Inside:  How roads impact wildlife is a growing concern of many municipalities and is the main focus of road ecology.  Roads change the environment in some way and most of these changes are bad news for the local wildlife.

How roads impact wildlife is the main concern of road ecology. There are many ways roads impact wildlife. Ever since humans started travelling, there have been roads.  Initially, I guess, they would have been called trails.  Regardless, these trails would have seen foot traffic, horse and rider traffic and eventually horse drawn wagons.  All of these changed the environment in some way as they passed through the landscape.  And, these changes would have affected the well-being of the local wildlife.

Horse and buggy on a trail

Even horse and buggy affect how roads impact wildlife.
Image by Tomasz Proszek from Pixabay

After the invention of the car and the gradual movement of people to the suburbs, roads began to criss-cross the environment connecting cities large and small.

Map of criss-crossing roadways.

Cars and movement to suburban living greatly affected how roads impact wildlife.
Image by Lorenzo Cafaro from Pixabay

Impacts of roads on wildlife can be split into 3 main categories:

  1. causing direct death
  2. shifting population dynamics
  3. a source of pollution

How Roads Impact Wildlife – Direct Death

Why did the chicken cross the road?  Hard question to answer but here’s a tragic story.  One day one of the chickens on our farm did cross the road.  On her way back home a stray dog ran after her, caught her midway across and both were hit by a car just as the poor dog snapped his jaw shut on our poor girl.  No one claimed the poor dog and both animals joined our pet cemetery.

Cars drive quickly on our country road.  I have seen dead squirrels (many raised on my farm feeding on my bird feeders) and racoons.  Bunnies and feral cats have often been the victims of road death on our road as well.

Animals are often killed when they cross the road.  In the United States, over 400 million animals are killed yearly by drivers.  In Ontario, Canada alone there are an estimated 14,000 wildlife-vehicle collisions a year. And often, it is not only the wildlife that are killed as human death often is a result of these collisions.

Dead squirrel on a road.

Squirrels are often victims of cars on roads.
Image by Epic Images from Pixabay

Factors Influencing Why Wildlife are Killed on Roads

How roads impact wildlife is the key focus of road ecology and that impact very often involves death of an animal. How many animals get killed on roads is influenced by many factors:

  • when a road crosses an animal’s favorite habitat, the chance of being hit by a car rises greatly
  • some animals have behaviors that put them more at risk
    • eg. insect eating birds are often killed when they fly close to the ground chasing insects
  • animals that are part of regular mass migrations like amphibians are very prone to road mortality
  • some animals have natural defense mechanisms that make them more likely to be victims of road death
    • turtles afraid of cars will draw into their shells and stay on the road making them more likely to be killed
    • snakes often ‘freeze’ in fear when cars approach
  • movement patterns of animals can increase their contact with roads making them more likely to be involved in a collision
    • animals with a large home range like cougars and moose have a better chance of encountering roads
    • some animals travel greater than normal distances during certain life stages like when finding a mate (some snake species) or laying eggs (many terrestrial turtles) resulting in them crossing roads or coming too near roadways
Turtle on a road

Turtle on a road is likely to be killed.
Image by giorgos250 from Pixabay

Changing Population Dynamics Due to Roads

Roads criss-crossing the countryside tend to split the land into small pieces also known as habitat fragmentation.  This fact along with road mortality often targeting certain parts of a wildlife population results in serious changes to wildlife population profiles:

  • from May to September, female turtles are killed in larger numbers than males either because they cross roads to get to nesting sites or lay eggs on sandy road sides which changes the ratio of males to females in the population
  • baby puffins attracted to city lights find themselves on roads and are killed in large numbers which changes the age structure of this population
  • habitat fragmentation affects population structures by increasing road kill or by reducing mixing of these ‘island’ populations when individual animals avoid crossing roads at all
  • when animals avoid crossing roads, gene flow between these ‘island’ populations becomes restricted and this reduces genetic diversity
    • some animals like snakes follow pheromone trails to find mates and roads can disrupt these trails meaning fewer snakes will find mates
    • roads can prevent female turtles from reaching their preferred nesting sites so eggs are laid in poorer habitat meaning fewer baby turtles will hatch
  • fragmented forests see new edge habitat that has different conditions than the forest interior
    • nesting birds get preyed on more easily along edge habitat changing their population structure
    • roadsides are often ideal nesting sites but make adult turtles and hatchlings more prone to death and predation
Roads through a forest create new edge habitat.

Roads through a forest create new edge habitat.
Image by Markus Distelrath from Pixabay

Roads are a Source of Pollution

Roads contribute many kinds of pollutants into the environment.  Chemicals are an obvious pollutant type but light and noise pollution also cause problems.

Toxic Pollutants from Vehicles

Cars spew toxins from internal combustion.  These toxins can kill wildlife outright or cause physical or behavioural alterations that reduce fitness and change population dynamics:

  • deicing salts that make their way into nearby ponds can increase the death rate of wood frogs and spotted salamanders
  • these same deicing salts can also change frog behavior and make their movements more awkward; thus, frog fitness can be lowered because they catch fewer prey and/or get caught more often by predators
  • frogs that live near roads have more skeleton defects
  • oil from cars is a dangerous toxin that harms living things when it enters the environment

Light and Noise Pollution from Roads

Light plays an important role in the behavior of many animals:

  • some birds like robins are stimulated to sing when its sunny; light from cars can make robins sing at night
  • road and house lights can throw baby puffins off course and cause them to fly towards roads where they are often hit by cars
  • mating of fireflies is also affected as many species use specific flashing patterns to attract mates; “Scientists have observed that synchronous fireflies get out of synch for
    a few minutes after a car’s headlights pass.” –
Robin singing during the day.

Daylight stimulates many birds to sing.
Image by cocoparisienne from Pixabay

Many animals communicate acoustically.  Noise from cars can interfere with animals communicating with each other:

Croaking frog.

Street noise can interfere with frog calls making finding mates harder.
Image by 4924546 from Pixabay

Roads have many affects on wildlife and most of them are harmful.  They cause outright death through car impacts.  Population dynamics are often affected by the fragmentation of habitat caused by roads.  And finally, they are a source of pollution that leads to declines in many wildlife populations from toxins as well as through noise and light pollution.  How roads impact wildlife is a main focus of road ecology.  These negative impacts are the reason road ecology principles need to be included in the planning practices of all municipalities.