Banff National Park of Canada
Trans-Canada Highway Twinning
The Banff Wildlife Crossings Project Report, 2002
HOW DO WE KNOW IF THIS MITIGATION IS WORKING?
Is Road Mortality Reduced?
Mitigation measures are intended to reduce the number of wildlife-vehicle collisions, or potential vehicle collisions, such as animals getting onto the highway right-of-way. If these measures are effective, they should show a reduction in the number of road-kills between pre-mitigation compared to post-mitigation. Significant reductions in road-related mortality should allow for viable or healthy wildlife populations, however other factors such as population density, and the extent of other mortality sources will ultimately influence the viability of wildlife populations.
Do Wildlife Crossing Structures Work?
There is no general answer to the question, "Do wildlife crossing structures work?" most people believe that if animals use it, then it must be working. As more wildlife species are added to the equation, the answer becomes even more complex. We believe that wildlife crossing structures should function for multiple wildlife species rather than a single, flagship or emblematic species, (e.g. grizzly bears) in order to maintain ecological integrity.
There are no established guidelines to rigorously evaluate whether wildlife crossing structures meet their intended purpose. One of the problems is clearly deciding what is the intended purpose and what are the expectations of a crossing structure. We developed ecological criteria that could be used as guidelines to evaluate how well crossing structure are working. These criteria range from simple measurements to complex, long-term studies:
1) Do they maintain habitat connectivity? Species must be present on both sides of a structure, and a minimum amount of passage must be detected
2) Do they maintain genetic interchange? Passage by breeding adults must occur, primarily males during the mating season in order to avoid inbreeding among populations
3) Do they ensure biological requirements are being met? Ensure populations are finding food, cover and mates, if not, this could lead to reduced breeding opportunities, lowered reproductive and survival rates, occupation of poor habitat, and increased vulnerability to predation.
4) Do they allow for dispersal and recolonisation? Animals need to disperse out of maternal ranges into areas where there have been long absences or local extinctions in order to recolonise or replenish the population.
5) Do they maintain metapopulation and ecosystem processes? If one population of animals becomes extinct another population of animals must recolonise the area in order for the population to persist.
Long-term monitoring along with concurrent ecological studies of radio-marked individuals in the Bow Valley will allow us to assess whether species biological requirements and ultimately individual fitness is being maintained.
How To Interpret Wildlife Crossing Data
Summarizing the observed counts of animal passage and comparing numbers between species is often done to judge how well a crossing structure performs. One would have to be careful when interpreting this data, as count data has to be looked at along with population size. Obviously 20 counts of rare species A will appear low compared to 500 crossings by very common species B, however 20 counts could be high if there are only 10 animals in the study area.
Another frequent oversight is to examine counts of animal passage, and interpret a low number of passages as avoidance and a high number as preference. It is not possible to judge structure use based on counts as indicated above. There can be many reasons not entirely obvious at first glance why certain wildlife is not using a type of crossing structure or perhaps less than might be expected. One explanation is that wildlife distributions and habitat quality are not uniformly distributed where the structures are located. Their populations vary greatly up and down the highway. Topography and aspect are important in explaining species presence or absence, as is habitat quality. For example, in areas where sheep are absent, there are no sheep crossings at nearby structures. We cannot interpret this as sheep avoiding a certain type of structure when sheep are not present in the area.
For more information see Chapter 7 in Final Report
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