Lutra 48(2)_van Vuurde & van der Grift_2005
The effects of landscape attributes on the use of small wildlife underpasses by weasel (Mustela nivalis) and stoat (Mustela erminea)
Increasingly wildlife overpasses and underpasses are being constructed along roads and railroads to mitigate against their barrier effect and to restore habitat connectivity. Surveys show that such wildlife crossing structures are used by a variety of mammal species, including weasel (Mustela nivalis) and stoat (Mustela erminea). Little is known, however, about which attributes of wildlife crossing structures and the surrounding landscape affect their acceptance, and use, by small mustelids. We studied the effect of landscape variables on the crossing rates of small mustelids in 14 small wildlife underpasses along a four-track railroad between the cities of Boxtel and Eindhoven, The Netherlands. Track-plates were used to record animal crossings over a period of eight weeks. We studied three landscape variables: distance to the nearest natural element providing cover (>1.5 m high), distance to the nearest building, and distance to the nearest road parallel to the railroad. Passage length and openness, percentage of the passage length with grates on top, and average number of crossings by animals that predate on small mustelids were studied as co-variables. Small mustelids were found to use 11 underpasses, making a total of 146 crossings (~15% of all animal crossings). We found a significant negative correlation between the crossing rates of small mustelids and the distance to natural cover, while there was an indication of a positive correlation with the distance to buildings. No correlation was found with the distance to the nearest parallel road, the crossing rates by predators, or any of the structural variables of the wildlife underpasses. A correlation with structural variables was not expected, as the selection of underpasses had aimed to minimise such differences. For future research on the identification of variables that affect crossing structure performance we recommend including population density estimations, individual animal movements, the effects of fences on crossing rates, the importance of underpasses for animals on dispersal, and experimental modification of landscape variables around underpasses.