Survival of Golden Eagles Aquila chrysaetos in Denali National Park

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Survival of Golden Eagles (Aquila chrysaetos) in
Denali National Park

• WLF 410
• Neil Lehner
• Chad Bieberich
• Judy Zacharius
• Carl Roberts

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Introduction

• Life History of Golden Eagles
• Life span
• Range
• Reproduction
• Migration

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Introduction (2)

• Data Carol McIntyre
• 1997-1999 Denali National Park
• 41 Nestlings tracked for 11 months
• Satellite and VHF transmitters

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Introduction (3)

• Migration of Alaskan Golden Eagles
• Divided into 5 time periods
• 1st Autumn Migration (9 weeks)
• Early Winter (9 weeks)
• Late Winter (8 weeks)
• Spring Migration (13 weeks)
• First Summer (9 weeks)

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Introduction (4)

• Information of Interest (covariates)
• Sex
• Size of the brood
• Hatch date
• Productivity of nesting territories
• Length of post-fledging dependence
• -first record of leaving nest and not returning

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Goals of the Project

• Determine if survival differs among time periods
• Determine how the covariates affect survival
• Determine how long these effects persist

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What We Found

• Model without time-specificity was highest
  ranked.
• Productivity had the strongest influence on
  survival among all covariates
• All covariates were categorized as having either
  acute, chronic or uncertain effects on survival
  (more later).

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Methods

• Known Fate Analysis
• Time Specific models
• Survival varies with each time period S(t)
• Migration / Non-migration S(migration)
• No time Variance S(.)

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Methods (2)

• Overall effects of individual covariates
• Length of these effects
• Chronic (lasting)
• Modeled effects over all of the 5 time periods
• S(tsex) chronic
• Acute (short)
• Modeled effects only over the first time period
• S(tsex) acute

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Methods (3)

• Selecting among the models
• AICc Value rank
• Delta AICc value
• Real and beta estimates
• Confidence Intervals
• Standard Error

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Model Results

• Table 1. shows model selection criteria and
  models ranked by AICc values.

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Time Specific Model Results

• Table 3. shows the ranking of time specific
  models using AICc values. Survival estimates are
  shown with upper and lower confidence intervals

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Fig. 1. Confidence intervals on the survival
estimates from the model S(t). The black bars are
bounded by the upper and lower confidence limits.
Time periods are in chronological order starting
with first autumn migration. Large overlap in the
confidence intervals is readily apparent between
the survival estimates.
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Covariate Results

• Table 2. shows the ranking of covariates based on
  AICc values and beta estimates used for overall
  effects on survival.

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Discussion

• Determine if survival differs among the 5 time
  periods
• S(.) ranked highest with small confidence
  intervals
• Estimates for S(t) were not constant

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Discussion (2)

• How the covariates effect survival
• How long the effects of the covariates last on
  survival
• Acute vs. Chronic effects

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Survival vs. Productivity

• Figure 1. shows the acute and chronic effects of
  historical nest site production on survival.

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Survival vs. Hatch Date

• Figure 2. shows the acute and chronic effects of
  hatch date on survival.

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Survival vs. Sex

• Figure 3. shows the acute and chronic effects of
  sex on survival.

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Survival vs. Brood Size

• Figure 4. shows the acute and chronic effects of
  brood size on survival.

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Survival vs. Length of Dependence

• Figure 5. shows the acute and chronic effects of
  length of dependence on survival.

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Summary

• Most confidence in a model where survival is held
  constant over time.
• Among all of the covariates, productivity of the
  nesting territory is most strongly related to
  survival.
• Covariates were categorized as having either
  acute, chronic or uncertain effects on survival.
  We need more precision in our estimates to be
  more confident in these relationships.

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Acknowledgements

• Our thanks to
• Carol McIntyre for allowing us to use her data
  for this project
• Mark Lindberg for his guidance and knowledge

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Questions?