SCHREVEN KHT & VAN DER HORST YHTH (2022) The road takes its toll: traffic victims in relation to characteristics of species, environment and a fauna passage. LIMOSA 95 (1): 3-27.
Monitoring traffic victims has lost popularity among
naturalists but is still needed to assess current toll of traffic
on animal populations. We monitored traffic victims on the
Nijmeegsebaan, a 4.5 km provincial road in a mixed forest
between Groesbeek and Nijmegen, eastern Netherlands.
Between 2007 and 2017 this transect was surveyed by bike,
on average daily. We found 508 traffic victims of 51 species
(birds: 280 resp. 30, mammals: 167 resp. 16, amphibians: 59
resp. 4, reptiles: 2 resp. 1), i.e. 12.0 victims per km per year.
Birds were mostly found on transects with open canopy
cover, adjacent to a more open landscape including
gardens, and where road verges were below road level
(i.e. twice as many as where verges were at or above road
level). Mammals were mostly found where the forest edge
ran perpendicular to the road, and close to built-up areas in
the forest. Amphibians were mostly found beside (far) forest
ponds. Traffic victim numbers peaked in spring and autumn
for all taxa. However, patterns varied interspecifically and
our monitoring frequency was lower during summer.
For Blackbirds, Great Tits and Blue Tits, juveniles peaked
in May-June. Blackbirds in their second calendar year or
older showed a strong male bias in early spring. Local
abundance explained 33% of variation in the number of
traffic victims per bird species. After correcting for local
abundance, bird species occupying the forest canopy were
killed less frequently than species living in the undergrowth.
Mitigation measures (1m high fences and a tunnel) added in
2012 along part of the road decreased the number of killed
amphibians, but the effect on other taxa was not significant.
Our calculated annual mortality per km in forest was lower
than what was found in the Netherlands in 1957-76, for
Blackbirds also relative to their local abundance. Possibly
Blackbirds have adjusted their road crossing frequency or
behaviour. We suggest that increasing road verge elevation,
which may increase the flight height of birds crossing the
road, could spare traffic victims among birds, a group for
which currently few mitigating measures are in use.
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