How much plastic does it take to kill a turtle? Typically just 14 pieces



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Plastic bags, balloons, and rope fragments were among more than 100 pieces of plastic in the gut of a single turtle.
Qamar Schuyler, Author provided

Britta Denise Hardesty, CSIRO; Chris Wilcox, CSIRO; Kathy Ann Townsend, University of the Sunshine Coast, and Qamar Schuyler, CSIRO

We know there is a lot of plastic in the ocean, and that turtles (and other endangered species) are eating it. It is not uncommon to find stranded dead turtles with guts full of plastic.

But we weren’t really sure whether plastic eaten by turtles actually kills them, or if they just happen to have plastic inside them when they die. Another way to look at it would be to ask: how much is too much plastic for turtles?

This is a really important question. Just because there’s a lot of plastic in the ocean, we can’t necessarily presume that animals are dying from eating it. Even if a few animals do, that doesn’t mean that every animal that eats plastic is going to die. If we can estimate how much plastic it takes to kill a turtle, we can start to answer the question of exactly how turtle populations are affected by eating plastic debris.




Read more:
Eight million tonnes of plastic are going into the ocean each year


In our research, published today in Nature Scientific Reports, we looked at nearly 1,000 turtles that had died and washed up on beaches around Australia or were found in nets. About 260 of them we examined ourselves; the others were reported to the Queensland Turtle Stranding Database. We carefully investigated why the turtles died, and for the ones we examined, we counted how many pieces of plastic they had eaten.

Some turtles died of causes that were nothing to do with plastic. They may have been killed by a boat strike, or become entangled in fishing lines or derelict nets. Turtles have even been known to die after accidentally eating a blue-ringed octopus. Others definitely died from eating plastic, with the plastic either puncturing or blocking their gut.

One of the first meals eaten by this sea turtle post-hatchling turned out to be deadly. It died from consuming more than 20 tiny pieces of plastic, many of which were about the same size as a grain of rice.
Kathy Townsend, Author provided

Some turtles that were killed by things like boat strikes or fishing nets nevertheless had large amounts of plastic in their guts, despite not having been killed by eating plastic. These turtles allow us to see how much plastic an animal can eat and still be alive and functioning.

The chart below sets out this idea. If an animal drowned in a fishing net, its chance of being killed by plastic is zero – and it falls in the lower left of the graph. If a turtle’s gut was blocked by a plastic bag, its chance of being killed by plastic is 100%, and it’s in the upper right.

The animals that were dead with plastic in their gut, but had other possible causes of death have a chance of death due to plastic somewhere between 0 and 100% – we just don’t know, and they can fall anywhere in the graph. Once we have all the animals in the plot, then we can ask whether we see an increase in the chance of death due to plastic as the amount of plastic in an animal goes up.

Conceptual framework for estimating the probability of death due to plastic debris ingestion. Figure provided by the authors.

We tested this idea using our turtle samples. We looked at the relationship between the likelihood of death due to plastic as determined by a turtle autopsy, and the number of pieces of plastic found inside the animals.

Unsurprisingly, we found that the more plastic pieces a turtle had inside it, the more likely it was to have been killed by plastic. We calculated that for an average-sized turtle (about 45cm long), eating 14 plastic items equates to a 50% chance of being fatal.




Read more:
Pristine paradise to rubbish dump: the same Pacific island, 23 years apart


That’s not to say that a turtle can eat 13 pieces of plastic without harm. Even a single piece can potentially kill a turtle. Two of the turtles we studied had eaten just one piece of plastic, which was enough to kill them. In one case, the gut was punctured, and in the other, the soft plastic had clogged the turtle’s gut. Our analyses suggest that a turtle has a 22% chance of dying if it eats just one piece of plastic.

A green sea turtle that died after consuming 13 pieces of soft plastic and balloons, which blocked its gastrointestinal system.
Kathy Townsend

A few other factors also affected the animals’ chance of being killed by plastic. Juveniles eat more debris than adults, and the rate also varies between different turtle species.

Now that we know how much is too much plastic, the next step is to apply this to global estimates of debris ingestion rates by turtles, and figure out just how much of a threat plastic is to endangered sea turtle populations.The Conversation

Britta Denise Hardesty, Principal Research Scientist, Oceans and Atmosphere Flagship, CSIRO; Chris Wilcox, Senior Research Scientist, CSIRO; Kathy Ann Townsend, Lecturer in Animal Ecology, University of the Sunshine Coast, and Qamar Schuyler, Research Scientist, Oceans and Atmospheres, CSIRO

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

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A hidden toll: Australia’s cats kill almost 650 million reptiles a year



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A feral cat snapped by a remote camera in the wild.
NT government, Author provided

John Woinarski, Charles Darwin University; Brett Murphy, Charles Darwin University; Chris Dickman, University of Sydney; Sarah Legge, Australian National University, and Tim Doherty, Deakin University

Cats take a hefty toll on Australia’s reptiles – killing an estimated 649 million of them every year, including threatened species – according to our new research published in the journal Wildlife Research.

