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Wildlife passages – How to evaluate their effectiveness? Edgar van der Grift

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Presentation on theme: "Wildlife passages – How to evaluate their effectiveness? Edgar van der Grift"— Presentation transcript:

1 Wildlife passages – How to evaluate their effectiveness? Edgar van der Grift

2 Worldwide many wildlife passages in all forms/sizes, but…. Dassentunnel

3 …do they work?

4 Much baseline information about passage performance available!


6 Knowledge gab 1 Many studies about passage use… But little knowledge about passage effectiveness!

7 Knowledge gab 2 Some studies address effectiveness… But in most of them the effectiveness of wildlife passages on population persistence remains unclear!

8 Wildlife passage use Studying use is not useless! However: Use Effectiveness Use does not provide evidence for effects of wildlife passages on population persistence !

9 Use Effectiveness 3 x 1 badger? Research: 3 crossings of badger per time period T But: what does it mean? 1 x 3 badgers?

10 Use Effectiveness After road construction: Before road construction: 3 x 3 badgers 1 x 3 badgers Usually no monitoring before !

11 Wildlife passage effectiveness Definition: The extent to which the objectives (= desired effect) for a wildlife passage are reached no objective = no effectiveness (And: no problem = no objective)

12 Setting SMART objectives S=SpecificWhat are we going to do? M=MeasurableHow much? A=AcceptableIs there enough support? R=RealisticIs it possible what we want to do? T=Time frameWhen are we finished? Objective for each project must be specific to the location, species of concern and nature of the problem

13 Does it meet our objectives?

14 Working out a monitoring approach What are suitable research species? What are suitable research sites? What is the best study design (options)? Which research methods (surveys/analyses) are most promising? What measurement schemes should be used? What are the estimated costs?

15 Choose appropriate research species Species is (highly) vulnerable for road impacts Proven use of wildlife passages Road impact is measurable Species allows for study design with high inferential strength

16 Choose appropriate research sites Select locations where wildlife passages are expected to make a large difference (e.g. by modeling population viability) Species X:not viable viable highly viable with infrawithout infra

17 Choose appropriate study design: (B)BACI, BA or CI Before road BeforeAfter construction mitigation mitigation Impact Control 1 Control 2 (Roedenbeck et al., 2007)

18 Study design in literature review (n=123 studies): Before-After (BA) comparison approach: n=15 Use of controls in <10 studies Most studies retrospective: only survey of crossing structures after construction In practice: trade-offs between perfect study design and reality! Before situation already in the past No controls, no replication Randomisation not feasible Limited budget ….

19 Do not only include the wildlife passage in your study design! <50% studies in literature review incorporated assessment of presence/abundance target species around wildlife crossing Not measuring the population adjacent to road may result in wrong conclusions about wildlife passage performance Example: Reduction in roadkill does not necessarily mean the crossing structure is effective

20 Importance of population surveys BEFOREAFTER Effect Example 1: Roadkill % Population size % Example 2: Roadkill % Population size %









29 Relate to abundance of animals in adjacent habitat

30 Select appropriate research methods


32 Monitoring! Photo: Bart Siebelink

33 Review: Tracking pads (n=74) Video / infra-red still cameras (n=36) Collection/identification scats (n=16) Direct observations (n=13) Trapping (n=12) Collection/identification hair (n=8) Radio-tracking (n=7) Trail monitors/wildlife counters (n=6) Other (including dusting with fluorescent pigment)

34 Select appropriate research methods Go (sometimes) off the beaten track! Large species over-represented in existing studies, partly because of chosen research methods New techniques in development: e.g. genetics, PIT tags

35 Wildlife overpass Groene Woud

36 Wetland zoneDry zone


38 Number of observations adults/juveniles (n=968) Wildlife overpass Distribution amphibians across overpass Common toad Common frog Smooth newt Crested newt Green frog

39 Significant more amphibians in wetland zone Number of observations

40 Efficiency method artificial refugia Number of observations


42 Crested newts: Belly patterns Identification of individuals and individual movements across the overpass

43 Crested newts: Belly patterns Identification of individuals and individual movements across the overpass

44 Appropriate measurement scheme Appropriate monitoring period (review: 4 nights – 8 yrs) Appropriate frequency of measurements within period (review: 1/day – 1/week) Appropriate number of impact and control sites Recommendation: Assessment of measurement scheme on the basis of dynamic population model simulations of monitoring

45 Appropriate measurement scheme Monitoring changes in populations Survey: 26 yearsSurvey: 12 years 1 study site10 study sites 100% 80% 60% 40% 20% 100% 80% 60% 40% 20%

46 Maximize inferential strength (validity) Inferential strength = high probability and low uncertainty that research result is true Dependent on: Number of competing hypotheses tested Extent of extrapolation Study design Measurement scheme

47 Implications Without studies with high IS it will be difficult to prove the effectiveness of defragmentation programs and to justify investments Correlation between increasing IS and increasing costs However: investment in a few good but costly experiments should be prefered above numerous poor experiments at low costs Experiments with high IS carried out over the relevant temporal and spatial time scales may not be feasible in isolated studies, but may be conducted in collaborative (international) networks of researchers

48 Complex problem: time for collaboration...! This badger gate is for 94.68% effective!

49 Use Effectiveness Questions and discussion

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