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Population Limitation in Bicknell’s Thrush: a Female Problem? <ul><li>Chris Rimmer and Kent McFarland – VCE </li></ul><ul>...
Partners In Flight = North America Watch List IUCN Red List = Vulnerable ABC/Audubon WatchList = Red List Canada = Candida...
“ Differential mortality of females during the non-breeding season, resulting from effects of dominance, may thus also con...
n=4 n=4 n=10 n=3 n=5 n=7 Overall mean =  2.2 males : female n = number years Breeding Adult Sex Ratios Gaspe and Gosford d...
Recapture Probability for Mansfield and Stratton
n=5 nests n=5 nests Nestling Sex Ratios n=16 chicks n=26 chicks Gaspe data provided by Yves Aubry, Canadian Wildlife Service
Are females limited during annual cycle? If so, where?
2004 PCR Sexing Results 1:1 Equal  n=25 4:1 Male n=18 3.8:1 Male n=25 1.9:1 Male Island-Wide (n= 142 captures) First-year ...
Two Hypotheses for Mechanisms That Underlie Sexual Habitat Segregation <ul><li>Habitat specialization  = each sex chooses ...
Methods (and Challenges) <ul><li>Active (broadcast elicitation) and passive mist-netting to capture BITH (passive capture ...
 
Mid-winter Mean Sex Ratios n=8 years
 
Sierra de Bahoruco BITH Territories 0.372 0.218
1 st  Year Male Adult Female Adult  Male Adult Male 1 st  Year Male Adult  Female
 
Mid-winter Sex Ratios n=8 years  n=4 years
 
Biotic and Abiotic Differences  Between Sites <ul><li>BAHORUCOS (Male) </li></ul><ul><li>High Elev. (1600-1900 m) </li></u...
Leading Cause of Winter Mortality = Introduced Rats 1/5 2008, 3/15 in 2007, 1/26 2006
Age comparison of Toe nail   13 C values P =0.0159 n=39  (SY=18, ASY=21) t =2.03  13 C values are  significantly differe...
Where are Females Limited? Nest 1:1 sex ratio in clutch Fledge Post Fledging Dispersal 1:1 1:1 Fall Migration 1:1 ? Ratio ...
 
Acknowledgements <ul><li>Field work and data analysis: </li></ul><ul><li>Esteban Garrido, Vinicio Mejia, Elvis Cuevas, Jes...
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Partners in Flight 2008: Bicknell's Thrush

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Partners in Flight 2008: Bicknell's Thrush

