Research Article |
Corresponding author: Milla Niemi ( milla.niemi@helsinki.fi ) Academic editor: Andreas Seiler
© 2015 Milla Niemi, Juho Matala, Markus Melin, Visa Eronen, Hannu Järvenpää.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Niemi M, Matala J, Melin M, Eronen V, Järvenpää H (2015) Traffic mortality of four ungulate species in southern Finland. In: Seiler A, Helldin J-O (Eds) Proceedings of IENE 2014 International Conference on Ecology and Transportation, Malmö, Sweden. Nature Conservation 11: 13–28. https://doi.org/10.3897/natureconservation.11.4416
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Ungulate–vehicle collisions are intensively studied in many countries. However, limited knowledge exists on how many animals struck actually die due to collisions and whether differences in traffic mortality occur between species living in the same area. In this study, we estimated a kill rate (the proportion of individuals killed/struck) and, in relation to their winter population sizes, the collision and traffic mortality rates for four ungulate species (moose Alces alces, white-tailed deer Odocoileus virginianus, roe deer Capreolus capreolus, and fallow deer Dama dama). We used an unofficial collision register collected between 2001 and 2012 (a total of 12 years) by voluntary hunters from the Hyvinkää Game Management Area (323 km2) located in southern Finland. The population estimates used were based on annual snow track censuses. A total of 497 ungulates were involved in collisions during the study period. Of these, 76% were killed directly or put down afterwards. Roe deer had the highest kill rate; 95% of struck individuals died. White-tailed deer had the highest collision and traffic mortality rates (8.0% and 6.5% of the winter population, respectively), followed by moose (6.5 % and 4.5%), roe deer (3.9% and 3.7%), and fallow deer (3.2% and 2.1%). As we found the collision and traffic mortality rates to be unequal between species, we recommend separately reporting all ungulate species when compiling collision statistics. We additionally suggest that local managers should be aware of ungulate collision and traffic mortality rates in their areas and should use this knowledge when planning annual harvest.
Deer–vehicle collision, moose–vehicle collision, population size, collision rate, traffic mortality rate, game management
Expanding road networks and globally increasing traffic volumes have many negative effects on the environment and animals (e.g.
Ungulate–vehicle collisions (UVCs) are a notable and increasing traffic safety problem in Europe, North America, and Japan, and are therefore intensively studied in many countries (
Several studies have focused on the temporal and/or spatial patterns of UVCs (
Ungulate traffic mortality in relation to their population sizes is known in many countries. For example, the traffic mortality of roe deer (Capreolus capreolus) has varied between 13% and 16%, depending on the country (
Although the relative importance of road kills seems low in many ungulate populations, regional variation could be notable. For Finland,
Finland has three abundant ungulate game species, whose populations are mainly regulated by hunting: the moose, which is spread across the country; the introduced white-tailed deer (Odocoileus virginianus), which has a dense population concentrated in southwestern Finland and the roe deer, which lives in the southern half of the country (second largest distribution) at low densities (see
During the 21st century, the annual country-level harvest for moose, white-tailed deer, and roe deer has varied between 38–76 000, 14–26 000, and 1–4 000 individuals, respectively. Other species are hunted only marginally; the annual hunting bag has varied between 20–130 individuals for wild forest reindeer and 50–200 individuals for fallow deer (
The aim of our study was to estimate the traffic mortality of four ungulate species living in the same area and to discover possible inter-species differences. First, we were interested in how many percent of animals struck actually die due to collisions (later referred to as kill rate). Second, we wanted to investigate how many collisions have occurred in relation to species population sizes (later referred to as collision rate). Finally, we wanted to explore how large a proportion of the populations have died in the collisions (later referred to as traffic mortality rate). We tested the hypotheses that 1) the collision rate is equal for all species and 2) the traffic mortality rate is equal for all species.
The study was conducted in the area of the Hyvinkää Game Management Association (later referred to as Hyvinkää GMA) (Fig.