This follows the earlier discovery that cats take a similarly huge chunk out of Australian bird populations. As we reported last year, more than a million Australian birds are killed by cats every day. Since their introduction to Australia, cats have also driven many native mammal species extinct.




Read more:
For whom the bell tolls: cats kill more than a million Australian birds every day


We collated information from about 100 previous local studies of cats’ diets across Australia. These studies involved teasing apart the contents of more than 10,000 samples of faeces or stomachs from cats collected as part of management programs.

We tallied the number of reptiles found in these samples, and then scaled it up to Australia’s estimated cat population of between 2.1 million and 6.3 million. We also collated information from museums and wildlife shelters on the various animals that had been brought in after being killed or injured by cats.

We calculate that an average feral cat kills 225 reptiles per year, so the total feral cat population kills 596 million reptiles per year. This tally will vary significantly from year to year, because the cat population in inland Australia fluctuates widely between drought and rainy years.

On the hunt.
NT government, Author provided

We also estimated that the average pet cat kills 14 reptiles per year. That means that Australia’s 3.9 million pet cats kill 53 million reptiles in total each year. However, there is much less firm evidence to quantify the impact of pet cats, mainly because it is much more straightforward to catch and autopsy feral cats to see what they have been eating, compared with pet cats.

Binge eaters

According to our study, cats have been known to kill 258 different Australian reptiles (snakes, lizards and turtles – but not crocodiles!), including 11 threatened species.

The cat autopsies revealed that some cats binge on reptiles, with many cases of individual cats having killed and consumed more than 20 individual lizards within the previous 24 hours. One cat’s stomach was found to contain no less than 40 lizards.

Cat stomach contents, including several reptile parts.
Arid Recovery, Author provided

Such intensive predation probably puts severe pressure on local populations of some reptile species. There is now substantial evidence that cats are a primary cause of the ongoing decline of some threatened Australian reptile species, such as the Great Desert Skink.

By our estimate, the average Australian feral cat kills four times more lizards than the average free-roaming cat in the United States (which kills 59 individuals per year). But there are many more such cats in the US (between 30 million and 80 million), so the total toll on reptiles is likely similar.




Read more:
The war on feral cats will need many different weapons


The conservation of the Australian reptile fauna has been accorded lower public profile than that of many other groups. However, a recent international program has nearly completed an assessment of the conservation status of every one of Australia’s roughly 1,000 lizard and snake species.

Our research provides yet more evidence of the harm that cats are wreaking on Australia’s native wildlife. It underlines the need for more effective and strategic control of Australia’s feral cats, and for more responsible ownership of pet cats.

Pet cats that are allowed to roam will kill reptiles, birds and other small animals. Preventing pet cats from roaming will help the cats live longer and healthier lives – not to mention saving the lives of wildlife.


The ConversationThe authors acknowledge the contribution of Russell Palmer, Glenn Edwards, Alex Nankivell, John Read and Dani Stokeld to this research.

John Woinarski, Professor (conservation biology), Charles Darwin University; Brett Murphy, Senior Research Fellow, Charles Darwin University; Chris Dickman, Professor in Terrestrial Ecology, University of Sydney; Sarah Legge, Associate Professor, Australian National University, and Tim Doherty, Research Fellow, Deakin University

This article was originally published on The Conversation. Read the original article.

For whom the bell tolls: cats kill more than a million Australian birds every day



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On the prowl in the outback.
Hugh McGregor/Arid Recovery, Author provided

John Woinarski, Charles Darwin University; Brett Murphy, Charles Darwin University; Leigh-Ann Woolley, Charles Darwin University; Sarah Legge, Australian National University; Stephen Garnett, Charles Darwin University, and Tim Doherty, Deakin University

Cats kill more than a million birds every day across Australia, according to our new estimate – the first robust attempt to quantify the problem on a nationwide scale.

By combining data on the cat population, hunting rates and spatial distribution, we calculate that they kill 377 million birds a year. Rates are highest in Australia’s dry interior, suggesting that feral cats pose a serious and largely unseen threat to native bird species.


