Are several small wildlife crossing structures better than a single large? Arguments from the perspective of large wildlife conservation

Crossing structures for large wildlife are increasingly being constructed at major roads and railways in many countries and current guidelines for wildlife mitigation at linear infrastructures tend to advocate for large crossing structures sited at major movement corridors for the target species. The concept of movement corridors has, however, been challenged and pinching animal movements into bottlenecks entails risks. In this paper, I address the SLOSS dilemma of road ecology, i.e. the discussion whether a Single Large Or Several Small crossing structures along a linear barrier would produce the most benefit for wildlife, using the case of crossing structures for large wildlife in Sweden. I point out risks, ecological as well as practical, with investing in one large crossing structure and list a number of situations where it may be more beneficial to distribute the conservation efforts in the landscape by constructing several smaller crossing structures; for example, when the ecological knowledge is insufficient, when animal interactions are expected to be significant, when the landscape changes over time or when future human development cannot be controlled. I argue that such situations are often what infrastructure planning faces and that the default strategy, therefore, should be to distribute, rather than to concentrate passage opportunities along major transport infrastructures. I suggest that distributing passage opportunities over several smaller crossing structures would convey a risk diversification and that this strategy could facilitate the planning of wildlife mitigation. What to choose would however depend on, inter alia, landscape composition and ecology and on relationships amongst target species. A single large structure should be selected where it is likely that it can serve a large proportion of target animals and where the long-term functionality of the crossing structure can be guaranteed. New research is needed to support trade-offs between size and number of crossing structures. Cost-effectiveness analyses of wildlife crossing structures are currently rare and need to be further explored. Camera trapping and video surveillance of crossing structures provide opportunities to analyse details concerning, for example, any individual biases according to sex, age, status and grouping and any antagonism between species and individuals. Wildlife ecology research needs to better address questions posed by road and railway planning regarding the importance of specific movement routes and movement distances

Effectiveness of small road tunnels and fences in reducing amphibian roadkill and barrier effects at retrofitted roads in Sweden.

Schemes to reduce road impacts on amphibians have been implemented for decades in Europe, yet, several aspects on the effectiveness of such schemes remain poorly understood. Particularly in northern Europe, including Sweden, there is a lack of available information on road mitigation for amphibians, which is hampering implementation progress and cost-effectiveness analyses of mitigation options. Here, we present data derived from systematic counts of amphibians during spring migration at three previous hot-spots for amphibian roadkill in Sweden, where amphibian tunnels with guiding fences have been installed. We used the data in combination with a risk model to estimate the number of roadkills and successful crossings before vs. after mitigation and mitigated vs. adjacent non-mitigated road sections. In mitigated road sections, the estimated number of amphibians killed or at risk of being killed by car traffic decreased by 85-100% and the estimated number successfully crossing the road increased by 25-340%. Data, however, suggested fence-end effects that may moderate the reduction in roadkill. We discuss possible explanations for the observed differences between sites and construction types, and implications for amphibian conservation. We show how effectiveness estimates can be used for prioritizing amphibian passages along the existing road network. Finally, we emphasize the importance of careful monitoring of amphibian roadkill and successful crossings before and after amphibian passages are constructed

Predicted impacts of transport infrastructure and traffic on bird conservation in Swedish Special Protection Areas

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The SLOSS dilemma of road ecology: Are several small wildlife crossing structures better than a single large?

Crossing structures for large wildlife are increasingly being constructed at major roads and railways in many countries, and current guidelines for wildlife mitigation at linear infrastructures tend to advocate for large crossing structures sited at major movement corridors for the target species. The concept of movement corridors has however been challenged, and pinching animal movements into bottlenecks entail risks. In this paper, I address the SLOSS dilemma of road ecology, i.e., the discussion whether a Single Large Or Several Small crossing structures along a linear barrier would produce the most benefit for wildlife. I point out risks, ecological as well as practical, with investing in one large crossing structure, and list a number of situations where it may be more beneficial to distribute the conservation efforts in the landscape by constructing several smaller crossing structures; for example when the ecological knowledge is insufficient, when animal interactions are expected to be significant, when the landscape changes over time, or when future human development cannot be controlled. I argue that such situations are often what infrastructure planning faces, and that the default strategy therefore should be to distribute rather than to concentrate passage opportunities along major transport infrastructures. I suggest that distributing passage opportunities over several smaller crossing structures would convey a risk diversification, and that this strategy could facilitate the planning of wildlife mitigation. What to choose would however depend on, i.a., landscape composition and ecology, and on relationships among target species. A single large should be selected where it is likely that it can serve a large proportion of target animals, and where the long-term functionality of the crossing structure can be guaranteed. I illustrate how species and regional differences may influence the choice, using the case of ungulates in Sweden. New research is needed to support trade-offs between size and number of crossing structures. Cost-effectiveness analyses of wildlife crossing structures are currently rare and need to be further explored. Camera trapping and video surveillance of crossing structures provide opportunities to analyze details concerning, for example, any individual biases according to sex, age, status and grouping, and any antagonism between species and individuals. Wildlife ecology research need to better address questions posed by road and railway planning regarding the importance of specific movement routes and movement distances

Greener transport infrastructure – IENE 2014 International Conference

no abstract provided for this editoria

Pine Marten Red Fox interactions – a case of intraguild predation.

We pursued the hypothesis that pine martens (Martes martes L) suffer from intraguild predation by red foxes (Vulpes vulpes L). An increase in population density of pine martens in Scandinavia was observed concominant with a decline in the number of foxes due to an epizootic of sarcoptic mange during the 1980's. The increase was noted both as numbers of crossing marten tracks on snow along transects in a lokal area, and as numbers of martens harvested in Sweden. The latter could be linked county-wise by timing and amplitude to the ocurrence of mange and decline of number in foxes harvested. We also compiled 16 cases of casually observed predation by red foxes on martens, and calculated a yearly mortality rate due to fox predation of 0,13 from>14 transmitter years of 26 collared martens in three areas of Scandinavia during the period of high marten numbers. We conclude that the case against the fox is strong.publishedVersio