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No. 312: Mammals use of larger fauna passages in Vendsyssel

Elmeros, M. & Hansen, T.S. 2019. Pattedyrs brug af større faunapassager i Vendsyssel. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 54 s. - Videnskabelig rapport nr. 312.


Roads fragment wildlife populations and restrict wildlife’s ability to disperse and utilize habitats and resources in the landscape. To reduce the negative impact of roads on wildlife populations, fauna passages are constructed on major roads. Fauna passages defragments the landscape and increase the connectivity between natural habitats for wildlife. Wildlife use of fauna passages may change temporally due to changes in human land-use near the passages, changes in population sizes in the region, changes in factors related to the passages, access, etc.

Two motorways were constructed in the period 1996-2004 in Vendsyssel in northern Denmark. Several fauna passages were build at the motorways to minimize the motorways impact on the wildlife. Mammals’ use of eleven fauna passages were monitored for twelve months in 2005-2006. In 2017-2018, we repeated the study at seven of the largest passages that were constructed to enable large and medium-sized mammals to cross the motorways (three dry culverts at Dybvad, Sulbæk and Vestbjerg, three under passages at river crossings at Lindholm Å, Ryå and Sæby Å, and an overpass at Jyske Ås).

The objectives for the study in 2017-2018 were 1/ to document which large and medium-sized mammal species that used the passages now and analyse the species’ activity (crossings per day) at the passages in relation to landscape characteristics adjacent to the passages, 2/ to assess the changes in animal use of the passages and changes in population sizes from 2005-2006 to 2017-2018, and 3/ to compare the activity estimates recorded by tracking beds with sand and wildlife cameras. 

The activity of species and species groups were recorded four days per month with the tracking beds. The wildlife cameras were deployed and were active throughout the months from September 2017 to August 2018.

Species’ use of the fauna passages and landscape characteristics

All large and medium sized mammal species that occur in Vendsyssel, were recorded at the fauna passages with wildlife cameras. Overall, the most common species were roe deer (Capreolus capreolus), red fox (Vulpes vulpes) and stone marten (Martes foina). On the fauna bridge at Jyske Ås, there was a very high activity (crossings per day) of fallow deer (Dama dama). Otherwise, fallow deer and red deer (Cervus elaphus) were only recorded sporadically in three of the other passages relatively small underpasses. Red deer and fallow deer were not widely distributed in Vendsyssel when the surveyed motorway and fauna passages were planned.

The activity of red fox was highest at Sulbæk and Jyske Ås, and lowest at Ryå. Eurasian badger (Meles meles) was recorded at all passages in low numbers, but the activity was high at Lindholm Å. Eurasian otter (Lutra lutra) was recorded in all the underpasses, but most regularly in the passages at river crossings. The brown hare (Lepus europaeus) was primarily recorded at Ryå and Søby Å, but only rarely in thee dry culverts. Domestic or feral cats (Felis catus), dog (Canis familiaris) and humans (Homo sapiens) were recorded at all passages. The non-native raccoon dog (Nyctereutes proconoides) and American mink (Neovison vison) were recorded occasionally at some passages.

The landscape characteristics that best explained the variation in activity of large and medium sized mammals on the fauna passages were the area of and distance to forest and arable lands, and the heterogeneity of the landscape. A large forest cover near the fauna passages was related to a high activity of deer sp. and red fox. For roe deer, the activity at fauna passages were also correlated to the heterogeneity of the landscape near the passages. The activity of mammals were generally negatively correlated with the area of arable lands and positively correlated to the distance of arable lands.

There was a huge variation in the activity of species and species groups between the individual fauna passages. Contributing factors to the variation is probably local factors such as e.g. the occurrence of family groups at some passages, the passage is located at the boarder of home-ranges of territorial species, as indicated by latrines in an underpass with high activity of Eurasian badger. Due to the relatively low number of fauna passages that were examined in the study and the short length of the study, the analyses of the relationship between the species’ use of the passages and landscape characteristics is very sensitive to such local variations.

