Two bat schemes that didn’t make it NL 1990-1999

1. Two bat schemes that didn’t make it NL 1990-1999 Rombout de Wijs

2. Schemes for monitoring bats • Hibernacula • Colonies/summer roosts • Point & line counts for passing bats • Transect counts advertising bats

3. Schemes for monitoring bats • Hibernacula • Colonies/summer roosts • Point & line counts for passing bats • Transect counts advertising bats

4. Point/line counts • transects non-random selected (near home) • 1 main type of habitat • 4 km (walk) to 15 km (bike) • 20 points and 20 lines in between • minimum distance between points 200m (walk) or 400m (bike) • points close to water if possible • at least some suboptimal points

5. Transect 7: Schaep & Burgh

6. Point/line counts • detector tuned to 42 kHz • 3 minutes at points • variables at each point/line: • presence • maximum • total # passes • start at 1-1.5 hr after sunset • temperature > 8°C

7. Point/line counts • counting each month April-September • in middle of month (10-20th) • since 1997 only in May, July and August and only at points

8. 17 transects in total • mainly central NL

10. Number of counts/year

11. Species observed at transects

12. More details methodology (results from the 1999 paper) • variables strongly correlated, but sum of passes showed much variation. Risk of saturation in presence • results points and lines strongly correlated, but variation lower at points • no difference in indication value of mean and maximum value per season • species showed different seasonal variation, therefore 3-6 counts necessary: later analysis showed 3 counts sufficient • number of transects needed is 100 for detecting differences between years of 20-40%, but rule of thumb CBS adopted: 25-50 transects for detecting trends over 5-10 years (for each stratification layer)

13. Trends 6 species using model TRIM and using variable Presence

14. Why giving up? • insufficient # transects • insufficient # volunteers, in spite: • much effort to arouse interest (newsletter, talks) • making field work easier: only in 3 months (was 6) and only at points (was including lines) • financing stopped Scheme abandoned

15. Schemes for monitoring bats • Hibernacula • Colonies/summer roosts • Point & line counts for passing bats • Transect counts advertising bats

16. Schemes for monitoring bats • Hibernacula • Colonies/summer roosts • Point & line counts for passing bats • Transect counts advertising bats

17. Transect counts advertising bats • non random selected (near home) • 2.5 - 8.0 km • walking or cycling at 5km/hr • 6 counts 15 Aug. - 30 Sept. • start 1 hr after sunset • temp. > 8°C • detector tuned to 20-25 kHz, Pnath checked at 40 kHz (for 2nd part of call) • observations drawn on maps

18. Transect counts advertising bats • end of season: clustering observations to “territoria” • when flying: different individual when >100 m • variables: • maximum at 1 count during season • mean of counts during season

19. 41 transects in total • 23 counted 3 years or more

20. mostly transects • 3 area’s • mostly urban

21. first 2 years experimental • several 1-2 years only

22. species present in 41 transects

23. results from Pnath and Nnoc inaccurate • results from Ppip better • trends similar to PLC

24. Why giving up? • insufficient # Nnoc • insufficient # volunteers • does not add much to PLC • financing stopped Scheme abandoned

25. Should we restart “PLC”? • need of monitoring data on Nnoc and Pnath • need of data other species in summer, especially when not counted in colonies

26. in 1996

27. Better prospects now? • Atlas project longer ago, so more motivation? • better awareness of need of data?? • better methods? • easier, so more volunteers? • less variation, so less counts needed? • better equipment, automatic registration?

28. New methods, new discoveries?Let’s face the challenge of a new start!