Archive for the ‘introduced species’ Category

feral horses

I make no bones about my view that the horses that roam the American West are feral and should not be regarded as native wildlife. This view shouldn’t controversial, but it is.

Lots of romanticism exist about horses and the West, including that brief time when Native cultures used horses as their greatest asset in hunting bison.

But the truth is that the horses one might see roaming the ranges of the American West are all derived from domestic horses that went wild on the range. The initial ones were all derived from Iberian/North African horses that Spanish colonizers brought into the New World, but these were later augmented with horses brought over from the rest of Europe.

If one were to say that the various forms of freely breeding swine in North America were feral, it would be easy to get agreement. Suids are not native to the Americas, though a sister lineage, the Tayassuidae, are native to North America. The tayassuids, better known as peccaries or javelinas, once ranged as far north as the Yukon, but since the Pleistocene, they have not ranged north of Texas, New Mexico, and Arizona.  Feral swine, though, exist over large sections of the country, and wildlife and agricultural departments spend lots of time, money, and manpower on controlling their numbers.

Feral horses, though, get special privileges, as do feral donkeys.  They receive a certain amount of protection not afforded to other feral livestock in the Wild and Free-Roaming Horses and Burros Act of 1971. The horses and donkeys are not controlled in the same way feral pigs are. There is no continuous open season on them in the way that most states manage feral pigs.  Indeed, it is actually a crime to kill or harass feral horses or burros on federal land.  Excess horses and burros are managed through roundups, where some of them are deemed adoptable and sold to the general public.

For those of us with a modern ecological mindset, which has a deep disdain for making allowances for feral livestock, this law makes little sense.

But there is a sort of argument for this act. It goes something like this:

The modern horse species evolved in its current form in North America. Some taxonomists contend that there was once a Holarctic distribution of this species during the Pleistocene, and with the latest ancient DNA studies, I tend to agree with this assertion.

The North American population of horses became extirpated at the end of the Pleistocene, and when European horses went feral on the Western ranges, this constitutes a rewilding event.

Now, I don’t buy this argument very much, but I can say that there are some things we might consider. North America’s original population of cougars became extinct at the same time. The cougars that live in North America are derived from South American cougars that recolonized the continent about 2,000 years later.

Further, conservationists and sporting groups spend lots of resources on restoring and protecting elk populations. Elk have a much shorter history on this continent than horses ever did. Different experts have estimated when elk have first arrived. 40,000 years ago has been suggested, but more recent data points to them colonizing North America only 15, 200 years ago.

If elk arrived in North America only that recently, their status as native wildlife exists only as a weird  accident of geography. Elk are the on Cervinae or “plesiometacarpal deer” in the Americas. All the other deer in the Americas are Capreolinae or “telemetacarpal deer.”  Sika, axis, red deer, and fallow deer are also Cervinae, but they were introduced after colonization.

Elk don’t live in far northeast of Russia anymore. The elk of North America are the genetic legacy of this ghost population.

So the feral horse advocates could at least through the recent arrival of elk in North America as something to consider when we say their favorite animal is not native. Horses have a long evolutionary history in North America, and we just happen to be at an odd point of the history of horses that no native horses exist here. The earliest horse, Eohippus, first appeared in North America 52 million years ago.

So the feral horse advocates could say that we have a species that derived from a lineage that was here for over 50 million years that has now been restored through feral livestock and thus deserves these protections.  And this animal has at least as much rights to be free and roaming in North America as a large deer that had no connection to this continent until the latest Pleistocene.

However, the extinction of the horse in North America likely stemmed from natural climate change at the end of the Pleistocene.  Horses became extinct because they were poorly adapted to the new ecosystems, and as we have seen, horses really don’t do that well out in the deserts and semi-arid ranges of the West. They require water tanks to get them through long droughts, and they eat lots of forage. Not as much as domestic cattle, of course, but on ranges that are heavily catered toward livestock grazing, the horses are just an extra set of grazers that are taking away forage from native wildlife.