The map of our study area. The land use map is simplified from CORINE Land Cover 2006 data (Finnish Environment Institute 2009, CLC2006). Country borders: Eurostat.
The area is divided by fenced National Highway 3 (depending on the road section, the traffic volume was approximately 20–30 000 vehicles/day in 2010; Finnish Transport Agency statistics; heavy traffic included), route 130 (running parallel to Highway 3; 3200–3500 vehicles/day) and a railway. These all run south to north, while in the east-west direction the area is limited by Highway number 25 (5–10 000 vehicles/day), which runs through the southern part of the area. Public road density is approximately 0.7 km/km2, with an annual traffic flow approximately 330 millions of kilometers in 2010 (Finnish Transport Agency statistics). There is additionally a dense network of minor roads and forestry tracks. The speed limit on the main roads varies depending on the road section and season, being 100 or 120 km/hour on Highway 3 and 60 or 80 km/hour on the other main roads.
A total of four ungulate species (moose, white-tailed deer, roe deer, and fallow deer) exist in the area of Hyvinkää GMA. All are game animals, i.e. their populations are managed by hunting. The annual maximum hunting quotas for moose, white-tailed deer, and fallow deer are defined and controlled by licenses granted by the Finnish Wildlife Agency. Roe deer harvest is not regulated by the authorities, but hunters have to report their bag (Hunting Act 615/1993, Hunting Decree 666/1993). The number of hunted individuals is thus known for each species.
The population estimate used in our study was based on an annual snow tracking census (
Moose–vehicle accidents are registered at the species-level in the Finnish collision statistics, but crashes with other wild ungulates are treated as deer–vehicle collisions regardless of the species. Because we were interested in exploring the possible inter-species differences, the existing nation-wide collision database was not usable. We instead used a local dataset collected from the Hyvinkää GMA area by voluntary hunters who work as official assistants to the police.
UVCs in Finland have to be reported to the police, but the crash sites are usually visited by the police only in cases where personal injuries or damage to the vehicle has occurred. The collision sites are instead checked by local hunters, who work as an executive assistance to the police. These volunteers visit every UVC site, put the involved animal down if needed, and transport the carcass away from the road area. The volunteers do not have any registering duties, but will sometimes collect unofficial statistics for their own interests.
For our study, we used a specific UVC dataset collected by voluntary hunters and maintained by the chief of the Hyvinkää GMA. This register contained detailed information concerning e.g. the species and post-collision condition of an animal. The register contained UVCs from between 2001 and 2012 (12 years in total).
From the data collected by the voluntary hunters, we calculated a kill rate, a collision rate, and a traffic mortality rate for each species. The kill rate was simply calculated from the animals struck (how many percent of animals struck died in the collision or were fatally injured and put down afterwards). The collision rate was calculated by combining the collision data and the results of an annual snow census (i.e. how many collisions occur for each 100 individuals assessed in the snow census). The traffic mortality rate was also based on the collision and snow census data (how many individuals died in collisions for each 100 individuals assessed in the snow census). We have converted our results to percentages (e.g. a calculated rate of 0.05 = 5%) to simplify the text.
We used Fisher’s exact test (e.g.
A total of 497 ungulates were involved in 493 collisions during the 12-year study period (Table
Road-killed and struck but uninjured ungulates in the Hyvinkää GMA between 2001 and 2012 (a total of 12 years). Column “Condition unknown” contains animals that have disappeared from the collision site and have not been found later by tracking, and animals whose condition has not been recorded in the database used.
