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Modelling survival from fieldwork data: a case study on the social bat Molossus molossus

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XIIIth European Bat Research Symposium, Sibenik (Croatia)
1-5 September 2014.

Published in: Science
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Modelling survival from fieldwork data: a case study on the social bat Molossus molossus

  1. 1. Yann Gager Modelling survival from fieldwork data: a case study on the social bat Molossus molossus
  2. 2. Acknowledgements Dina Dechmann Teague O’Mara Olivier Gimenez Rachel Page + many fieldwork assistants
  3. 3. Many animals are social…but why?
  4. 4. Many animals are social…but why? Balance of costs and benefits of group living
  5. 5. Sociality in bats Tropics Group hunting? Temperate zones (summer) Social thermoregulation Group hunting
  6. 6. Social foraging in insectivorous bats [Safi & Kerth 2007] - Energetically limited (small size, flight + echolocation) - Extreme specialization (narrow wings + ephemeral insects) - Acoustic information transfer on site between roost members
  7. 7. How is survival related to group size ? Group size Survival - Survival benefits/costs associated with group living?
  8. 8. [Dechmann et al. 2010]
  9. 9. Collection of survival data 1350 animals transpondered during regular captures 7 roosts with automated readers 1980 « days » Capture-recapture 14 sites – 77 captures
  10. 10. Roost variation Monthly variation 1a. Size of groups: spatial variation
  11. 11. 2. Survival analyses (capture) - Data: capture-recapture (285 adult females) - Analysis: Cox-proportional hazard regression - Results: Effect of marking year Variable p Marking year 0.00966 *** Initial group size 0.33938 Mean group size 0.97945 Site 0.81306 GLOBAL 0.12201
  12. 12. 3. Survival analyses (transponder-reader) - Data: 4 sites followed over 15 months (59 adult females) - Aim: Model monthly survival - Analysis: Model comparison (Multi-state Mark-Recapture) - Results: Group size as the best explanatory variable Model QAICc ΔQAICc No. Of parameters Group size 1546.1 0.0 20 Month 1583.6 19.5 28 Marking year 1773.6 209.5 8 . 1786.8 222.7 4 Site 1791.2 227.1 7
  13. 13. 3. Survival analyses (transponder-reader)
  14. 14. To conclude Conclusions 1- Survival benefits with increased group size 2- Constraints to medium groups Perspectives: - Effect of group size on foraging efficiency - Relatedness between group members
  15. 15. Thank you!

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