And even if we were to accept that horses were restored native wildlife, why on earth would we ever extend these protections to donkeys? Donkeys, though of ancient North American origin, evolved in their current form in Africa.

So although I do think of horses as no longer being native to North America, I do think questions of them being native or introduced are complicated, much more so than the question of feral pigs or cats. And yes, there is something like an argument that can be made for the native status of horses, even though I think it’s mostly in error.

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Changes in diet lead to changes in morphology and behavior:


These are precisely the same changes that have happened between wild and domestic Canis lupus populations.

Domestic variants are called Canis lupus familiaris.

In the same way that these lizards have evolved to eat vegetation, domestic dogs have new digestive adaptations to consume carbohydrates.

But these does not mean that new species have been created.

In the case of dogs and wolves, there has continued to be a small but not insignificant gene flow between wild and domestic populations. Black wolves in North America obtain their melanism from a mutation that was introduced into their population through breeding with domestic dogs, and now melanistic Italian wolves have been found to have exactly the same mutation that was also introduced in exactly the same way.

I don’t think dogs and wolves will ever become divergent enough to become distinct species, but I do think that smaller dogs, which are genetically isolated from the larger ones, could eventually evolve into a new species.

If there is no gene flow between the lizards on these two islands, they will also eventually become so genetically distinct as to lose chemical infertility.

I should also note that Dawkins hits the nail right on the head when he makes the caveat that we should not automatically assume that the lizards of Pod Kopiste haven’t also experienced rapid evolution as the ones on Pod Mrcaru. They could have indeed experienced similar rapid evolution, but the two would have derived from a common ancestor.

I think some of the problems in doing comparison research on dogs and wolves is that people are unwilling or unable to understand that this possibility exists.

There is an assumption that the wolves we are studying in captive situations are truly reflective of the ancestral population that gave rise to domestic dogs.

Most of these wolves are large wolves from northern Eurasia or northern North America.

It’s very unlikely that any of these wolves has contributed much genetic material to  modern dog populations.  North American wolves haven’t contributed much at all.

Further, most wolves in captivity descend from ancestors that were heavily persecuted by man.

What we’ve done is something like the Belyaev experiment in reverse. Whereas Belyaev selected for lack of fear in foxes, man has selected for something akin to paranoia in wolves.

We’ve trapped and poisoned them across the northern hemisphere.

The only ones that have survived, with the exception of some populations in the high arctic, have been those that have been most overly cautious. It’s well-known that many wolves won’t even cross highways, which stymies their recolonization of much of their former range, and in Yellowstone, at least one “Casanova wolf,” a bachelor wolf that mated only with the non pair-bonded wolves in established packs, used the highway as a buffer zone to keep from being killed by the main breeding male  in the pack.

The wolf that once ranged over the northern hemisphere couldn’t be like these animals. It had to have been much more adaptable and less timorous than these very reactive and fearful animals.

The ancient wolf had to have been an animal that was very easy to domesticate.

I’ve occasionally stolen from an insurance company’s advertisements when I’ve written about these issues, but I do think that dog domestication had to have been so easy a caveman could do it.

Modern wolves, in general, are difficult animals to tame. There are exceptions, and I’ve written about them at length on this blog.

But they are exceptions.

And just because some modern wolves have proven to be quite like dogs when socialized to humans doesn’t mean they are all appropriate pets.

It just means that the analogy that says dogs and wolves are as different as chimps and humans is false one.

You’ll never find a chimp that can do all the things that a human can do, but occasionally, you’ll find a wolf that is as tractable as any retriever or a dog that is as obstinate and reactive as any wolf.

Because some wolves are quite like dogs when they are imprinted and socialized with humans, I think it’s actually much more important to tell people not to keep them as pets.

Just because one tame wolf is as nice as a golden retriever doesn’t mean they all are. In fact, most are not.

But it’s not like the difference between humans and chimps.

It’s really the difference between wild and domestic.

