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  • 1. Bicknell's and Swainson's thrushes in regenerating New Brunswick clearcuts: niche separation by nest site and diet Emily A. McKinnon, Kevin C. Fraser, Antony W. Diamond University of New Brunswick, Fredericton
  • 2. Outline
    • Intro
      • BITH and SWTH
      • NB context
      • niches
    • Part 1: Nest site
      • nest patch vegetation
    • Part 2: Diet
      • trophic niche width
      • SIA
    • Summary
  • 3. Intro: study species Catharus bicknelli = BITH Catharus ustulatus = SWTH
  • 4. Bicknell’s Thrush
    • ‘ Specialist’
    • Stunted, dense balsam fir and spruce
    • High elevation
    • Endemic to NE NA
  • 5. Swainson’s Thrush
    • ‘ generalist’
    • Found in many forest types
    • abundant
  • 6. Study Site
  • 7. NB highlands
    • Heavily managed for timber/pulpwood
    • Lots of balsam fir
    • BITH in regenerating clearcuts - recently colonized?
  • 8. Niche separation
    • Sabo 1980: New Hampshire montane bird community
    SWTH BITH
  • 9. Niche separation
    • Do BITH and SWTH nest in similar locations?
    • Do BITH and SWTH show overlapping dietary niche?
    • Is BITH really a ‘specialist’?
  • 10. Part 1: Nest site
  • 11. Nest patch characteristics
    • 5-m radius patch centered on the nest
    • non-nest patches selected 100m away from nest patch
            = non-nest site = nest site
  • 12. Nest patch analyses
    • Nest patch data  biologically meaningful variables
      • Snags
      • % balsam fir
      • Small trees
      • Hardwoods
      • Total density
  • 13. Nest patch composition
  • 14. BITH vs. SWTH
  • 15. BITH and SWTH nests Non-nest patch
  • 16. BITH and SWTH
    • BITH are more selective than SWTH
    • Differences in vegetation association on a small scale
  • 17. Part 2: Diet
    • Do they consume different foods?
  • 18. Dietary studies
    • Morphology (Dilger 1956)
      • BITH more ground forager, SWTH arboreal
    • Foraging technique/location (Sabo 1980)
      • BITH ground forager, SWTH generalist
    • Stomach contents analysis (Beal 1918, Wallace 1939)
      • BITH: Coleoptera, Hymenoptera, SWTH:especially Diptera
  • 19. ‘ New’ method to quantify diet
    • Stable Isotope Analysis (SIA)
    • Isotopic niche = trophic niche
    15 N/ 14 N 15 N / 14 N 15 N / 14 N 15 N / 14 N 14 N 14 N 14 N
  • 20. Isotope timelines bone muscle whole blood/RBC plasma liver feather Long time Short time feces
  • 21. Isotopic niche Bearhop et al. 2004 BITH? SWTH
  • 22. Collecting isotope samples
  • 23. When does blood reflect local diet?
    •  D = H 2 /H 1
    • Expected value: -83‰ + fractionation
  • 24.  D throws a wrench in the plan BITH SWTH 20 June
  • 25. SWTH: Specialist or generalist?
  • 26. BITH: Specialist or generalist?
  • 27. Summary Nest patch Diet Very specialized Very generalized Very specialized Very generalized SWTH BITH
  • 28. Summary
    • BITH choose nest patches on a small scale
      • Suggests ability to nest in small patches?
    • SWTH nest patches are less specific
      • less affected by management?
    • BITH - Type 2 generalists
      • Individual specialization?
    • SWTH - Type 1 generalists
      • reduced competition with BITH?
  • 29. Future work
    • Nest patch characteristics- How flexible are they?
    • Diet throughout the season
    • Could blood tell us where BITH or SWTH came from?
  • 30. Acknowledgements
    • Committee: Dr. D. MacLean, Dr. D. Keppie
    • T. Vanbuskirk, B. Whittam, G. Campbell, C. Rimmer, K. McFarland, A. Albert, R. Aracil, H. Askanas, K. Friars, M. Godin, C. Wegenschimmel, Operations 1 Staff, Mark McLelland at the Governor’s Lodge
  • 31. Questions? SWTH bad hair day.