Can we know the distribution and abundance of wildlife from the data on animals run over on roads?

    A new analytical approach makes it possible to obtain maps of the distribution and abundance of two species of ungulates, the roe deer and the wild boar, from the road kills of these animals, controlling for the effects that factors such as road density or the season of rain may have. year on predictions.


    Knowing how many animals there are and what their distribution is is key when it comes to managing wildlife populations, for example, for the conservation of threatened species or for the control of zoonotic diseases. However, this information is not easy to obtain on a large scale, since the cost of specialized methodologies for the monitoring of fauna, such as the camera trapping or the tracking of individuals by means of GPS, is too high to be able to be applied in large extensions of territory.

    Scientists from the Instituto de Investigación en Recursos Cinegéticos (IREC – CSIC, UCLM, JCCM) have taken advantage of the information generated from outrages of Roe deer (Capreolus capreolus) y wild boar (Sus scrofa) to generate abundance maps of these two species in mainland Spain. The study used the Royle–Nichols hierarchical modeling approach to control for the possible effect that factors such as road density or time of year might have on the distribution and number of accidents.

     

    The roads have become deadly traps for many animals that, like wild ungulates, try to cross them or feed in their ditches, creating a risk of collision with passing vehicles.

    The study was carried out from the collisions with these two species that generated a report during the year 2017. To model the abundance of these ungulates, variables related to climate and vegetation cover were taken into account, while variables such as road density or road density were included to control the effect of traffic intensity or vehicle speed. the type of road (urban layout, conventional roads or dual carriageways).

    In addition, the temporal pattern of the accidents was studied to consider the heterogeneity that could exist both in the activity of the species and in the number of vehicles present on the roads throughout the year. He The abundance index obtained was evaluated at the provincial level by comparing it with the hunting bags of these animals., another metric commonly used as a large-scale index of abundance.

     

    Data and results of the study for wild boar. A) Abundance index for wild boar from roadkill data. B) Detectability estimated by the model (“bias control” in the data on road accidents). C) Wild boar run over in 2017 used in the study. D) Correlation between the abundance index obtained from the road kill data and the hunting bags at the provincial level.

    The results, published in the journal ultrasound, have shown that it is possible to obtain abundance maps of roe deer and wild boar from road kill data when controlling for biases derived from factors such as traffic intensity or animal activity. Collisions with wild boar occurred mainly between the months of October and December, while run over by roe deer were more common between the months of April and July.

    In addition, the results allowed to identify "future blackheads”, that is to say, areas in which, without the species being present today, could constitute a problem in the future both for the safety of drivers and for the survival of animal populations.

    The study also found that a greater number of road kills does not always equate to a greater abundance of animals, as occurs with the wild boar in the central areas of Castilla y León. This reflects the dual origin of the "hit and run data", in which two factors necessarily come together: that there are animals and that there are vehicles. Therefore, a high rate of collisions may also be due to a greater number of vehicles or other variables, such as their higher speed.

     

    Collision probability with a wild boar (A) and with a roe deer (B) according to the month of the year in mainland Spain.

    This research shows that It is possible to take advantage of the information contained in wildlife road kills to study the distribution and abundance of species on a large scale.. In addition, the generation of maps of abundance and the risk of collision with wild animals opens the door to the future development of tools and technologies that can be used both for the management of threatened animal populations and to mitigate the risks in the safety of drivers.

    The scientific publication of this research is available at: