenile Survival in Utah Utah State University David Dahlgren Terry Messmer David Koons

  2. Introduction • Info Need

  3. Study Area • Parker Mountain

  4. Methods

  5. Methods – Burkepile et al. 2002

  6. Methods • Hen Behavior

  7. Methods • Monitoring

  8. Methods • Veg and Arthropod Sampling

  9. Brood Mixing

  10. Methods • Cause of mortality • Handling • Exposure • Predation • Avian/Mammalian • Unknown

  11. Methods • Modeling • Manly and Schmutz 2001 - JWM • Maximum Likelihood Estimation (Version of the Mayfield Estimator) • Heterogeneity - D

  12. Methods • Modeling Survival • First • Age Structure (weeks 1 to 6) • Used to assess covariates • AIC • Second • Assess covariates • Temporal • Brood hen characteristics • Vegetation data • Arthropod data

  13. Methods • Modeling Survival • Assumptions • Brood-mixing and right censoring • Missing chicks • Brood-mixing and missing chicks

  14. Methods • Modeling Survival • First Covariates • Year • Brood Type • Hen Behavior (restricted data set) • Hen Age (restricted data set) • Hatch Date

  15. Methods • Modeling Survival • Second – Vegetation Covariates (restricted data set) • Shrub cover and height • Grass cover and height • Forb cover and height • Third – Arthropod Covariates (2006, restricted data set) • Hymenoptera (ants separate), Coleoptera, Lepidoptera, Orthoptera, miscellaneous, and total arthropods

  16. Results • Sample sizes • Total • 2005 n = 89 chicks in 21 broods (mean = 4.24) • 2006 n = 61 chicks in 21 broods (mean = 2.91) • Handling Death (2.6%) • 2005 n = 3 • 2006 n = 1 • Excluded from the survival analysis

  17. Results • Sample Sizes • Chick mass • Mean = 29.5g (SE = 0.16) • Transmitter averaged 5.1% (SE = 0.0003) of chick weight • Hen Behavior • 43% Very protective (18/42) • 38% Moderately protective (16/42) • 19% Non-protective (8/42)

  18. Results • Sample Sizes • Brood Mixing • 21% of marked chicks (31/146) • 43% of marked broods (18/42) • 45% of mixing events involved >1 chick (9/20) • Occurred weeks 1 to 6 • 70% (14/20) in weeks 2 and 3 • Radio-marked hen mortality (n = 2)

  19. Results • Sample Sizes • Chick Mortality • n = 44 documented deaths • n = 26 missing (assumed depredated) • n = 6 exposure • Predation 91% (64/70) • Unknown 75% (48/64) • Mammalian 12.5% (8/64) • Avian 12.5% (8/64)

  20. Results First – Age parameterization Second – Temporal and hen characteristics : AIC difference between a model (i.e., model i) and the best performing model (i.e., model with the lowest AIC among the set of models examined). wi: Akaike model weight. * The best model of age = (week1) + (week2) + (week3) + (week4) + (weeks5-6)

  21. Results First – Age parameterization

  22. Results Second – Temporal and hen characteristics

  23. Results Mean Survival to 42 days = 0.41 (SE =0.046) Chick Survival in Regular broods = 0.38 Chick Survival in Mixed broods = 0.61

  24. Results • Heterogeneity (D) • Chicks/brood = 3.5 • For best model • D = 1.10 (SE = 0.22)

  25. Results • Vegetation Covariates • Null Model is best

  26. Results • Arthropod Covariates • Entire 42 days • Ant model

  27. Results • Arthropod Covariates • Early brood-rearing (day 1-21) • Orthoptera (grasshopper) model • Estimates not significant

  28. Take Home • Predation major cause of chick mortality • However, survival was good (mean = 0.41) • Our data suggested low dependence among brood mates for sage-grouse chicks • Brood-mixing may be important to survival, needs further investigation • There is evidence that Arthropods (especially Orthoptera) may aid chick survival, needs further investigation (> sample size)

  29. Thanks People • Technicians • Nathan Burkepile • Jack Connelly • Volunteers PARM • USU Extension • Parker Mtn. Grazing Association • Jack H. Berryman Institute • UDWR • USFS • BLM • NRCS • SITLA • Farm Bureau • County Commissioners

  30. Any Questions?

More Related