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Nest Site and Diet Separation in Bicknell's and Swainson's Thrushes
- 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 • Intro – BITH and SWTH – NB context – niches • Part 1: Nest site – nest patch vegetation • Part 2: Diet – trophic niche width – SIA • Summary
- 3. 3 Intro: study species Catharus bicknelli = BITH Catharus ustulatus = SWTH
- 4. 4 Bicknell’s Thrush • ‘Specialist’ • Stunted, dense balsam fir and spruce • High elevation • Endemic to NE NA
- 5. 5 Swainson’s Thrush • ‘generalist’ • Found in many forest types • abundant
- 6. 6 Study Site
- 7. 7 NB highlands • Heavily managed for timber/pulpwood • Lots of balsam fir • BITH in regenerating clearcuts - recently colonized?
- 8. 8 Niche separation Sabo 1980: New Hampshire montane bird community SWTHBITH
- 9. 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. 10 Part 1: Nest site
- 11. 11 Nest patch characteristics = non-nest site = nest site • 5-m radius patch centered on the nest • non-nest patches selected 100m away from nest patch
- 12. 12 Nest patch analyses • Nest patch data biologically meaningful variables – Snags – % balsam fir – Small trees – Hardwoods – Total density
- 14. 14 BITH vs. SWTH
- 15. 15 BITH and SWTH nests Non-nest patch
- 16. 16 BITH and SWTH • BITH are more selective than SWTH • Differences in vegetation association on a small scale
- 17. 17 Part 2: Diet • Do they consume different foods?
- 18. 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. 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. 20 Isotope timelines bone muscle whole blood/RBC plasma liver feather Long time Short time feces
- 21. 21 Isotopic niche BITH?SWTH Bearhop et al. 2004
- 23. 23 When does blood reflect local diet? ∀δD = H2 /H1 • Expected value: -83‰ + fractionation
- 24. 24 δD throws a wrench in the plan BITH SWTH 20 June
- 25. 25 SWTH: Specialist or generalist?
- 26. 26 BITH: Specialist or generalist?
- 28. 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. 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. 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. 31 Questions? SWTH bad hair day.