I don’t know why it is that with this one domestic species very intelligent species spend hour after hour trying to deny the proper classification with its wild ancestor.

It’s almost creationist in a way.


I should also note the wall lizards have been introduced to southwestern Ohio. One of the members of the Lazarus department store family introduced a few lizards to the Cincinnati suburbs from Italy, and the wall lizards have expanded their range into adjacent Kentucky and Indiana.

Because they were introduced by a member of the Lazarus family, they are called “Lazarus lizards.”

I wonder if these lizards have any unique adaptations that separate them from the ones in Italy.




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This is a very good film. You have to love that vizsla.


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It is little secret that I have something that might be called outright contempt for feral cats.

I don’t necessarily hate the cats.

But they are essentially living pollution.

If a business released a chemical pollution that caused that much carnage among small wildlife as feral cats do, it would be fined out of existence.

I do not agree with nor do I support TNR. I also don’t support allowing owned cats to roam or to be left outside unsupervised.

I have lost subscribers, and I have lost links on blogrolls for having this position.

I don’t care.

The biggest weakness of the No Kill Movement is its adherence to TNR as a population control mechanism.

It doesn’t work. Indeed, it only works with fuzzy math.

Unfortunately, there is no solution for the feral cat problem other than trapping and euthanizing the adults and trying to capture and socialize the kittens that are young enough to be socialized to people. In rural areas, it should just be expected that landowners are going to shoot cats, especially if the cats are killing game birds or rabbits.

Most of the focus on feral cats on this blog have been a discussion about their impact to birds. It’s enough that cats cause $17 billion in  damages to bird populations each year.

But it turns out that the impact of cats on birds may be nothing compare to their impact upon lizards, frogs, and snakes.

A recent study of 60 free-roaming cats in the Athens, Georgia, area found that frogs, lizards, and snakes comprise 41 percent of their prey. 

The study was able to make these findings through attaching little cameras to the cats. The cameras recorded the cats’ activities, and they were able to find out what animals these cats were targeting on their nightly forays.

Only 12 percent of their targeted quarry wound up being birds.  They were mostly targeting either frogs, lizards, or snakes or small mammals (25% of their quarry).

This sort of makes sense.

Birds are damn hard to catch. Cats don’t fly, so they would have to be expert stalkers to get close enough to birds to make a kill.

They wouldn’t have the same problem targeting green tree frogs or Carolina anoles or cotton mice.

Now, we need a broader sample of free roaming cats to make generalizations, but if these trends apply across the continent, frogs could be in real trouble.

Well, even worse trouble.

We are currently experiencing a massive die-off of frogs.

Frogs are very sensitive to environmental changes, and many are dying off as the result of increased pollution and climate change.

The last thing they need is a large number of introduced predators targeting them.

And unfortunately, that’s what we’re getting with feral cats.

And also unfortunately, we have a feral cat cult that denounces any scientific evidence that shows that feral cats are to blame for endangering wildlife.

The arguments they tend to bring up are something in the vein of “Cats is cute” and “Your a monster.”

A few will point to a New Zealand study that found that cats kept down rats at a sea bird colony. When the cats were removed, the rat population shot up, and the birds suffered as the result of increased rat predation.

That’s an interesting find, but it does not mitigate all the birds that cats have killed off in New Zealand.

In fact, people who use that finding to denounce those who think feral cat controls are necessary are being intellectually dishonest.

To save biodiversity, the cats have got to go.

And there must be stricter laws on cat ownership– including laws that make it illegal to let them roam.

Dog people have dealt with those laws for a very long time. Cats are no more special than dogs. Why should cats be given carte blanche to wander around killing our native wildlife?

My stance may not be with some people, but those are the facts.

It’s also intellectually vapid to defend feral cats by saying that predators have colonized new areas for millions of years and have changed whole ecosystems through their colonization.

It is certainly true that predators have been colonizing new ecosystems throughout the history of life on this planet.