Road-killed individuals | Uninjured individuals | Condition unknown | Total number of individuals struck | |
---|---|---|---|---|
White-tailed deer | 198 (80%) | 4 (2%) | 46 (19%) | 248 (50% of all) |
Moose | 82 (69%) | 12 (10%) | 24 (20%) | 118 (24%) |
Roe deer | 72 (95%) | 1 (1%) | 3 (4%) | 76 (15%) |
Fallow deer | 26 (65%) | 1 (3%) | 13 (33%) | 40 (8%) |
Unknown | 0 (0%) | 1 (7%) | 14 (93%) | 15 (3%) |
Total | 378 (76%) | 19 (4%) | 100 (20%) | 497 (100%) |
A total of 378 individuals (76%) were killed directly in the collisions or put down afterwards (later referred to as road-killed) (Table
In comparison to population estimates derived from the snow track census data, white-tailed deer had the highest collision rate: 8.0% (8.0 collisions/100 individuals), followed by moose (6.5%), roe deer (3.9%), and fallow deer (3.2%) (Fig.
Annual variation in collision and traffic mortality rates for four ungulate species in the Hyvinkää GMA between 2001 and 2012 (a total of 12 years).
The results of the pairwise comparisons between species’ collision rates in the Hyvinkää GMA between 2001 and 2012 (a total of 12 years). Comparisons were made by using Fisher’s exact test and p-values were adjusted using the Bonferroni correction.
Species 1 | Species 2 | DF | p-value |
---|---|---|---|
White-tailed deer | Moose | 1 | 0.048 |
White-tailed deer | Roe deer | 1 | <0.001 |
White-tailed deer | Fallow deer | 1 | <0.001 |
Moose | Roe deer | 1 | <0.001 |
Moose | Fallow deer | 1 | <0.001 |
Roe deer | Fallow deer | 1 | 0.332 |
When analyzing road-killed individuals only (i.e. excluding animals that had disappeared after the collision or were found uninjured), it became apparent that white-tailed deer had the highest traffic mortality rate (6.5% or 6.5 road-killed individuals/100 individuals) followed by moose (4.5%), roe deer (3.7%), and fallow deer (2.1%) (Fig.
The results of the pairwise comparisons between species’ traffic mortality rates in the Hyvinkää GMA between 2001 and 2012 (a total of 12 years). Comparisons were made using Fisher’s exact test and p-values were adjusted using the Bonferroni correction.
Species 1 | Species 2 | DF | p-value |
---|---|---|---|
White-tailed deer | Moose | 1 | 0.003 |
White-tailed deer | Roe deer | 1 | <0.001 |
White-tailed deer | Fallow deer | 1 | <0.001 |
Moose | Roe deer | 1 | 0.249 |
Moose | Fallow deer | 1 | <0.001 |
Roe deer | Fallow deer | 1 | 0.008 |
We calculated the ratio between road-killed individuals and the annual harvest for each species. The proportion of road-killed white-tailed deer was 10.3% of the annual hunting bag. The same proportions for moose, roe deer, and fallow deer were 6.9%, 30.9%, and 49.1%, respectively.
UVCs, especially deer–vehicle collisions, are relatively rarely fatal for humans. The opposite is true for animals. In our data, the smallest species, roe deer, was the most vulnerable: 95% of crashes lead to the death of the animal. This percentage is almost the same (94%) as that found by
Although the size of the struck animal seemed to be an important factor affecting its possibility of surviving a collision, it is not necessarily the only one. Vehicle speed is the most important single variable that is connected to the severity of ungulate–vehicle collisions from the human point of view (
White-tailed deer had the highest collision and traffic mortality rates: eight out of one hundred animals (in the wintering population) were involved in collisions, and the traffic mortality rate was 6.5% of the population.
However, a straight comparison between collision or traffic mortality rates from different areas without knowledge of other explanatory factors does not necessarily illustrate the whole picture. The actual amount of collisions, and hence the amount of road-killed animals, is affected by several factors. Population size is one of the important variables explaining the number of UVCs (
In this study, we were interested in the differences concerning collision and traffic mortality rates between species concurrently living in the same area. The traffic flow and environmental variables were thus same for all species, giving us the possibility of discussing and comparing species behavior-related factors.
