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

Yann Gager

Modelling survival from fieldwork data:

a case study on the social bat Molossus molossus

Acknowledgements

Dina Dechmann Teague O’Mara

Olivier Gimenez Rachel Page

+ many fieldwork assistants

Many animals are social…but why?

Many animals are social…but why?

Balance of costsand benefits of group

living

Sociality in bats

Tropics

Group hunting?

Temperate zones (summer)

Social thermoregulation Group hunting

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

How is survival related to group size ?

Group size

Su

rviv

al

- Survival benefits/costs associated with group living?

[Dechmann et al. 2010]

Collection of survival data

1350 animals transpondered

during regular captures

7 roosts with automated readers

1980 « days »

Capture-recapture

14 sites – 77 captures

Roost variation

Monthly variation

1a. Size of groups: spatial variation

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

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

3. Survival analyses (transponder-reader)

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

Thank you!