Restoring habitat connectivity across transport corridors: identifying high-priority locations for de-fragmentation with the use of an expert-based model

Experimental study designs to improve the evaluation of road mitigation measures for wildlife

“…and/or Which factors are correlated with the number of crossings? However, the state of road ecology has matured since mitigation structures were first developed, and while monitoring rate of crossing is an important first step, and likely appropriate in certain circumstances, it is no longer enough to simply document the use of a structure by the target animal(s) (van der Grift et al, 2013). In addition, we need to answer questions such as: Is the rate of road mortality sufficiently low and/or the rate of crossing sufficiently high to ensure a viable population?…”

“…The general question has to be translated into goals that are highly specified, or SMART: Specific, Measurable, Achievable, Relevant and Time-framed (van der Ree et al, 2007). There are generally two potential objectives in road mitigation goals: (1) no net loss (i.e., road impacts will be fully mitigated), and (2) limited net loss (i.e., a limited road impact will be accepted) (van der Grift et al, 2013). Proper evaluations of the extent to which the full effect of roads have been mitigated (i.e., no net loss/full mitigation) can only be made by comparing treatment sites to road-free control sites (Fig.…”

“…Unfortunately, documenting use of a crossing structure (i.e., 'success' at the individual level) is so far removed from higher level quantities of interest (i.e., population size and persistence), that such studies provide little information as to whether the structure actually mitigates the effect of the road enough to ensure a viable population (van der Grift et al, 2013). Consequently, the influence of these mitigation structures on population viability is unclear for most road-affected species.…”

“…Wildlife crossing structures (e.g., under-or over-passes: amphibian tunnels, badger pipes, ledges in culverts, land bridges, rope bridges, glider poles), combined with fencing to prevent mortality and funnel wildlife towards crossing structures, have gained considerable recent attention by transportation agencies because they enhance landscape connectivity without affecting traffic flow (van der Grift et al, 2013).…”

“…), and specifying a hierarchy of study designs for answering these questions. van der Grift et al (2013) used the principles outlined in Roedenbeck et al (2007) to propose a methodological framework for increasing the inferential strength of mitigation monitoring schemes. Lesbarr eres and proposed the use of such monitoring schemes as a type of experiment, but they did not suggest associated experimental protocols.…”