Read more: Ferals, strays, pets: how to control the cats that are eating our wildlife


This has been a contentious issue for more than 100 years, since the spread of feral cats encompassed the entire Australian mainland. In 1906 the ornithologist A.J. Campbell noted that the arrival of feral cats in a location often immediately preceded the decline of many native bird species, and he campaigned vigorously for action:

Undoubtedly, if many of our highly interesting and beautiful birds, especially ground-loving species, are to be preserved from total extinction, we must as a bird-lovers’ union, at no distant date face squarely a wildcat destruction scheme.

His call produced little response, and there has been no successful and enduring reduction in cat numbers since. Nor, until now, has there been a concerted effort to find out exactly how many birds are being killed by cats.

Counting the cost

To provide a first national assessment of the toll taken by cats on Australian birds, we have compiled almost 100 studies detailing the diets of Australia’s feral cats. The results show that the average feral cat eats about two birds every five days.

We then combined these statistics with information about the population density of feral cats, to create a map of the estimated rates of birds killed by cats throughout Australia.

Number of birds eaten per square kilometre.
Brett Murphy, Author provided

We conclude that, on average, feral cats in Australia’s largely natural landscapes kill 272 million birds per year. Bird-kill rates are highest in arid Australia (up to 330 birds per square km per year) and on islands, where rates can vary greatly depending on size.

We also estimate (albeit with fewer data) that feral cats in human-modified landscapes, such as the areas surrounding cities, kill a further 44 million birds each year. Pet cats, meanwhile, kill about 61 million birds per year.

Overall, this amounts to more than 377 million birds killed by cats per year in Australia – more than a million every day.

Which species are suffering?

In a related study, we also compiled records of the bird species being killed by cats in Australia. We found records of cats killing more than 330 native bird species – about half of all Australia’s resident bird species. In natural and remote landscapes, 99% of the cat-killed birds are native species. Our results also show that cats are known to kill 71 of Australia’s 117 threatened bird species.

Birds that feed or nest on the ground, live on islands, and are medium-sized (60-300g) are most likely to be killed by cats.

Galahs are among the many native species being killed by feral cats.
Mark Marathon, Author provided

It is difficult to put a million-plus daily bird deaths in context without a reliable estimate of the total number of birds in Australia. But our coarse assessment from many published estimates of local bird density suggests that there are about 11 billion land birds in Australia,
suggesting that cats kill about 3-4% of Australia’s birds each year.

However, particular species are hit much harder than others, and the population viability of some species (such as quail-thrushes, button-quails and ground-feeding pigeons and doves) is likely to be especially threatened.

Our tally of bird deaths is comparable to similar estimates for other countries. Our figure is lower than a recent estimate for the United States, and slightly higher than in Canada. Overall, bird killings by cats seem to greatly outnumber those caused by humans.

In Australia, cats are likely to significantly increase the extinction risk faced by some bird species. In many locations, birds face a range of interacting threats, with cat abundance and hunting success shown to increase in fragmented bushland, in areas with high stocking rates, and in places with poorly managed fire regimes, so cat impacts compound these other threats.

Belling the cat

What can be done to reduce the impact? The federal government’s Threatened Species Strategy recognises the threat posed by feral cats, albeit mainly on the basis of their role in mammal extinctions.

The threatened species strategy also prioritised efforts to control feral cats more intensively, eradicate them from islands with important biodiversity values, and to expand a national network of fenced areas that excludes feral cats and foxes.

But while fences can create important havens for many threatened mammals, they are much less effective for protecting birds. To save birds, cats will need to be controlled on a much broader scale.


Read more: The war on feral cats will need many different weapons


We should also remember that this is not just a remote bush problem. Roughly half of Australia’s cats are pets, and they also take a considerable toll on wildlife.

While recognising the many benefits of pet ownership, we should also work to reduce the detrimental impacts. Fortunately, there is increasing public awareness of the benefits of not letting pet cats roam freely. With such measures, cat owners can help to look after the birds in their own backyards, and hence contribute to conserving Australia’s unique wildlife.


The ConversationWe acknowledge the contribution of Russell Palmer (WA Department of Biodiversity Conservation and Attractions), Chris Dickman (University of Sydney), David Paton (University of Adelaide), Alex Nankivell (Nature Foundation SA Inc.), Mike Lawes (University of KwaZulu-Natal), and Glenn Edwards (Department of Environment and Natural Resources) to this article.

John Woinarski, Professor (conservation biology), Charles Darwin University; Brett Murphy, Senior Research Fellow, Charles Darwin University; Leigh-Ann Woolley, Research Associate, Charles Darwin University; Sarah Legge, Associate Professor, Australian National University; Stephen Garnett, Professor of Conservation and Sustainable Livelihoods, Charles Darwin University, and Tim Doherty, Research Fellow, Deakin University

This article was originally published on The Conversation. Read the original article.

