Human Disturbances Force Animals to Move 70% Farther to Survive

Animals move around a lot but with human activity, the distance increases – or decreases – significantly.

River Otter On Log
River otters have larger home ranges in areas polluted by an oil spill. mlorenzphotography / Getty Images

Researchers have long known that human activity has had an impact on animal habitat. When humans move, animals have to move too.

But new research actually calculates the amount of movement, finding that human activity forces animals to move on average 70% farther in order to survive.

Human activities such as logging, agriculture, and urbanization often affect animal habitats, forcing them to find new food, shelter, and to avoid predators. But it’s not just these long-term changes that affect animal movement. Events like hunting and recreation can prompt even larger changes in animal behavior, researchers found.

In the study, published in the journal Nature Ecology & Evolution, scientists wanted to quantify the impact humans have on other animal species.

“Movement is critical to the survival of animals because it allows them to find food, mates and shelter, and escape predators and threats,” lead author Tim Doherty, a wildlife ecologist at the University of Sydney, tells Treehugger.

“We were motivated to conduct this study because the impacts of humans on animal behaviour often go overlooked, but can have serious consequences for wildlife health and populations.”

Animals on the Move

For their research, Doherty and his colleagues analyzed 208 studies on 167 species spanning nearly four decades to determine how human disturbances influence animal movement.

The study roundup included birds, mammals, reptiles, amphibians, fish, and insects. Animals ranged in size from the sleepy orange butterfly at just .05 grams to the great white shark weighing 2,000-kilogram (4,400 pounds).

“We recorded large increases and decreases in animal movement across a wide range of disturbances, including logging, urbanisation, agriculture, pollution, hunting, recreation and tourism, amongst others,” Doherty explains.

They found that human disturbances had widespread impacts on animal movements. And episodic activities such as hunting, recreation, and aircraft use can cause even greater increases in movement distances than activities that change habitat, like logging or agriculture.

These episodic events cause a 35% change in how much an animal moves, including increases and decreases. (Sometimes animals decrease their movement, for example if fences stop how far they can travel.) Habitat-modification activities force a 12% change.

“When we looked at changes in animal movement distances (how far do they move in say an hour or a day), we found that human activities (e.g. hunting, tourism, recreation) caused larger increases in movement than did habitat modification (e.g. urbanisation, logging),” Doherty explains.

“We think this might be because those human activities are episodic and unpredictable in nature, meaning that animals may be more likely to flee longer distances in search of shelter. This does not diminish the importance of habitat modification though because changes in habitat can also have large impacts on animal movement.”

How Animals React

Animals don’t all respond in the same way to human disturbances. Depending on the animal and the activity, they may either increase, decrease, or show no change in their movement, Doherty says.

“For instance, we found that moose in Norway increased their hourly movement distances in response to military activities, whereas northern bearded saki monkeys in Brazil had smaller home ranges in fragmented forests,” he says.

They also found that squirrel gliders living near roads and residential areas in Brisbane, Australia, had smaller home ranges than those living in bushland or the interior.

Noise from petroleum exploration caused increases in movement speed for caribou in Canada. River otters had larger home ranges in areas polluted by an oil spill in the U.S. compared to those outside those locations.

“Increases in movement may occur if animals search over larger areas for food or shelter, or they are running away from threats. Decreases in movement may occur if animals encounter barriers such as roads or farmland, or if food availability is higher (e.g. in many urban areas).” 

Researchers hope that these findings can be used to protect wildlife.

“In terms of policy and management, our work supports calls for avoiding further habitat destruction and degradation, creating and managing protected areas, restoring habitat, and better managing human activities such as hunting, tourism and recreation,” Doherty says.

View Article Sources
  1. Doherty, Tim S., et al. "Human Disturbance Causes Widespread Disruption of Animal Movement." Nature Ecology & Evolution, 2021, doi:10.1038/s41559-020-01380-1

  2. "Human activity forces animals to move 70 percent further to survive." The University of Sydney, 2021.