However, no introduced predator has been given the ability to colonize so many places as the feral cat has.

Cats have been introduced all over the world through trade.

Natural introductions of mammalian predators have almost always involved a land bridge. These introductions have been relatively uncommon– at least when compared to how cats and other introduced predators have been able to expand their ranges in the past 400 to 500 years.

Ecosystems usually have had time to adapt to during more conventional introductions.

These ecosystems really cannot handle such a rapid and expansive introduction as has been the case with feral cats.

Ultimately, I’ve not seen a single argument in favor of allowing feral colonies to exist that can’t be reduced to “Cats is cute” and “Your evil.”

Unfortunately, that’s the mentality we’re up against.


Thanks to Pai for posting this link on the blog readers’ group on Facebook!

See related post:

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Yeah, these pink things are baby fox squirrels (Sciurus niger).

A storm blew them out of a palm tree in Fremont, California, and they had to be hand-reared.

This is actually an introduced species to California, so there are some ethical concerns about hand-rearing this species for reintroduction into the wild.


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(NB:  Stoats are called ermine or short-tailed weasels in the United States and Canada.)

From The Independent:

In Britain, stoats are part of the rhythm of nature. They prey on rabbits and rats; they are preyed on by foxes and eagles. In New Zealand, whose only land mammals were two species of bats until Europeans arrived, stoats are the single biggest threat to the unique and increasingly threatened native birdlife.

A world leader in conservation, New Zealand has saved some of its rarest birds from extinction by ridding off-shore islands of predators. Stoats, which can swim, were thought to have a maximum range of 1.5 kilometres (less than a mile). Recently, though, the sleek, furry killers have turned up on an island more than five kilometres from the mainland, raising questions about the safety of offshore sanctuaries.

Many of New Zealand’s birds live and nest on the forest floor. Some, such as kakapo, weka and kiwi, are flightless. When they feel under threat, they freeze, making them easy prey for animals such as rats, cats and ferrets. Stoats – introduced in 1884 to combat a rabbit plague – are particularly formidable predators. They can tackle animals 10 times their body weight; they hunt by day as well as at night; they can travel vast distances, climb trees, and survive in almost any habitat. They are also prolific breeders, and they kill far more than they need to satisfy their hunger.

“When stoats get into a seabird colony or chicken hutch, they kill everything,” says Andrew Veale, an expert on stoat genetics at Auckland University. He cites credible reports of a moorhen being attacked by a stoat and taking off into the air, with the stoat still attached. Dr Veale says: “They are phenomenal killers, with an immense bite strength.”

More than 80 of New Zealand’s offshore islands are pest-free sanctuaries where all mammals have been removed through trapping, shooting, and dropping poison from helicopters. Last year, a stoat was found on Rangitoto Island, more than three kilometres off Auckland. The island had been declared predator-free only a year earlier, following a NZ$3m (£1.6m) eradication programme. By analysing the stoat’s DNA, Dr Veale established that it was from the mainland. This year, three stoats have been trapped on Kapiti island, a wildlife reserve 5.2 kilometres off Wellington. Dr Veale believes a female swam over and gave birth.

The destructive potential of stoats is well established. A single male killed 93 petrels on Motuotau island, in the Bay of Plenty, in four weeks. There have been instances of one or two stoats arriving on islands and wiping out entire populations. Philip Bell, a biosecurity officer with the Department of Conservation (DOC), said that if stoats could swim more than five kilometres, “there would be implications for the majority of islands around New Zealand”. He added: “A couple of stoats can create a breeding colony and wipe everything out. Stoats are arguably the biggest threat to our native bird species.”

They are also expensive. DOC has already spent more than NZ$200,000 trapping the three stoats on Kapiti. It will have to monitor hundreds of traps and tracking tunnels on the island for at least two years, as well as using dogs trained to detect stoats. No one is sure what prompts stoats to swim, although they appear to be in search of food. Dr Veale speculates that they take to the water after spotting land on the horizon. With the right tides, they could then travel considerable distances.

