Fences have big effects on land and wildlife around the world that are rarely measured

Australia’s dingo fences, built to protect livestock from wild dogs, stretch for thousands of kilometers.
Marian Deschain/Wikimedia, CC BY-SA

Alex McInturff, University of California Santa Barbara; Christine Wilkinson, University of California, Berkeley, and Wenjing Xu, University of California, Berkeley

What is the most common form of human infrastructure in the world? It may well be the fence. Recent estimates suggest that the total length of all fencing around the globe is 10 times greater than the total length of roads. If our planet’s fences were stretched end to end, they would likely bridge the distance from Earth to the Sun multiple times.

On every continent, from cities to rural areas and from ancient to modern times, humans have built fences. But we know almost nothing about their ecological effects. Border fences are often in the news, but other fences are so ubiquitous that they disappear into the landscape, becoming scenery rather than subject.

In a recently published study, our team sought to change this situation by offering a set of findings, frameworks and questions that can form the basis of a new discipline: fence ecology. By compiling studies from ecosystems around the world, our research shows that fences produce a complex range of ecological effects.

Some of them influence small-scale processes like the building of spider webs. Others have much broader effects, such as hastening the collapse of Kenya’s Mara ecosystem. Our findings reveal a world that has been utterly reorganized by a rapidly growing latticework of fences.

Conservationists and scientists have raised concerns about the ecological effects of the U.S.-Mexico border wall, most of which is essentially a fence.

Connecting the dots

If fences seem like an odd thing for ecologists to study, consider that until recently no one thought much about how roads affected the places around them. Then, in a burst of research in the 1990s, scientists showed that roads – which also have been part of human civilization for millennia – had narrow footprints but produced enormous environmental effects.

For example, roads can destroy or fragment habitats that wild species rely on to survive. They also can promote air and water pollution and vehicle collisions with wildlife. This work generated a new scientific discipline, road ecology, that offers unique insights into the startling extent of humanity’s reach.

Our research team became interested in fences by watching animals. In California, Kenya, China and Mongolia, we had all observed animals behaving oddly around fences – gazelles taking long detours around them, for example, or predators following “highways” along fence lines.

We reviewed a large body of academic literature looking for explanations. There were many studies of individual species, but each of them told us only a little on its own. Research had not yet connected the dots between many disparate findings. By linking all these studies together, we uncovered important new discoveries about our fenced world.

Early advertisement for barbed wire fencing, 1880-1889. The advent of barbed wire dramatically changed ranching and land use in the American West by ending the open range system.
Kansas Historical Society, CC BY-ND

Remaking ecosystems

Perhaps the most striking pattern we found was that fences rarely are unambiguously good or bad for an ecosystem. Instead, they have myriad ecological effects that produce winners and losers, helping to dictate the rules of the ecosystems where they occur.

Even “good” fences that are designed to protect threatened species or restore sensitive habitats can still fragment and isolate ecosystems. For example, fences constructed in Botswana to prevent disease transmission between wildlife and livestock have stopped migrating wildebeests in their tracks, producing haunting images of injured and dead animals strewn along fencelines.

Enclosing an area to protect one species may injure or kill others, or create entry pathways for invasive species.

One finding that we believe is critical is that for every winner, fences typically produce multiple losers. As a result, they can create ecological “no man’s lands” where only species and ecosystems with a narrow range of traits can survive and thrive.

Altering regions and continents

Examples from around the world demonstrate fences’ powerful and often unintended consequences. The U.S.-Mexico border wall – most of which fits our definition of a fence – has genetically isolated populations of large mammals such as bighorn sheep, leading to population declines and genetic isolation. It has even had surprising effects on birds, like ferruginous pygmy owls, that fly low to the ground.

Australia’s dingo fences, built to protect livestock from the nation’s iconic canines, are among the world’s longest man-made structures, stretching thousands of kilometers each. These fences have started ecological chain reactions called trophic cascades that have affected an entire continent’s ecology.

The absence of dingoes, a top predator, from one side of the fence means that populations of prey species like kangaroos can explode, causing categorical shifts in plant composition and even depleting the soil of nutrients. On either side of the fence there now are two distinct “ecological universes.”

Our review shows that fences affect ecosystems at every scale, leading to cascades of change that may, in the worst cases, culminate in what some conservation biologists have described as total “ecological meltdown.” But this peril often is overlooked.

The authors assembled a conservative data set of potential fence lines across the U.S. West. They calculated the nearest distance to any given fence to be less than 31 miles (50 kilometers), with a mean of about 2 miles (3.1 kilometers).
McInturff et al,. 2020, CC BY-ND

To demonstrate this point, we looked more closely at the western U.S., which is known for huge open spaces but also is the homeland of barbed wire fencing. Our analysis shows that vast areas viewed by researchers as relatively untrodden by the human footprint are silently entangled in dense networks of fences.

Do less harm

Fences clearly are here to stay. As fence ecology develops into a discipline, its practitioners should consider the complex roles fences play in human social, economic and political systems. Even now, however, there is enough evidence to identify actions that could reduce their harmful impacts.

There are many ways to change fence design and construction without affecting their functionality. For example, in Wyoming and Montana, federal land managers have experimented with wildlife-friendly designs that allow species like pronghorn antelope to pass through fences with fewer obstacles and injuries. This kind of modification shows great promise for wildlife and may produce broader ecological benefits.

