Cats Wreak Havoc on Native Wildlife, but We’ve Found One Adorable Species Outsmarting Them
By Euan Ritchie, Amy Coetsee, Anthony Rendall, Tim Doherty and Vivianna Miritis
But we've found one mammal in particular that can outsmart cats and live alongside them: the long-nosed potoroo.
These miniature kangaroo-like marsupials are officially listed as vulnerable. And after the recent devastating fires, extensive swathes of their habitat in southeastern Australia were severely burnt, leaving them more exposed to predators such as foxes and cats. But the true extent of the impact on their numbers remains unclear.
Amid the devastation, our new study is reason to be optimistic.
Using motion-sensing camera traps on the wildlife haven of French Island – which is free of foxes, but not cats – we found potoroos may have developed strategies to avoid prowling cats, such as hiding in dense vegetation.
If these long-nosed potoroos can co-exist with one of the world's most deadly predators, then it's time we rethink our conservation strategies.
Long-nosed potoroos are a bit like mini kangaroos, but spend much of their time digging for fungi. Zoos Victoria
Surviving Cats With a Deadly Game of Hide and Seek
We conservatively estimated that between five and 14 cats lived in our study area (but it takes only one cat to eradicate a population of native animals).
Although cats were common here, we detected them less often in areas of dense vegetation. By contrast, this was where we found potoroos more often.
French Island's thick vegetation provides potoroos with critical refuge to evade feral cats. Vivianna Miritis
Long-nosed potoroos are nocturnal foragers that mainly, but not exclusively, feed in more open habitat before sheltering in dense vegetation during the day. But we found potoroos rarely ventured out of their thick vegetation shelter.
This may be because they're trading off potentially higher quality foraging habitat in more open areas against higher predation risk. In other words, it appears they've effectively learnt to hide from the cats.
Another intriguing result from our study was that although potoroos and feral cats shared more than half of their activity time, the times of peak activity for each species differed.
Cats were active earlier in the night, while potoroo activity peaked three to four hours later. This might be another potoroo strategy to avoid becoming a cat's evening meal.
Temporal activity of cats and long-nosed potoroos for winter and summer, on French Island, Victoria. Their overlap is represented by the area shaded in grey. Modified from Miritis et al. (2020).
Still, completely avoiding cats isn't possible. Our study site was in the national park on French Island, and it's likely cats saturate this remnant patch of long-nosed potoroo habitat.
It's also possible cats may be actively searching for potoroos as prey, and indeed some of our camera images showed cats carrying young long-nosed potoroos in their mouths. These potoroos were more likely killed by these cats, rather than scavenged.
Cats Are Expert Hunters
Cats are exceedingly difficult to manage effectively. They're adaptable, elusive and have a preference for live prey.
The two most common management practices for feral cats are lethal control and exclusion fencing. Lethal control needs to be intensive and conducted over large areas to benefit threatened species.
And outside of predator-free sanctuaries, it must be ongoing. If control stops, cats can reinvade from surrounding areas.
"Safe havens" – created through the use of exclusion fencing or predator-free islands – can overcome some of these challenges. But while exclusion fencing is highly effective, it can create other bad outcomes, including an over-abundance of herbivores, leading to excessive grazing of vegetation.
Camera traps can tell us a lot about how introduced predators and native wildlife interact. Zoos Victoria and Deakin University
In any case, removing introduced predators might not be really necessary in places native species can co-exist. If long-nosed potoroos have learnt to live with feral cats, we should instead focus on how to maintain their survival strategies.
Why Cat Eradication Isn't Always the Best Option
It's clear cats are here to stay, so we shouldn't simply fall back largely on predator eradication or predator-free havens as the only way to ensure our wildlife have a fighting chance at long-term survival.
Yes, for some species, it's vital to keep feral predators away. But for others like long-nosed potoroos, conserving and creating suitable habitat and different vegetation densities may be the best way to keep them alive.
But perhaps most important is having predator-savvy insurance populations, such as long-nosed potoroos on French Island. This is incredibly valuable for one day moving them to other areas where predators – native or feral – are present, such as nearby Phillip Island.
In the absence of predators, native wildlife can rapidly lose their ability to recognize predator danger. Programs aimed at eradicating introduced predators where they're co-existing with native species need to pay careful attention to this.
Euan Ritchie is an associate professor in wildlife ecology and conservation at the Centre for Integrative Ecology, School of Life & Environmental Sciences, Deakin University.