Changes in activity from 2005-2006 to 2017-2018

The tracking beds were used to assess the changes in species activity from 2005-2006 to 2017-2018. The activity of deer sp. was twice as high in 2017-2018 as in 2005-2006, while the activity of large carnivores (red fox, Eurasian badger, Eurasian otter and raccoon dog) and small carnivores (stone marten, polecat (Mustela putorius), stoat (Mustela ermniea) and American mink) had declined 50%.

The increased activity of deer sp. was primarily triggered by a large increase in the activity of fallow deer, especially at the overpass at Jyske Ås. Fallow deer was only recorded sporadically in 2005-2006. The activity of roe deer only increased 67% from 2005-2006 to 2017-2018. In 2005-2006, fallow deer was only recorded sporadically in one underpass, while red deer was not recorded at all.

Red fox activity was 68% lower in 2017-2018 compared to 2005-2006, while the activity of Eurasian badger had doubled. Most of the recorded activity of small carnivores was stone marten. In 2017-2018 the activity of stone marten had declined to 47% of the activity level in 2005-2006. The temporal changes in activity of the different species and species groups varied significantly between the individual fauna passages. Activity of a species could have increased at some passages, while it had declined at other passages.

The temporal changes in activity at the fauna passages for game species was compared to the development in the game bag statistics, which is assumed to reflect changes in the population size over the same period. Overall, the changes in activity levels at the fauna passages from 2005-2006 to 2017-2018 were similar to the development in the species’ game bags. The hunting bags had increased for roe deer (28%), fallow deer (166%), and red deer (212%), while the hunting bags had declined for red fox (19%) and stone marten (27%). However, while the brown hare hunting bag had declined 14%, the overall activity at the fauna passages had increased 43%.

Comparison of methods

Overall, tracking beds recorded a higher activity of deer sp., roe deer, and larger carnivores than the wildlife cameras. However, when analysed on the individual fauna passages, the differences between activity measures were only significant at one of the underpasses. Activity was only recorded with the tracking beds for four days per month, but the cameras recorded activity throughout the month. The cameras recorded more species using the fauna passages per month than the tracking beds. The overall costs of using wildlife cameras to monitor animal use of fauna passages are lower than the costs to monitor the activity with tracking beds, wildlife cameras provides better opportunities to identify species and assess the numbers of individual crossing the fauna passages than track beds.

To assess the effects of human disturbance on the animals’ use of fauna passages, we compared the activity as recorded with the wildlife cameras during the week when the tracking beds were inspected and the following weeks until the next inspection. The activity of deer sp., large carnivores and brown hare at the fauna passages increased in the weeks following inspection of the tracking beds, indicating that the daily activity of humans at the passages decreased the number of animal crossings.

Syntheses and application

  • The fauna passages in Vendsyssel are used by all large and medium-sized mammal species that occur in the region. Thus, the fauna passages contribute to maintain connectivity for wildlife species between habitats and subpopulations that are fragmented by the motorways.
  • The mammals’ use of the fauna passages were positively correlated to the area of forests and landscape heterogeneity in the vicinity of the fauna passages, while the activity is negatively correlated with the area of arable lands around the fauna passages.
  • The overall temporal changes of game species’ (roe deer, fallow deer, red deer, red fox and stone marten) use of the fauna passages were correlated with the changes in species population sizes as indicated by the species’ game bags. However, there is a large variation in temporal trends in the species use between individual fauna passages.
  • Species’ distribution ranges change over time. Road infrastructures including fauna passages should be planned and designed to accommodate species that may occur in the region during the whole planned lifetime of the infrastructure.
  • Wildlife cameras can record animal activity for long periods without disturbing the animals’ use of the fauna passages. Wildlife cameras also provide better possibilities to identify species and numbers of crossings. Therefore, wildlife cameras are recommended for future studies of animals’ use of fauna passages.
  • Human activity at fauna passages reduces their effectiveness. Humans activity should avoided at fauna passages and in their vicinity. Combined use of passages should only be allowed on very vide passages (>50m), and the traffic of humans should be restricted to a fenced track at one side of the passages.