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McKinnon AOU 2009

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    McKinnon AOU 2009 McKinnon AOU 2009 Presentation Transcript

    • 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
    • Outline
      • Intro
        • BITH and SWTH
        • NB context
        • niches
      • Part 1: Nest site
        • nest patch vegetation
      • Part 2: Diet
        • trophic niche width
        • SIA
      • Summary
    • Intro: study species Catharus bicknelli = BITH Catharus ustulatus = SWTH
    • Bicknell’s Thrush
      • ‘ Specialist’
      • Stunted, dense balsam fir and spruce
      • High elevation
      • Endemic to NE NA
    • Swainson’s Thrush
      • ‘ generalist’
      • Found in many forest types
      • abundant
    • Study Site
    • NB highlands
      • Heavily managed for timber/pulpwood
      • Lots of balsam fir
      • BITH in regenerating clearcuts - recently colonized?
    • Niche separation
      • Sabo 1980: New Hampshire montane bird community
      SWTH BITH
    • Niche separation
      • Do BITH and SWTH nest in similar locations?
      • Do BITH and SWTH show overlapping dietary niche?
      • Is BITH really a ‘specialist’?
    • Part 1: Nest site
    • 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
    • Nest patch analyses
      • Nest patch data  biologically meaningful variables
        • Snags
        • % balsam fir
        • Small trees
        • Hardwoods
        • Total density
    • Nest patch composition
    • BITH vs. SWTH
    • BITH and SWTH nests Non-nest patch
    • BITH and SWTH
      • BITH are more selective than SWTH
      • Differences in vegetation association on a small scale
    • Part 2: Diet
      • Do they consume different foods?
    • 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
    • ‘ 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
    • Isotope timelines bone muscle whole blood/RBC plasma liver feather Long time Short time feces
    • Isotopic niche Bearhop et al. 2004 BITH? SWTH
    • Collecting isotope samples
    • When does blood reflect local diet?
      •  D = H 2 /H 1
      • Expected value: -83‰ + fractionation
    •  D throws a wrench in the plan BITH SWTH 20 June
    • SWTH: Specialist or generalist?
    • BITH: Specialist or generalist?
    • Summary Nest patch Diet Very specialized Very generalized Very specialized Very generalized SWTH BITH
    • 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?
    • Future work
      • Nest patch characteristics- How flexible are they?
      • Diet throughout the season
      • Could blood tell us where BITH or SWTH came from?
    • 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
    • Questions? SWTH bad hair day.