Amy Coetsee is a threatened species biologist at the University of Melbourne.
Anthony Rendall is an associate lecturer in conservation biology at Deakin University.
Tim Doherty is an ARC DECRA fellow at the University of Sydney.
Vivianna Miritis is a Ph.D. candidate at the University of Sydney.
Disclosure statements: Euan Ritchie receives funding from the Australian Research Council, The Australia and Pacific Science Foundation, Australian Geographic, Parks Victoria, Department of Environment, Land, Water and Planning, and the Bushfire and Natural Hazards CRC.
Euan Ritchie is a director (Media Working Group) of the Ecological Society of Australia, and a member of the Australian Mammal Society.
Amy Coetsee is employed by Zoos Victoria, a not-for-profit zoo-based conservation organization and is a member of the Australian Mammal Society.
Anthony Rendall is a member of the Australian Mammal Society.
Tim Doherty receives funding from the Hermon Slade Foundation, NSW Environment Trust, Australian Academy of Science and Australian Research Council. He is a board member for the Society for Conservation Biology Oceania and a member of the Ecological Society of Australia.
Vivianna Miritis is a member of the Ecological Society of Australia, Australian Mammal Society, and Royal Zoological Society of NSW.
Reposted with permission from The Conversation.
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By Robert J. Orth, Jonathan Lefcheck and Karen McGlathery
A century ago Virginia's coastal lagoons were a natural paradise. Fishing boats bobbed on the waves as geese flocked overhead. Beneath the surface, miles of seagrass gently swayed in the surf, making the seabed look like a vast underwater prairie.
Why Didn’t Seagrasses Recover Naturally?<p>Development, nutrient runoff and other human impacts have damaged marshes, mangroves, coral reefs and seagrasses in many bays and estuaries worldwide. Loss or shrinkage of these key habitats has reduced commercial fisheries, increased erosion, made coastlines more vulnerable to floods and storms and harmed many types of aquatic life. Rapid climate change has compounded these effects through <a href="https://theconversation.com/ocean-warming-has-fisheries-on-the-move-helping-some-but-hurting-more-116248" target="_blank">rising global temperatures</a>, more <a href="https://theconversation.com/more-frequent-and-intense-tropical-storms-mean-less-recovery-time-for-the-worlds-coastlines-123335" target="_blank">frequent and severe storms</a> and <a href="https://theconversation.com/as-climate-change-alters-the-oceans-what-will-happen-to-dungeness-crabs-61501" target="_blank">ocean acidification</a>.</p><p>In the late 1990s, local residents told two of us who are longtime students of seagrasses (Robert "JJ" Orth and Karen McGlathery) that they had spotted small patches of eelgrass in shallow waters off Virginia's eastern shore. For years the conventional view had been that seagrasses in this area had not recovered from the events of the 1930s because human activities had <a href="https://doi.org/10.1016/j.aquabot.2005.07.007" target="_blank">made the area inhospitable for them</a>.</p><p>But studies showed that water quality in these coastal bays was <a href="https://doi.org/10.1007/BF02782971" target="_blank" rel="noopener noreferrer">comparatively good</a>. This led us to explore a different explanation: Seeds from healthy seagrass populations elsewhere along the Atlantic coast simply weren't reaching these isolated bays. Seagrasses are underwater flowering plants, so seeds are among the main ways they reproduce and spread to new environments.</p>
Eelgrass beds were restored in four bays at the southern tip of Virginia's eastern shore on the Atlantic coast. David J. Wilcox/VIMS, CC BY-ND
Sowing a New Crop<p>From our <a href="https://doi.org/10.2307/1941597" target="_blank">earlier research</a>, we knew that when eelgrass seeds fall from the parent plant, they sink to the sea bottom quickly and don't move far from where they land. We also knew that these seeds don't germinate until late fall or early winter. This meant that if we collected the seeds in spring, when eelgrass flowers, we could hold them until the fall, helping them survive over the months in between.</p><p>We decided to try reseeding eelgrass in the areas where they were missing. Starting in 1999, we collected seeds by hand from underwater meadows in nearby Chesapeake Bay – plucking the long reproductive shoots, bringing them back to our laboratory and holding them in large outdoor seawater tanks until they released their seeds naturally. After about 10 years we started gathering the grasses using a custom-built underwater "lawn mower" to collect many more of the reproductive shoots than we could by hand.</p><p>In 2001 we sowed our first round by simply tossing seeds from a boat. Our first test plots covered 28 acres of mud flats in waters 2 to 3 feet deep. Returning the following year, we saw new seedlings sprouting up.