New Zealand’s first offshore wildlife refuge was established in 1891, on Resolution Island, off the South Island’s Fiordland coast. A decade later, stoats reached Resolution and killed off its kakapo population. However, more island sanctuaries followed, and kakapo were among the bird species rescued from extinction. Another bird, the Chatham Islands robin, was down to five individuals; but after being transferred to an island, the population recovered.

The stoats and ferrets (which were crossed with European polecats in order to make them more likely to survive in the wild) were introduced to control rabbits.

European rabbits were introduced so that they could be hunted as a game species, but New Zealand’s ecosystem was essentially predator free. Rabbits evolved with heavy predation pressure, and they are the archetypal r-selection species. Whenever one of these species is put into an environment where the pressures that forced them to evolve this reproduction strategy are absent, they very easily begin to overproduce.

However, the logic of introducing stoats or ferret-polecat crosses to control the rabbits appears to have been sound– until one actually applies it.  Rabbits evolves with mustelids attacking them, and they have ways of avoiding predation.  However, the ground-nesting birds of New Zealand evolved with virtually no ground predators, and they have no ways of avoiding mustelid predation.

Stoats and ferret-polecats are intelligent enough to know which species are more easy to hunt, so they go for the ground nesting birds over the rabbits.

So while they do attack and hunt rabbits, they have proved to be much more injurious to native New Zealand birds than to rabbits.

The only way to deal with stoats and ferret-polecats is to kill them.

It can’t be sugar-coated.

Either we cull the invasive species, or the endemic avian fauna of New Zealand is doomed.

But because these are pretty intelligent Carnivorans that are small enough to hide themselves easily, it might be impossible to kill them all.

And those that will remain will be the most wily little things, which will produce offspring that are even more cunning.

Over time, they could become even harder to control.

But even with that possible issue, these animals must be controlled now before the birds become extinct.



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They got only one cat.

These animals do have feelings.

However, they don’t belong on this continent.

The native fauna is ill-prepared to deal with their depredations.

And the only way to save many species of native Australian wildlife is to create areas that are free of foxes and cats.

The only way to do that is to kill them.

They shouldn’t be tortured when they are killed. A single killing shot will do.



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(The Steve Irwin reference is to the program that is being watched on the television in the background.)

This is a small Asian mongoose (Herpestes javanicus), which were introduced from Jamaica to control cane rats. The mongooses are not native to Jamaica either.

The mongooses on the Hawaiian islands are larger than those in Asia.  That’s probably because they are the only wild terrestrial predator in Hawaii, unless one wants to count feral cats.

They have been very bad for ground nesting native birds in Hawaii. The nēnē goose has suffered greatly from mongoose depredations, and controlling mongoose numbers has been key in protecting this species.

I first encountered a mongoose on Maui. I was sitting on the deck at the hotel where we were staying, when I noticed a squirrel-sized animal with bushy tail running between one copse of palm trees into the undergrowth. My mind registered it as a squirrel, but then I began to question that assumption. What was a squirrel doing in Hawaii?

As I watched the undergrowth for a little bit longer, the creature emerged, and there was no doubt that I was looking at a mongoose.



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This pacu was caught in the Hudson River near Albany, New York.

From the Albany Times-Union:

A South American fish sometimes called the “vegetarian piranha” got hooked by an angler in the Hudson River over the weekend, according to the state Department of Environmental Conservation.

The fish, called a pacu, is a cousin to the infamous flesh-eating predator, but instead eats plants and is not a threat to humans or other animals. It likely got into the river when someone dumped out the fish from a home aquarium.

Albany resident Steve Oathout said he was fishing off the Watervliet bike path Saturday evening when he caught the unusual flat fish, which was gray with a red underbelly. He took a picture and released the fish, which was about 16 inches long and weighed three pounds.

Reports to the DEC of pacus, which are widely available in aquarium shops, being caught in Hudson and Mohawk rivers average about one a year, DEC spokeswoman Lori Severino said.