Little shop of horrors: the Australian plants that can kill you


Ben Moore, Western Sydney University

Australia is so famous for its dangerous creatures that visitors often arrive fearful that everything that moves is out to get them. In a land where snakes, spiders, shells and even one of the iconic mammals – the platypus – can bite or sting, should we all be worried about plants as well?

Plants around the world produce a staggering diversity of chemicals and many of these are potentially toxic to animals including humans, sometimes even upon contact. Many of these toxins have evolved to protect plant roots, leaves and unripe fruits from being eaten by herbivores, particularly insects and browsing mammals.

Australia’s toxic plants are not terribly appealing or nutritious for humans. If someone is poisoned, it’s usually accidental, and many victims are curious children.

There are many historical records of plant poisoning in Australia involving early explorers and settlers who were short of supplies or looking for new sources of food. Today, though, plant poisoning accounts for less than 1% of calls to poisons information lines in Australia.

Animals beware

The threat of poisoning to livestock is much more substantial and causes significant economic and animal welfare impacts.

It’s in the interests of cattle and sheep to become expert botanists, but even experts can get things wrong when confronted with something they’ve never seen before. Most livestock poisonings occur when animals are moving through new country or are put into new paddocks with unfamiliar plants.

Native plants that kill significant numbers of livestock include Cooktown ironwood in northern Australia (as little as 50 grams of leaf can contain a quantity of alkaloids that can kill a bull) and the poison peas and heart-leafed poison bush of Western Australia and Queensland respectively (Gastrolobium), which contain a deadly metabolic poison, sodium fluoroacetate.

Elsewhere, introduced pasture weeds such as fireweed, Senecio madagasciarensis, and Paterson’s curse, Echium plantagenium, pose significant threats to cattle, sheep and horses.

It’s in the dose

The adage that “the poison is in the dose” is correct in that small amounts of most poisonous plants are unlikely to cause permanent damage or death, although there are exceptions. Indeed, most herbivores have to tolerate some exposure to plant poisons because they’re so widespread among the plants they eat.


CC BY-NC-ND

Small amounts of some toxic compounds can even be beneficial and sometimes have traditional or medical uses. Aboriginal people, for instance, used Duboisia hopwoodii and other native tobacco species (Nicotiana) to produce a powerful and widely traded stimulant, pituri, the active ingredient of which is the potent alkaloid, nicotine.

Similarly, atropine, an alkaloid found in Angels’ trumpets and thorn-apple (Brugmansia and Datura species) is a powerful hallucinogen and toxin. But it’s also a valuable drug used to treat some heart and nervous conditions, as well as poisoning by some other plant alkaloids and cardiac glycosides.

Knowing what dose of poison a plant contains is not always easy. How much toxin an individual plant contains can vary with season, the age of the plant, soil type, drought and the plant’s genes. Just as you may be tall and your next-door neighbour short, two plants of the same species growing alongside can vary in how much toxin they produce.

On top of that, different animal species and individual people and animals can also vary in their ability to tolerate poisons. This makes ingesting toxic plants a little like Russian roulette: there’s a strong element of chance.

Deadly relatives

A significant number of Australia’s more than 20,000 plants are potentially toxic. In many cases, Australia has species or subspecies of plants that are closely related to well-known toxic plants from elsewhere. But their relative toxicity is not well established.

The Indian suicide tree, Cerbera odollum, has been described as the “perfect murder weapon”, for instance, but the toxicity of our native Cerbera manghas is less well understood, despite the fact it possesses the same cardiac poisons.

Similarly, how our native strychnine bushes Strychnos lucida and S. psilosperma compare to the better-known strychnine tree S. nux-vomica from India is not well known, but they do also produce strychnine.

Unless you’re a hungry ruminant, you’re probably unlikely to suffer death by plant poisoning in Australia, but the risk is nonetheless real. It pays to realise that garden plants and even common indoor plants are sometimes just as dangerous as what lurks in the bush. Parents and outdoorsy types should be aware of the risks posed by contact with or ingestion of plants.

This article is part of our series Deadly Australia. Stay tuned for more pieces on the topic in the coming days.

The Conversation

Ben Moore, Senior Lecturer in Ecology, Hawkesbury Institute for the Environment, Western Sydney University

This article was originally published on The Conversation. Read the original article.

South Africa: Rhino Poaching Continuing to Kill Many Rhinos


The article below reports on the large number of Rhinos lost to poaching this year in South Africa.

For more, visit:
http://www.cbsnews.com/8301-501710_162-57399946/135-endangered-rhino-killed-in-south-africa/