Fences Can 'Utterly Reorganize' Ecosystems, Producing Winners and Losers, but Are Rarely Studied
By Alex McInturff, Christine Wilkinson and Wenjing Xu
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.
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
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.
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.
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.
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
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.
Some incredible non-COVID19 content for you today: hundreds of pronghorn (aka speed goats!) migrating through Natro… https://t.co/OieLvGhbqU— Ben Goldfarb (@Ben Goldfarb)1584554289.0
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.
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 is a postdoctoral researcher at the University of California, Santa Barbara.
Christine Wilkinson is a Ph.D. candidate in environmental science, policy and management at the University of California, Berkeley.
Wenjing Xu is a Ph.D. candidate in environmental science, policy and management at the University of California, Berkeley.
Disclosure statements: Wenjing Xu receives funding from the Smithsonian Institute. Alex McInturff and Christine Wilkinson do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.
Reposted with permission from The Conversation.
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In celebration of Earth Day, a star-studded cast is giving fans a rare glimpse into the secret lives of some of the planet's most majestic animals: whales. In "Secrets of the Whales," a four-part documentary series by renowned National Geographic Photographer and Explorer Brian Skerry and Executive Producer James Cameron, viewers plunge deep into the lives and worlds of five different whale species.
<span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="b102b19b2719f50272ab718c44703dd0"><iframe lazy-loadable="true" src="https://www.youtube.com/embed/xOySOlB78dM?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span>
Herring are a primary food source for Norway's orcas. Luis Lamar / National Geographic for Disney+
Belugas are extremely social creatures with a varied vocal range. Peter Kragh / National Geographic for Disney+
A Southern Right whales is pictured in the accompanying book, "Secrets of the Whales." Brian Skerry / National Geographic
The coronavirus has isolated many of us in our homes this year. We've been forced to slow down a little, maybe looking out our windows, becoming more in tune with the rhythms of our yards. Perhaps we've begun to notice more, like the birds hopping around in the bushes out back, wondering (maybe for the first time) what they are.
A Coeligena helianthea hummingbird is photographed during a birdwatching trail at the Monserrate hill in Bogota on November 11, 2020. Colombia is the country with the largest bird diversity in the world, home to about 1,934 different bird species, a fifth of the total known. JUAN BARRETO / AFP / Getty Images
1. Choosing the Right Binoculars<p>Binoculars are a relatively indispensable tool for most birders – but, for those just starting out, it might not yet be worth the several-hundred-dollar investment. If you aren't able to scour the attics of friends or borrow a pair from a fellow bird watcher, some local birding and naturalist groups have <a href="https://vashonaudubon.org/all-about-vashon-birds/binoculars-check-out/" target="_blank">binocular loaning programs</a> for members, allowing you to plan ahead for a day (or week) of birding.</p><p>When you're ready to take the plunge, choosing a pair or binoculars should take some careful deliberation based on your needs and preferences; some <a href="https://www.birdwatchersdigest.com/bwdsite/explore/optics/top-10-tips-buying-binoculars-bird-watching.php" target="_blank">major considerations</a> might include size, ease of use, <a href="https://www.rei.com/learn/expert-advice/binoculars.html" target="_blank" rel="noopener noreferrer">magnification</a>, and price. While professional binoculars can easily run north of $1,000, there are plenty of perfectly suitable entry-level binoculars under $200. You might not get the perfect precision and clarity of more elite models, but a less expensive pair will allow you to strengthen your birding skills while deciding if you're interested in investing in a premium pair.</p><p>For a budget-friendly option, check out resale options on eBay, Facebook marketplace, or neighborhood yard sales: you might find a nicer pair whose retail price isn't within your budget.</p>
2. Know What Birds Are in Your Area<p>When I began to pay more attention to the birds just outside my apartment building, I started to learn what species have always been around me: European starlings, house sparrows, blue jays, black capped chickadees, and the occasional red-bellied woodpecker. They had always been there, but I hadn't ever taken the time to identify them. Once you learn to <a href="https://www.audubon.org/news/get-know-these-20-common-birds_" target="_blank" rel="noopener noreferrer">recognize common birds</a> in your area, you'll be able to identify the typical species right outside your window and in your community. Of course, permanent residential birds in your neighborhood will <a href="https://nestwatch.org/learn/focal-species/" target="_blank" rel="noopener noreferrer">vary by region</a>, as will those migrating through it.</p>