</p><p>Each year since then, the <a href="https://www.vims.edu/" target="_blank">Virginia Institute of Marine Science</a> and the <a href="https://www.nature.org/en-us/about-us/where-we-work/united-states/virginia/" target="_blank" rel="noopener noreferrer">Nature Conservancy's Virginia Coast Reserve</a>, along with staff and students from the <a href="https://www.vcrlter.virginia.edu/" target="_blank" rel="noopener noreferrer">University of Virginia</a>, have led a team of scientists and citizens to collect and seed a combined 536 acres of bare bottom in several coastal bays.</p><p>These initial plots took off and rapidly expanded. By 2020 they covered 9,600 acres across four bays. Several factors helped them flourish. These bays are naturally flushed with cool, clean water from the Atlantic Ocean. And they lie off the tip of Virginia's eastern shore, where there is little coastal development.</p>
<span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="a482c2146febd6782c99960c2b55feb8"><iframe lazy-loadable="true" src="https://www.youtube.com/embed/K9NyfPLINtk?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span>
Sheltering Marine Life and Storing Carbon<p>Since eelgrass disappeared from these bays in the 1930s, human understanding of seagrass ecosystems has evolved. Today people don't pack their walls full of seagrass insulation but instead value different services they provide, such as habitat for fish and shellfish – including many <a href="https://doi.org/10.1111/conl.12645" target="_blank" rel="noopener noreferrer">commercially and recreationally important species</a>.</p><p>Scientists and government agencies also have recognized the importance of coastal systems in capturing and storing so-called "<a href="https://oceanservice.noaa.gov/facts/bluecarbon.html" target="_blank" rel="noopener noreferrer">blue carbon</a>." In fact, we now know that seagrasses constitute a globally significant <a href="https://doi.org/10.1038/ngeo1477" target="_blank" rel="noopener noreferrer">carbon sink</a>. They are a key tool for reducing carbon dioxide in the atmosphere and <a href="https://doi.org/10.1038/s41598-020-64094-1" target="_blank" rel="noopener noreferrer">slowing climate change</a></p><p>We are working to understand the valuable services that our restored seagrass beds provide. To our surprise, fish and invertebrates returned within only a few years as the meadows expanded. These organisms have established extensive food webs that include species ranging from tiny seahorses to 6-foot-long sandbar sharks.<br></p><p>Other benefits were equally dramatic. Water in the bays become clearer as the seagrass canopy trapped floating particles and deposited them onto the bottom, burying significant stocks of carbon and nitrogen in sediments bound by the grasses' roots. Our research is the first to verify the overall net carbon captured by seagrass, and is now being used to issue carbon offset credits that in turn <a href="https://vaseagrant.org/eelgrass-carbon-credits/" target="_blank">create more funds for restoration</a>.</p><p>One big question was whether restoring seagrasses could make it possible to bring back bay scallops, which once generated millions of dollars for the local economy. Since bay scallops no longer existed in Virginia, we obtained broodstock from North Carolina, which we have <a href="https://chesapeakebaymagazine.com/return-of-the-bay-scallop/" target="_blank">reared and released annually</a> since 2013. Regular surveys now reveal a growing population of bay scallops in the restored eelgrass, although there is still some way to go before they reach levels seen in the 1930s.</p>
Restored seagrass beds (dark areas) along Virginia's Atlantic coast, with sunlight reflecting from a small island. Jonathan Lefcheck, CC BY-ND
A Model for Coastal Restoration<p>Repairing damaged ecosystems is such an urgent mission worldwide that the United Nations has designated 2021-2030 as the <a href="https://www.decadeonrestoration.org/" target="_blank">U.N. Decade on Ecosystem Restoration</a>. We see the success we have achieved with eelgrass restoration as a prime model for similar efforts in coastal areas around the world.</p><p>Our project focused not only on reviving this essential habitat, but also on charting how restoring seagrasses affected the ecosystem and on the co-restoration of bay scallops. It provides a road map for involving scholars, nonprofits organizations, citizens and government agencies in an ecological mission where they can see the results of their work.</p><p>Recent assessments show that the restored zone only covers about 30% of the total habitable bottom in our project area. With continued support, eelgrass – and the many benefits it provides – may continue to thrive and expand well into the 21st century.</p>
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