Another option is aligning fences along natural ecological boundaries, like watercourses or topographical features. This approach can help minimize their effects on ecosystems at low cost. And land agencies or nonprofit organizations could offer incentives for land owners to remove fences that are derelict and no longer serve a purpose.

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Nonetheless, once a fence is built its effects are long lasting. Even after removal, “ghost fences” can live on, with species continuing to behave as if a fence were still present for generations.

Knowing this, we believe that policymakers and landowners should be more cautious about installing fences in the first place. Instead of considering only a fence’s short-term purpose and the landscape nearby, we would like to see people view a new fence as yet another permanent link in a chain encircling the planet many times over.

Alex McInturff, Postdoctoral Researcher, University of California Santa Barbara; Christine Wilkinson, Ph.D. Candidate in Environmental Science, Policy and Management, University of California, Berkeley, and Wenjing Xu, PhD Candidate in Environmental Science, Policy and Management, University of California, Berkeley

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Pacific killer whales are dying — new research shows why

A female killer whale leaps from the water in Puget Sound near Seattle.
(AP Photo/Elaine Thompson)

Stephen Raverty, University of British Columbia and Joseph K. Gaydos, University of California, Davis

Killer whales are icons of the northeastern Pacific Ocean. They are intimately associated with the region’s natural history and First Nations communities. They are apex predators, with females living as long as 100 years old, and recognized a sentinels of ecosystem health — and some populations are currently threatened with extinction.

There are three major types of killer whales in the region: the “resident” populations that feed mainly on salmon, the “transients” that prey on other marine mammals like seals and sea lions, and the “offshores” that transit along the continental shelf, eating fish and sharks.

In the 1990s, an abrupt decline in the fish-eating southern resident population dropped to 75 whales from 98, prompting both Canada and the United States to list them as endangered.

Emaciated female killer whale from Hawaii.
(NOAA/NMFS/PIRO), CC BY

Since then, southern resident killer whales, whose range extends from the waters off the southeast Alaska and the coast of British Columbia to California, have not recovered — only 74 remain today. Because killer whale strandings are rare, scientists have been uncertain about the causes of killer whale mortality and how additional deaths might be prevented in the future.

As a pathologist and wildlife veterinarian, and with the help of countless biologists and veterinarians, we have carried out in-depth investigations into why killer whales in this region strand and died. If we don’t know what is causing killer whale deaths, we are not able to prevent the ones that are human-caused.

We can do better

Human activities have been implicated in the decline and lack of recovery of the southern resident killer whale population, including ship noise and strikes, contaminants, reduced prey abundance and past capture of these animals for aquariums.

Only three per cent and 20 per cent of the northern and southern resident killer whales, respectively, that died between 1925 and 2011 were even found and available for a post-mortem exam. And in most cases, only cursory or incomplete post-mortem exams can be done, generating a limited amount of information.

To figure out why these killer whales are dying — and what it means for the health of individual animals and the population as a whole — we reviewed the post-mortem records of 53 animals that became stranded in the eastern Pacific Ocean and Hawaii between 2004 and 2013. We identified the cause of death in 22 animals, and gained important insight from nine other animals where the cause of death could not be determined.

Human-caused injuries were found in nearly every age group of whales, including adults, sub-adults and calves. Some had ingested fishing hooks, but evidence of blunt-force trauma, consistent with ship and propeller strikes, was more common.

The 18-year-old male southern resident killer whale, J34, stranded near Sechelt, B.C., on Dec. 21, 2016. Post-mortem examination suggested he died from trauma consistent with vessel strike.
(Paul Cottrell/Fisheries and Oceans Canada), Author provided

This is the first study to document the lesions and forensic evidence of lethal trauma from ship and propeller strikes.

In recent years governments have focused on limiting vessel noise and disturbance. This study reinforces the need for this, showing that in addition to noise and disturbance, vessel strikes are an important cause of death in killer whales.

Direct human impact

We also developed a body condition index to evaluate the animals’ nutritional health — were they eating enough salmon, for example — to see what role food might play in the sickness and death of stranded animals. Observations of free-ranging killer whales from boats and by unmanned aerial drones have documented sub-optimal body condition or generalized emaciation in many southern resident killer whales.

In this study, we found that longer and therefore older animals tend to have thicker blubber. Our study also found that those animals that died from blunt-force trauma had a better body condition — they were in good health before death. Those that died from infections or nutritional causes were more likely to be in worse body condition.

This new body condition index can help scientists better understand the health of killer whales, and gives us a tool to evaluate their health regardless of their age, reproductive status and health condition.

Our team, working with numerous collaborators including the National Marine Mammal Foundation, is building a health database of the killer whales living in the northeastern Pacific Ocean so that their health can be tracked over time. This centralized database will let stranding response programs, regional and national government agencies and First Nations communities collaborate with field biologists, research scientists and veterinarians.

Ultimately, the information about the health of these killer whales must be conveyed to the public and policy-makers to ensure that the appropriate legislation is enacted to reverse the downward trend in the health and survival of these killer whales. We should now be able to assess future efforts and gain a better understanding of the impact of ongoing human activities, such as fishing, boating and shipping.

Stephen Raverty, Adjunct professor, Veterinary Pathology, University of British Columbia and Joseph K. Gaydos, Wildlife Veterinarian and Science Director, The SeaDoc Society, University of California, Davis

This article is republished from The Conversation under a Creative Commons license. Read the original article.