3. Get Out and Explore<p>Venturing elsewhere might allow you to spot some different species beyond those frequenting your backyard. Anywhere with water or greenery offers a place for birding; as an urbanite myself, I've found that even small- and mid-sized parks in New York City allow me to find more elusive birds (although Central Park takes the crown for an afternoon of urban birding).</p><p>If you are able to travel a bit further from home, <a href="https://www.fws.gov/refuges/" target="_blank">national wildlife refuges</a> and <a href="https://www.americasstateparks.org/" target="_blank" rel="noopener noreferrer">state/national parks</a> are excellent places to explore bird habitats and perhaps log some less-common sightings. The American Birding Association also lists <a href="https://www.aba.org/aba-area-birding-trails/" target="_blank" rel="noopener noreferrer">birding trails by state</a>, and Audubon and BirdLife International identify <a href="https://www.audubon.org/important-bird-areas" target="_blank" rel="noopener noreferrer">Important Bird Areas (IBAs)</a> across the country – important bird habitats and iconic places that activists are fighting to protect – where birders can spot birds of significance.</p>
4. Finding a Bird: Stop, Look, Listen, Repeat<p>The National Audubon Society recommends the "<a href="https://www.audubon.org/news/how-find-bird" target="_blank">stop, look, listen, repeat</a>" mantra when seeking and identifying birds.</p><p>First and foremost, spotting birds requires attention. Stopping – getting out of the car, pausing on the sidewalk, trail, or in the backyard to look up – is the most important step.</p><p>When looking for birds, try to avoid gazing wildly around; rather, scan your surroundings, focusing on any odd shapes or shadows, trying to think about where a bird might perch (power lines, fence posts, branches), or keep an eye on the sky for flying eagles and hawks. In open areas like fields and beaches, you might have a more panoramic view, and can take in different sections of the landscape at a time. Look around with the naked eye before reaching for the binoculars to hone in.</p><p>While it can be hard to sift through the noise, listening for birds is perhaps an even more important element of bird watching than looking. Once you spend more time in the field, you'll be able to parse apart the racket and identify specific species, especially aided by Audubon's Bird Guide app or by learning from their <a href="https://www.audubon.org/section/birding-ear" target="_blank">Birding by Ear series</a>.</p><p>Repeat this pattern as you continue on your way, stopping to look and listen for birds as you go, rather than waiting for them to come to you. </p>
5. Identification<p>When you head out for a day of bird watching – especially when you're hoping to spot some new species – you'll want to be armed with the tools to identify what you see. <a href="https://www.audubon.org/news/how-identify-birds" target="_blank" rel="noopener noreferrer">Major considerations when identifying birds</a> are their group (such as owls, hawks, or sparrow-like birds), size and shape, behavior, voice, field marks, season, and habitat.</p><p>The <a href="https://www.sibleyguides.com/about/the-sibley-guide-to-birds/" target="_blank" rel="noopener noreferrer">Sibley Guide to Birds</a> and the <a href="https://www.hmhbooks.com/shop/books/peterson-field-guide-to-birds-of-north-america-second-edition/9781328771445" target="_blank" rel="noopener noreferrer">Peterson Field Guide</a> are widely considered the best books for identifying birds in North America, although many <a href="https://www.audubon.org/news/what-bird-guide-best-you" target="_blank" rel="noopener noreferrer">specialized guides</a> focus on specific species or regions as well.</p><p>Plenty of <a href="https://blog.nature.org/science/2013/05/27/boucher-bird-blog-apps-smart-birder/" target="_blank" rel="noopener noreferrer">bird identification apps</a> have popped up in recent years – including National Geographic Birds, Sibley eGuide to Birds, iNaturalist, Merlin Bird ID, and Birdsnap – which are basically a <a href="https://www.audubon.org/news/the-best-birding-apps-and-field-guides" target="_blank" rel="noopener noreferrer">field guide in your pocket</a>. I'm partial to the Audubon Bird Guide, which allows users to filter by common identifiers, including a bird's habitat, color, activity, tail shape, and general type, adding them all to a personal map to view your sightings.</p>
6. Recording Your Sightings<p><span>As you deepen your commitment to birding, you might join the community of birders that track and quantify their sightings, building their </span><a href="https://www.thespruce.com/what-birds-count-on-a-life-list-386704#:~:text=A%20life%20list%20is%20a,which%20birds%20you%20have%20seen." target="_blank" rel="noopener noreferrer">life list</a><span>.</span></p><p>While a standard notebook noting the date, species name, habitat, vocalizations, or any other data you wish to include will suffice, some birders opt for a more <a href="https://www.riteintherain.com/no-195-birders-journal" target="_blank" rel="noopener noreferrer">structured birder's journal</a> with pre-determined fields to record your encounters, take notes, draw sketches, etc.</p><p>Many birders also choose to record their sightings online and in shared databases (which include many of the field guide apps), often pinpointing them on a map for others to view. Launched by the Cornell Lab of Ornithology and Audubon, <a href="https://ebird.org/home" target="_blank" rel="noopener noreferrer">eBird is one of the largest databases and citizen science projects around birding</a>, where hundreds of thousands of birders enter their sightings, and users can explore birds in regions and hotspots around the world. Users can also record their sightings on the <a href="https://apps.apple.com/us/app/ebird/id988799279" target="_blank" rel="noopener noreferrer">eBird app</a>.</p>