  1. 1. Population Limitation in Bicknell’s Thrush: a Female Problem? <ul><li>Chris Rimmer and Kent McFarland – VCE </li></ul><ul><li>Jason Townsend – SUNY ESF </li></ul><ul><li>Kevin Fraser – University of New Brunswick </li></ul>
  2. 2. Partners In Flight = North America Watch List IUCN Red List = Vulnerable ABC/Audubon WatchList = Red List Canada = Candidate for Federal Listing USFWS = Special Concern ME, NH, NY, VT = Special Concern www.bicknellsthrush.org
  3. 3. “ Differential mortality of females during the non-breeding season, resulting from effects of dominance, may thus also contribute to the male-biased sex ratio observed in breeding populations of redstarts and perhaps other species of socially monogamous birds.” (Marra and Holmes 2001) Hispaniola Dominican Republic Haiti
  4. 4. n=4 n=4 n=10 n=3 n=5 n=7 Overall mean = 2.2 males : female n = number years Breeding Adult Sex Ratios Gaspe and Gosford data provided by Yves Aubry, Canadian Wildlife Service
  5. 5. Recapture Probability for Mansfield and Stratton
  6. 6. n=5 nests n=5 nests Nestling Sex Ratios n=16 chicks n=26 chicks Gaspe data provided by Yves Aubry, Canadian Wildlife Service
  7. 7. Are females limited during annual cycle? If so, where?
  8. 8. 2004 PCR Sexing Results 1:1 Equal n=25 4:1 Male n=18 3.8:1 Male n=25 1.9:1 Male Island-Wide (n= 142 captures) First-year birds island-wide: 2.1:1 male n=38 2.4:1 Male n=17
  9. 9. Two Hypotheses for Mechanisms That Underlie Sexual Habitat Segregation <ul><li>Habitat specialization = each sex chooses sex-specific optimal habitat Hooded Warblers (Morton 1990) </li></ul><ul><li>Behavioral Dominance = larger, more aggressive males relegate females and sub-dominant males to sub-par habitat American Redstarts (Marra et al. 1993) </li></ul>
  10. 10. Methods (and Challenges) <ul><li>Active (broadcast elicitation) and passive mist-netting to capture BITH (passive capture rate = 1/800 net hours) </li></ul><ul><li>Blood samples collected from all birds for molecular sexing </li></ul><ul><li>Radio telemetry to examine territoriality and within-season survivorship. </li></ul><ul><li>Survivorship analyses via mark-recapture (re-sightings almost nonexistent, within-season recaptures difficult) </li></ul>
  11. 12. Mid-winter Mean Sex Ratios n=8 years
  12. 14. Sierra de Bahoruco BITH Territories 0.372 0.218
  13. 15. 1 st Year Male Adult Female Adult Male Adult Male 1 st Year Male Adult Female
  14. 17. Mid-winter Sex Ratios n=8 years n=4 years
  15. 19. Biotic and Abiotic Differences Between Sites <ul><li>BAHORUCOS (Male) </li></ul><ul><li>High Elev. (1600-1900 m) </li></ul><ul><li>“ Pristine” Montane Forest </li></ul><ul><li>Dense Understory </li></ul><ul><li>Scarcity of Soft Fruit </li></ul><ul><li>Abundance of Arthropods </li></ul><ul><li>Moderate Rainfall </li></ul><ul><li>Thin Karst Soils </li></ul><ul><li>Rat population moderate </li></ul><ul><li>CANELA (Equal) </li></ul><ul><li>Mid Elev. (250-500 m) </li></ul><ul><li>Recovering Forest </li></ul><ul><li>Open Understory </li></ul><ul><li>Abundance of Soft Fruit </li></ul><ul><li>Relatively Fewer Arthropods </li></ul><ul><li>Heavy Rainfall </li></ul><ul><li>Dense Clay Soils </li></ul><ul><li>Rat population high </li></ul>
  16. 20. Leading Cause of Winter Mortality = Introduced Rats 1/5 2008, 3/15 in 2007, 1/26 2006
  17. 21. Age comparison of Toe nail  13 C values P =0.0159 n=39 (SY=18, ASY=21) t =2.03  13 C values are significantly different between SY (5) and ASY (6) birds Suggests habitat use/ segregation by age SY birds in wetter sites dominated by C 3 plants K. Fraser
  18. 22. Where are Females Limited? Nest 1:1 sex ratio in clutch Fledge Post Fledging Dispersal 1:1 1:1 Fall Migration 1:1 ? Ratio ? 2:1 Spring Migration 2:1 Breeding Grounds >2:1 Primary Forest >2:1 Disturbed Forest ~1:1 Habitat and Territory Selection
  19. 24. Acknowledgements <ul><li>Field work and data analysis: </li></ul><ul><li>Esteban Garrido, Vinicio Mejia, Elvis Cuevas, Jesus Almonte </li></ul><ul><li>Jorge Brocca – Sociedad Ornithologica de la Hispaniola </li></ul><ul><li>Juan Klavins and Sarah Frey, VCE </li></ul><ul><li>Jim Goetz, Cornell Lab of Ornithology </li></ul><ul><li>Andrea Townsend, Cornell Lab of Ornithology </li></ul><ul><li>Scott Sillett, Smithsonian Migratory Bird Center </li></ul><ul><li>Yves Aubry,Canadian Wildlife Service </li></ul><ul><li>Funding: </li></ul><ul><li>Nuttall Ornithological Club </li></ul><ul><li>Stewart Family Foundation </li></ul><ul><li>Thomas Marshall Foundation </li></ul><ul><li>The Nature Conservancy </li></ul><ul><li>U.S. Fish and Wildlife Service </li></ul>

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