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Vehicles

If you drive a vehicle on a regular basis, chances are you have hit a bird or another wild animal at some point. Of course it wasn’t on purpose, and may have seemed unavoidable, but this form of mortality – vehicle collisions – is responsible for the deaths of more than 13.8 million birds each year according to an Environment Canada Report[1] – representing at least 80 species – across Canada. On a per-kilometer basis, that’s more than 34 birds on average for every kilometer of road in Canada per year. Given the number of vehicles on the road, and the growing density of roads around the outskirts of cities, bird collisions with vehicles are a difficult problem to mitigate but one for which drivers, like it or not, are ultimately in the driver’s seat. While an obvious solution is to drive less, another is to drive at the speed limit which unfortunately many people do not do. Click on our vehicle collisions backgrounder and the other resources below to find out more.

Background

Vehicles-1Vehicle collisions are responsible for the deaths of more than 13.8 million birds each year across Canada, and likely higher numbers of mammals, reptiles and amphibians. At least eighty bird species are impacted by this threat. On average, more than 34 birds fall victim to vehicle collisions for every kilometer of 1- to 4-lane roads in Canada each year. The majority of species affected are songbirds. The next most affected group is owls; in southern British Colombia alone, up to 850 individual owls may fall victim to vehicle collisions annually.  Species at risk are also victims of vehicle collision.   Collision with vehicles is considered one of the contributing factors to the demise of the Endangered Eastern Loggerhead Shrike. At Reed Lake Saskatchewan, local naturalists have reported finding dead Red Knots (an endangered species of shorebird) along the causeway road, on which shorebirds, including Knots can gather during times of high water levels in the spring.

The data on roadkill mortality of birds from across North America confirm that songbirds and owls are the groups most affected by vehicle collisions. Table 1 outlines some of the additional groups of bird species that are impacted by vehicle collisions, both from a continent-wide and a national perspective. It should be noted that the number of Canadian studies available is just on quarter that of comparable American studies and none of the Canadian studies have been done at a national scale.

Table 1 – Proportions of different avian taxonomic groups affected by vehicle collisions in North America (based on 28 studies to-date including 157 affected species; column 1) and Canada (based on 7 studies to-date including 80 affected species; column 2). Data are taken from Table 4 in Bishop & Brogan (2014). Raw numbers of dead birds are listed in parentheses.

Taxonomic order of birds Proportion of all vehicle collision casualties based on all North American studies to-date. Proportion of all vehicle collision casualties based only on Canadian studies to-date.
Songbirds (Passeriformes) 40% (2,465) 65.1% (1,225)
Owls (Strigiformes) 25% (1,539) 3.67% (69)
Shorebirds & allies (Charadriiformes) 4.3% (264) 0.9% (17)
Woodpeckers (Piciformes) 4.2% (255) 0.16% (3)
Nightjars (Caprimulgiformes) 1.9% (117) 0.05% (1)
Grouse, Turkeys, etc (Galliformes) 1.5% (92) 0.69% (13)
Waterfowl (Anseriformes) 0.6% (38) 1.06% (20)
Unidentifiable casualties 18% (1,132) 27% (508)

 

The greatest contributing factors in all of these collisions are:

  • Traffic volume (particularly over 10,000 cars in Annual Average Daily Traffic, or AADT counts[2])
  • Vehicle speed (particularly at and over 60-80 km/hr)
  • Configuration and density of roads (Along waterways; isolating nesting/roosting areas from food; significant crossing distances)
  • Time of year (During migration, courtship, breeding and fledging)
  • Presence of bird habitat and food sources along roadways (Fragmenting breeding, foraging and/or cover habitats)

How and why does this happen?

Birds constantly use airspace to move around, and make millions of road crossing each day in Canada. When habitat that supports birds is adjacent to, or on either side of the road (essentially bisected by the road), crossings can be lethal. Birds cannot judge the speed of oncoming vehicles. The faster the vehicle, the less reaction time a bird has to deviate from its course.

Unlike some of the other significant direct human causes of bird mortality, vehicle collisions seem to be more numerous in rural areas. By combining the last 85 years of data and studies available in the United States and Canada‡ and looking at many of the ecozone types in southern Canada, researchers found that mortalities were highest on roads through rural habitats including wetlands (up to 51 birds/100 km/day), mixed and broadleaf forests (9.1‒26 birds/100 km/day), and cropland (6.8 birds/100 km/day). Roads through coniferous forest habitats were associated with the least vehicle collisions for birds (0.093‒0.41 birds/100 km/day). All things considered, some of the highest bird mortality rates have been reported along low-volume roads in or adjacent to protected areas in Canada, particularly where open water is present. Rural areas usually have higher speed limits, which is likely partly responsible for these higher mortality rates.

Habitat beside roads can be attractive to some types of birds. For example, for ground-feeding birds and those that feed on flying insects, roadsides and ditches can be reliable sources of food. Many birds of prey – including owls, hunt along roadsides and ditches. These areas attract and/or provide suitable habitat for small mammals, large insects like grasshoppers and amphibians like frogs that can live in pooled water in ditches. Road kill itself attracts its own suite of scavengers such as crows and vultures. During winter, some species, particularly finches, larks and buntings, land in large numbers on roads to eat grit and road salt. Sometimes river corridors and other natural habitat features are migration routes for species that migrate during the day. Birds that cross roads to continue in their migration direction are at risk of collision. Disconcertingly, most studies show that adults, not young birds, are more susceptible to roadkill given their roles in finding food, defending territory and attracting mates. However, this factor also leads to high mortality in young birds during nesting season, given that they lose parental care.

It should be noted that Bishop and Brogan’s 2014 first-ever national estimate of avian roadkill in Canada looked only at roads outside of major metropolitan areas that pass through deciduous, coniferous and mixed forests, croplands, treed rangeland, wetlands and nonagricultural landscapes with less than 10% tree-cover. Therefore, estimates of avian roadkill for other habitat types are not yet known. In urban areas, there is some evidence suggesting that Barn Swallows and small owl species may actually be more susceptible to vehicle collisions (Gunson et al 2010).

What can we do?

Simple things we can do to mitigate this problem include:

  • Slowing down on rural roads, especially road sections that bisect wetlands or open water, and especially during the breeding and fledging period between May and August.
  • Driving the speed limit always. Driving the speed limit saves lives but also reducing fuel consumption, saving you money and resulting in lower carbon emissions.
  • Driving defensively. Keeping an eye out for birds or mammals on the roadside in agricultural areas just as you would for people in the city or town.
  • Avoid swerving to avoid a collision. Instead, use horn, slow down, and drive straight.
  • Never stop on the road for a bird or other animal. Instead, pull well over onto the shoulder and never put yourself at risk to save an animal on the road.   Only help shoo it off the road when the coast is 100% clear.

[1] The period used for this estimate is actually just 122-days representing the 4-month courtship, breeding and fledging season for most birds in Canada, which is the peak period for bird mortality associated with vehicle collisions.

 

[2] Reported by Summers et al (2011)

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