7. Attracting Birds to Your Own Yard<p>Feeding birds is a common phenomenon: more than 40% of Americans maintain a birdfeeder to attract birds and watch them feast.</p><p>Not all birdfeed is created equal, however. Many commercial varieties are mostly made with "fillers" (oats, red millet, etc.) that birds will largely leave untouched. After researching what birds to expect in your area – and which ones you want to attract – you can create your own birdfeed with <a href="https://www.allaboutbirds.org/news/types-of-bird-seed-a-quick-guide/?pid=1142" target="_blank">seeds that will appeal to them</a>.</p><p>Beyond filling a birdfeeder, <a href="https://www.ecowatch.com/eco-friendly-lawn-2651194858.html" target="_self">transforming your yard into an eco-friendly oasis</a> is by far the best way to attract birds. Choosing to forgo mowing your lawn, planting native flowers and grasses, and ditching the pesticides will bring back the bugs that birds feed on, and provide a safe haven in which birds can happily live and eat.</p><p>While it's widely considered acceptable – and even beneficial – to feed birds with appropriate seeds, communal birdfeeders often <a href="https://www.audubon.org/news/to-feed-or-not-feed" target="_blank" rel="noopener noreferrer">foster unlikely interactions between different species</a>, who can then transmit harmful diseases and parasites to one another. Maintaining several bird feeders with different types of seeds might keep different species from coming into contact, and feeders can be <a href="https://www.allaboutbirds.org/news/how-to-clean-your-bird-feeder/" target="_blank" rel="noopener noreferrer">cleaned to prevent the spread of infection</a>.</p>
8. Inclusivity and Anti-Racism in the Birding Community<p>Like all outdoor activities and areas of scientific study, birding communities are subject to racist and discriminatory ideologies. Black birders have long experienced discrimination and underrepresentation in outdoor spaces. The work of organizations like the <a href="https://www.instagram.com/birdersfund/" target="_blank">Black & Latinx Birders Fund</a>, <a href="https://www.instagram.com/birdability/" target="_blank">Birdability</a>, and <a href="https://www.instagram.com/feministbirdclub/" target="_blank">Feminist Bird Club</a> highlight the contributions and importance of birders of color, birders with disabilities, and women and LGBTQ+ birders to the birding community, as do activists and naturalists like <a href="https://www.instagram.com/hood__naturalist/" target="_blank">Corina Newsome</a> and <a href="https://www.instagram.com/tykeejames/" target="_blank">Tykee James</a>. The work of <a href="https://www.audubon.org/news/its-bird-new-comic-written-central-park-birder-christian-cooper" target="_blank">Christian Cooper</a>, <a href="https://camilledungy.com/publications/" target="_blank">Camille Dungy</a> (read her poem <a href="https://www.poetryfoundation.org/poetrymagazine/poems/58363/frequently-asked-questions-10" target="_blank">Frequently Asked Questions: 10</a>), and <a href="https://orionmagazine.org/article/9-rules-for-the-black-birdwatcher/" target="_blank">J. Drew Lanham</a> – including his essay "<a href="https://lithub.com/birding-while-black/" target="_blank">Birding While Black</a>" – are a great place to start.</p><p>Getting involved in birding means educating ourselves on these issues and taking meaningful action; the work of <a href="https://www.audubon.org/news/its-bird-new-comic-written-central-park-birder-christian-cooper" target="_blank">Christian Cooper</a> and <a href="https://orionmagazine.org/article/9-rules-for-the-black-birdwatcher/" target="_blank">J. Drew Lanham</a> – including his essay "<a href="https://lithub.com/birding-while-black/" target="_blank" rel="noopener noreferrer">Birding While Black</a>" – are a great place to start. Just as birders are activists for protecting habitats and natural areas, we must also be active and aware of inclusivity in these spaces.</p>
9. Get Involved<p>To learn from and enjoy the company of other birders, check out local birding groups in your area to join. Many Audubon chapters host trips, meetings, and bird walks for members. The American Birding Association even maintains a <a href="https://www.aba.org/festivals-events/" target="_blank">directory of birding festivals</a> across the country.</p><p>Volunteering for birds is also a great way to meet other birders and take action for birds in your community; local organizations might have opportunities for assisting with habitat restoration or helping at birding centers.</p><p>Like all wildlife, climate change and habitat destruction threaten the livelihood of birds, eliminating their breeding grounds and food sources. A <a href="https://www.audubon.org/climate/survivalbydegrees" target="_blank">2019 report released by the National Audubon Society</a> found that two-thirds of North American birds may face extinction if global temperatures rise 5.4 degrees Fahrenheit by 2100. Staying informed about and taking action for legislation designed to protect birds and our climate – such as the recent <a href="https://www.congress.gov/bill/116th-congress/house-bill/5552/text" target="_blank" rel="noopener noreferrer">Migratory Bird Protection Act</a> – is important for ensuring a livable future for wildlife and humans alike.</p><p><em>Linnea graduated from Skidmore College in 2019 with a Bachelor's degree in English and Environmental Studies, and now lives in Brooklyn, New York. Most recently, Linnea worked at Hunger Free America, and has interned with WHYY in Philadelphia, Saratoga Living Magazine, and the Sierra Club in Washington, DC. </em><em>Linnea enjoys hiking and spending time outdoors, reading, practicing her German, and volunteering on farms and gardens and for environmental justice efforts in her community. Along with journalism, she is also an essayist and writer of creative nonfiction.</em></p>
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