Bats, Roads & Railways Improving survey and assessment Anna Berthinussen and John Altringham
Format Background 10 min + 5 min discussion Methodology Landscape scale assessment 10 min + 5 min discussion Mitigation assessment 10 min + 5 discussion CIEEM training day 29 September, Leeds Defra report WC1060 Guidance Note for SNCOs General discussion 15 min
Roads can affect bats in many ways Negative Habitat loss the road itself Habitat degradation noise, light and chemical pollution These effects act at different rates and are cumulative.. and the detrimental effects are likely to lead to population decline Collision mortality Barrier effect fragmenting home range Positive Habitat creation, enhancement, increased connectivity ALONG roads
We set out to look for evidence of these effects by asking a simple question: Are bat activity and diversity related to proximity to motorways? Effects are currently assumed and mitigation is obligatory, so we also asked: Are current mitigation methods effective at getting bats safely across roads?
M6 Cumbria Are bat activity and diversity related to proximity to a motorway? 20 X 1.6 km transects perpendicular to the road at each site Recorded bat activity and number of species at different distances along transects M5 Somerset & Devon
Bat passes 0 20 40 // 100 Probability 0.6 0.7 0.8 0.9 After accounting for weather and habitat: Total bat activity increased 3-fold between 0 and 1600 m from the road The number of species also increased significantly with distance Habitat quality mitigated against the effects of the road Good habitat Poor habitat 0 800 1600 Distance (m) 0 800 1600 Distance (m) Berthinussen A and Altringham JD. (2012) The effects of a major road on bat activity and diversity. Journal of Applied Ecology. 49, 82-89.
Defra funding extended our studies: having looked at existing motorways, we went on to find: Reduced activity/diversity on motorways during and after construction/upgrade Reduced activity/diversity on some A roads (incl. single carriageway Reduced activity/diversity on some railways
Roads do affect bats impact assessment and mitigation ARE important Has mitigation been effective? Are we helping bats cross roads safely? We looked at underpasses and bat gantries Designed to: Increase road permeability Reduce roadkill
Underpasses can be effective, but construction and alignment are critical Effective ineffective Berthinussen A and Altringham JD. (2012) Do bat gantries and underpasses help bats cross roads safely. PLoS ONE 7(6): e38775.
Gantries do not work 9-year old gantry. Kernel intensity estimation
Gantries of a different design on the A11 also don t work
New work - gantries of a different design on the A11 also don t work Few bats were recorded at any gantry on A11 Has construction already driven the bats away? Were there many bats present before construction?
Some good news the A487 overbridge
Better news Scotney Castle green bridge
What have we learned? Roads and rail can have a profound effect on bat activity and diversity Causes: habitat loss, degradation, fragmentation and roadkill Mitigation is therefore essential Current practices are inadequate: Goals are ill-defined Monitoring is often badly designed and/or not carried out Mitigation effectiveness often untested or shown to be failing Hence the defra project and this workshop... Our brief was to develop cost-effective survey methods at landscape and mitigation scheme level based on our work...
Survey methods Landscape scale assessment: Large scale transect study to assess impact Mitigation assessment: Observational surveys at crossing points and mitigation crossing structures to assess effectiveness
Landscape scale assessment Large scale transect study Aim: to provide baseline data and reveal changes in bat activity and diversity across the landscape surrounding the road/railway?? Statistical modelling is used to detect changes A reduction in bat activity and/or diversity indicates the strong likelihood of a negative impact on nearby bat populations
Landscape scale assessment Methods 10 x 1 km walked transects perpendicular to the road/railway on both sides Walk at a set steady pace (~5 km/h) Record bat activity at 10 min stationary spot checks at 100 m intervals Transects commence 30 min after sunset and are walked in different directions
Weather variables: Temperature ( C), wind speed (km/h), cloud cover (%) and general weather conditions To assess if conditions suitable Habitat variables: Can be complex and difficult to quantify Simplified using grading system to classify variables of interest Grade Habitat type 1 Fence or wall lining road/path & open fields beyond 2 Hedges/shrubby verges lining road/path & open fields beyond 3 Intermittent medium trees/bushes lining road/path & open fields beyond 4 Intermittent tall trees lining road/path & open fields beyond 5 Continuous tall tree cover lining road/path with woodland &/or open fields beyond
Landscape scale assessment Quantitative analysis Identify bat passes to species or genus using automated call identification software e.g. BatClassify (www.bitbucket.org/chrisscott/batclassify) Count the number of bat passes per spot check Statistical modelling to test for road effects: Generalised Estimating Equations (GEE) multiple regression model Straight forward to run in the R program We provide full instructions and R code! (www.r-project.org)
Landscape scale assessment Presenting the results Model predictions % change in bat activity/diversity with distance from the road/railway Plots of bat activity/diversity against distance from the road/railway Interpreting the results Statistical significance is not critical Detrimental effects = a decline in bat activity and/or diversity over 20% (regardless of statistical significance) or less than 10% with a significance level of P < 0.05
Landscape scale assessment Questions?
Mitigation assessment Observational surveys to assess effectiveness of mitigation structures Pre-construction: survey bats along linear habitat feature that will be severed by the road Post construction: survey mitigation structure Has the number of bats using the commuting route changed since construction? Is the structure guiding crossing bats safely over/under roads?
Mitigation assessment Use v s effectiveness: the whole picture With post-construction data we can compare the proportions of bats using the structure to those not using it or at risk of collisions with traffic But, to fully assess effectiveness, comparisons must also be made before and after construction
Mitigation assessment Methods Visual observations of crossing bats paired with echolocation recordings 6 x 60 min surveys at dusk or dawn per site Count crossing bats and record flight height and distance from crossing structures - LED markers for distance - Night vision and infra-red lights in underpasses
Mitigation assessment Analysis Set definitions for use of the structure and safe/unsafe crossing height Use boxplots / percentages to compare the proportions of bats using the structure to those not using it or at risk of collisions with traffic Wilcoxon Signed Rank test to compare numbers crossing before and after construction Use = crossing within 5 m of structure at a safe height (e.g. gantries/bridges) or through an underpass Safe crossing height: > 5 m above road
Kernel intensity estimation Visual plot of data showing density of crossing bats
Mitigation assessment Interpretation For a crossing structure to be effective: A similar number of bats must be using the commuting route before and after construction AND at least 90% of bats must be using the structure to cross the road safely
Mitigation assessment Questions?
Defra report: Berthinussen, A. and Altringham, J. (2015) Development of a cost-effective method for monitoring the effectiveness of mitigation for bats crossing linear transport infrastructure. Defra contract report WC1060 Available at: http://tinyurl.com/batsandroads CIEEM training course: Survey and monitoring of road and rail and associated mitigation schemes for bats: pre, during and post-construction 29 th September 2016 University of Leeds