We found white-tailed deer to have the highest collision and traffic mortality rates, followed by the moose. However, after calculating Bonferroni corrections for p-values, the statistical difference between species collision rates disappeared while difference between species traffic mortality rates remained. This is likely to be due to the smaller body size of white-tailed deer, and further to the larger road kill rate found in our study. Comparing this species pair in a more detailed fashion would be interesting in the future, to investigate whether their collision rates really differ. Moose are known to have large home ranges and some of the animals implement seasonal migratory behavior (
In our study, roe deer and fallow deer had the lowest collision and traffic mortality rates. This could be connected with the movement behavior of these animals. Studies conducted in southern Finland found the monthly home ranges to be smaller and the daily movement distances shorter for roe deer compared to white-tailed deer (
Ungulate–vehicle collisions cannot happen without an animal being on the road, but the temporal peak of the road crossing rate of animals and the timing of collisions are not necessarily the same.
We found notable inter-species differences when comparing the number of road-killed ungulates in relation to the annual hunting bag. The proportions of road-killed animals for the relatively abundant white-tailed deer and moose were 10.3% and 6.9% of the annual harvest, respectively. For moose, this was comparable with the ratio found in Sweden (
For fallow deer, the number of road-killed individuals was almost as high as the annual harvest. Although the data size was small and strong conclusions should therefore be avoided, our observation implicates the importance of taking species-specific traffic mortality into account when planning harvest quotas. Because the Finnish nation-wide collision register does not differentiate between deer species, local-scale managers could benefit from their own, unofficial collision statistics.
Contrastingly to the relatively low traffic mortality rate (3.7%) of the roe deer, the species’ traffic mortality in relation to the hunting bag (30.9%) was high. Roe deer hunting in Finland is free of licenses, leaving more management responsibility to local hunting clubs and even individual hunters. The past decade has been somewhat difficult for roe deer in southern Finland; the increasing Eurasian lynx (Lynx lynx) population and several severe winters have inhibited the population increase that began approximately two decades ago. It seems that hunters have tried to react to the changing situation by reducing their game bag; the annual amount of hunted roe deer compared to the estimated population size has decreased during the last few years in our study area (
In our paper, we compared the collision statistics of four ungulate species (moose, white-tailed deer, roe deer, and fallow deer) living in the same area. Our main finding shows that both the collision (collisions in relation to population size) and traffic mortality rates (animals killed in collisions in relation to population size) of these four ungulate species differed. White-tailed deer and moose suffered the highest collision and traffic mortality rates. These rates were relatively low for roe deer and especially for fallow deer, although no strong conclusions could be drawn because of the limited amount of data especially in the case of fallow deer.
We were only able to show that the species-specific collision and mortality rates differed, but were unable to evaluate the actual reasons behind our findings. Additional work is thus needed to investigate, which factors affect the amount of collisions, and further, how traffic mortality affects ungulate populations.
However, we believe that managers responsible for defining the hunting quotas could use our results as a tool when planning the management of different ungulate species. We additionally wished to point out that combining several species under the same category in collision statistics may lead to loss of information and should therefore be avoided. Thus, in cases where the official collision register does not contain species-specific information or does not exist at all, local managers may benefit from a detailed collision registering system such as the one used in our study area.
We warmly thank Andreas Seiler and Christer Rolandsen for presenting valuable comments considering the first version of our manuscript and Stella Thompson for correcting our language mistakes. The work of the first author was funded by the Finnish Cultural Foundation and the Finnish Society of Forest Science, which is highly respected. Finally, we wish to present our effusive compliments to the voluntary hunters from the Hyvinkää GMA who collected the data we used, and who are continuing their valuable work.
Annual trends in population size and collisions
Data type: species data
Explanation note: Annual trends in population size, harvest, and collisions.
Contingency tables used in the analysis of collision and traffic mortality rates
Data type: species data
Explanation note: Contingency tables.