Oh Deer! Using fear to mitigate inflated herbivore populations in urban areas

What Africa can teach us about handling our deer problem 

Living in the Maritimes, you have likely noticed just how many deer are around the towns, along roadsides, and filling up some farmer’s fields. The high populations of deer around human settlements are most likely the result of the absence of large predators. As human landscapes expand into previously wild habitats, predators, like wolves, bears, and cougars, are often the first species to get pushed out. Humans drive them away because they can be a danger to our livestock and pets, but we often do not consider the effects this could have on the local ecosystems and our communities.

 

Across the ocean, in Mozambique’s Gorongosa National Park, a similar issue is taking place. After the civil war ended in 1992, the park was left with no large predators like leopards or African wild dogs. The absence of these predators means that the herbivores are now living in a landscape devoid of fear, and this has emboldened them to begin exploring new areas and drastically inflating their numbers. For example, a species of forest-dwelling antelope, called bushbucks, left their native woodland habitat in the park and moved onto the floodplains.

 

Bushbucks, as their name implies, rely on forest cover to be safe from predators. But with no predators present, there was no motivation for them to stay confined to the forest. So, they moved out and into the open floodplains and began eating new foods. This novel diet consisted of waterwort, a common food staple for floodplain grazers. However, scientists noted that the influx of bushbucks was causing the amount of waterwort to dwindle to the point that other species were having trouble finding enough to eat.

 

A team of researchers, led by Dr. Robert Pringle of Princeton University, decided to reintroduce fear into this ecosystem in the hopes of getting the bushbuck to move back into the forests and allow the waterwort to regrow. To reintroduce fear, the scientists played leopard vocalizations, placed artificial lion scat, and sprayed a generic carnivore urine. Very quickly, they observed bushbuck moving back to treed areas.

In recent years, there has been increased interest among ecologists about how fear plays a role in the balancing of ecosystems. This study can have much larger implications for managing herbivore populations around the world, including right here in the Maritimes.

 

Multiple studies have found that reintroducing fear into landscapes devoid of large predators can help rebalance ecosystems that have been taken over by herbivores or small-bodied carnivores. One such study was conducted by Dr. Justin Suraci, during his PhD at the University of Victoria. Suraci found that the sound of barking dogs instilled fear into inflated racoon populations ravaging the British Columbia coast, which led to prey species, like crabs, fish, and songbirds, rebounding when the sound of predators were present—mirroring Pringle’s bushbuck findings.

 

“Large carnivores…can in some cases play a critical role in structuring ecosystems by suppressing their prey,” says Suraci, and those large carnivores “can have these trophic effects across food chains just through the fear they induce in their prey.” This is an important area of study because it could solve many of the issues we are seeing in the Maritimes today with dense populations of deer being well-known for raiding farmers’ crops and people’s gardens.

 

The lack of predators around Sackville, and across much of the Maritimes, has caused an explosion in the deer population. This is perhaps best exemplified by what is being seen in the town of Truro, Nova Scotia. Lauren Farrell, a student at Mt. A and resident of Truro, said that, “the most noticeable issue that has come with the huge deer population in Truro is collisions on the road.” Farrell notes that, “there is an active effort to cull the deer population…[by] letting hunters with crossbows hunt deer within town limits.” While culling is certainly an effective solution, listening to scientists like Suraci, who have studied how fear can influence nuisance wildlife, can give us another angle to solve the problem.

 

“There is a growing interest in harnessing the ecology of fear to manipulate wildlife behaviour,” says Suraci, and that by designing well thought out procedures, “cues of predators or threatening competitors (e.g., sounds, scents, etc.) can conceivably be used to deter native ‘pests’ from sensitive environments.”

 

We may well have another instrument in our management toolbox that can help us try to bring balance to Maritime deer numbers. By harnessing their natural fear response, we could have a simple and effective way to mitigate the damage that their dense populations can have on crops, gardens, and greenspace, as well as reducing the likelihood of vehicle collisions. We just have to find the right way to put the fear of ‘dog’ into them.

 

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