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  1. 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. 2. Outline <ul><li>Intro </li></ul><ul><ul><li>BITH and SWTH </li></ul></ul><ul><ul><li>NB context </li></ul></ul><ul><ul><li>niches </li></ul></ul><ul><li>Part 1: Nest site </li></ul><ul><ul><li>nest patch vegetation </li></ul></ul><ul><li>Part 2: Diet </li></ul><ul><ul><li>trophic niche width </li></ul></ul><ul><ul><li>SIA </li></ul></ul><ul><li>Summary </li></ul>
  3. 3. Intro: study species Catharus bicknelli = BITH Catharus ustulatus = SWTH
  4. 4. Bicknell’s Thrush <ul><li>‘ Specialist’ </li></ul><ul><li>Stunted, dense balsam fir and spruce </li></ul><ul><li>High elevation </li></ul><ul><li>Endemic to NE NA </li></ul>
  5. 5. Swainson’s Thrush <ul><li>‘ generalist’ </li></ul><ul><li>Found in many forest types </li></ul><ul><li>abundant </li></ul>
  6. 6. Study Site
  7. 7. NB highlands <ul><li>Heavily managed for timber/pulpwood </li></ul><ul><li>Lots of balsam fir </li></ul><ul><li>BITH in regenerating clearcuts - recently colonized? </li></ul>
  8. 8. Niche separation <ul><li>Sabo 1980: New Hampshire montane bird community </li></ul>SWTH BITH
  9. 9. Niche separation <ul><li>Do BITH and SWTH nest in similar locations? </li></ul><ul><li>Do BITH and SWTH show overlapping dietary niche? </li></ul><ul><li>Is BITH really a ‘specialist’? </li></ul>
  10. 10. Part 1: Nest site
  11. 11. Nest patch characteristics <ul><li>5-m radius patch centered on the nest </li></ul><ul><li>non-nest patches selected 100m away from nest patch </li></ul>        = non-nest site = nest site
  12. 12. Nest patch analyses <ul><li>Nest patch data  biologically meaningful variables </li></ul><ul><ul><li>Snags </li></ul></ul><ul><ul><li>% balsam fir </li></ul></ul><ul><ul><li>Small trees </li></ul></ul><ul><ul><li>Hardwoods </li></ul></ul><ul><ul><li>Total density </li></ul></ul>
  13. 13. Nest patch composition
  14. 14. BITH vs. SWTH
  15. 15. BITH and SWTH nests Non-nest patch
  16. 16. BITH and SWTH <ul><li>BITH are more selective than SWTH </li></ul><ul><li>Differences in vegetation association on a small scale </li></ul>
  17. 17. Part 2: Diet <ul><li>Do they consume different foods? </li></ul>
  18. 18. Dietary studies <ul><li>Morphology (Dilger 1956) </li></ul><ul><ul><li>BITH more ground forager, SWTH arboreal </li></ul></ul><ul><li>Foraging technique/location (Sabo 1980) </li></ul><ul><ul><li>BITH ground forager, SWTH generalist </li></ul></ul><ul><li>Stomach contents analysis (Beal 1918, Wallace 1939) </li></ul><ul><ul><li>BITH: Coleoptera, Hymenoptera, SWTH:especially Diptera </li></ul></ul>
  19. 19. ‘ New’ method to quantify diet <ul><li>Stable Isotope Analysis (SIA) </li></ul><ul><li>Isotopic niche = trophic niche </li></ul>15 N/ 14 N 15 N / 14 N 15 N / 14 N 15 N / 14 N 14 N 14 N 14 N
  20. 20. Isotope timelines bone muscle whole blood/RBC plasma liver feather Long time Short time feces
  21. 21. Isotopic niche Bearhop et al. 2004 BITH? SWTH
  22. 22. Collecting isotope samples
  23. 23. When does blood reflect local diet? <ul><li> D = H 2 /H 1 </li></ul><ul><li>Expected value: -83‰ + fractionation </li></ul>
  24. 24.  D throws a wrench in the plan BITH SWTH 20 June
  25. 25. SWTH: Specialist or generalist?
  26. 26. BITH: Specialist or generalist?
  27. 27. Summary Nest patch Diet Very specialized Very generalized Very specialized Very generalized SWTH BITH
  28. 28. Summary <ul><li>BITH choose nest patches on a small scale </li></ul><ul><ul><li>Suggests ability to nest in small patches? </li></ul></ul><ul><li>SWTH nest patches are less specific </li></ul><ul><ul><li>less affected by management? </li></ul></ul><ul><li>BITH - Type 2 generalists </li></ul><ul><ul><li>Individual specialization? </li></ul></ul><ul><li>SWTH - Type 1 generalists </li></ul><ul><ul><li>reduced competition with BITH? </li></ul></ul>
  29. 29. Future work <ul><li>Nest patch characteristics- How flexible are they? </li></ul><ul><li>Diet throughout the season </li></ul><ul><li>Could blood tell us where BITH or SWTH came from? </li></ul>
  30. 30. Acknowledgements <ul><li>Committee: Dr. D. MacLean, Dr. D. Keppie </li></ul><ul><li>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 </li></ul>
  31. 31. Questions? SWTH bad hair day.