The pacu looks similar to the piranha, but is larger and can grow to about the size of a turkey in its native habitat of Brazil. The pacu does not share the razor sharp teeth of its cousin.

But the piranha and the pacu have something in common — neither fish can survive the colder waters of upstate New York in the winter.

From my own forays into pet shops, I can tell you that pacus are much more commonly available than one might assume.

They are usually not regulated in the same way that the piranhas are, so a shop can sell them with little government oversight.

Of course, they get much larger than any species of piranha, and they quickly can outgrow their tanks.

I remember seeing a huge pacu in a 200 gallon tank at a pet shop in Parkersburg, West Virginia. I marveled at its size, but I was even more impressed with the 18-inch plecostmus that was resting along the side of the tank. I had two 4-inch plecos, and I had no idea they could reach such sizes. (I was but an ignorant child in those days, and the big pleco and my small ones may have been different species.)

But I see why it is not unusual for fishermen to catch pacus in North American rivers during the summer.

They outgrow their tanks, or in this bad economy, their owners are forced to get rid of their pets. There aren’t many fish rescues out there, so they pull an Joy Adamson. The dump their fish in the nearest large body of water.

Many fish have been introduced in this fashion, but with tropical species like the pacu, they aren’t going to do well in temperate climates during the winter.

But when they are released in tropical and subtropical rivers– which we have in this country– well, the results could be quite different.

Florida is full of bizarre introduced species. Hawaii is, too, but to a somewhat lesser degree. That’s because Hawaii has very strict import laws, and it’s a series of islands.

I’m not saying that Hawaii has no introduce species problems. It has plenty, but these are nothing compared to those of Florida.

Florida is connected to the rest of the states, where laws vary and different species are readily available. It is very hard to control which species are being brought into the state.

Because Florida is a much nicer place to be a pacu than upstate New York, it currently has a population of introduced pacus.

Winter keeps the pacus from taking the Hudson, but I think they are lucky that wels catfish aren’t widely available on the pet market in the United States.

This giant predatory catfish could easily colonize North American rivers– and they have been known to attack people!





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The nutria or coypu is a big wet (introduced) rodent!

I used to look forward to watching John Acorn’s The Nature Nut every day.

It used to be on Animal Planet at 6:30 AM, so I would make certain that I was ready to go by 6:30 every morning– just so I could watch it.

John Acorn is a Canadian entomologist centered in Edmonton, Alberta, but he covered a wide range of natural history topics on his show.  There was even a wonderful episode about how to think skeptically. That episode centered around the existence of bigfoot, and he gave a wonderful presentation on the principle of parsimony. He also did a show on how to care for various pet reptiles, which he said were the only pets he could have because of his allergies.

The show always featured a great comedic music video, which were in a class of their own!

One episode was about beavers. However, the take on beavers was quite different from anything else I remember seeing on the show. John Acorn created a holiday– Big Wet Rodent Day.  Big Wet Rodent Day was set up for July 26th, and during this day, we are to celebrate beavers and their role in Canada’s history.

The music video for that episode had a great Canadian patriotic song about the history of man and beaver in the northern part of North America. I wish I could find a copy of the song somewhere so you could hear it, but I have it stuck in my head.

However, I think that Big Wet Rodent Day should be international, and we should celebrate more big wet rodents than beavers.

Dave at the Little Heelers blog decided to feature the mountain beaver or Aplodontia on his Big Wet Rodent Day post. Mountain beavers are big and wet not because they are aquatic but because they live in temperate rainforests.

In that same spirit, I think I’m going to celebrate another big wet rodent, but mine is an aquatic rodent. However, mine is not native to North America or Europe, but it has been introduced there.  They have even been introduced to parts of Africa.

The creature I’m talking about is most accurately called a coypu, and it is a large aquatic rodent native to southern South America. It has a long, rat-like tail, and it might be confused with a large muskrat. However, unlike the muskrat, which actually is closely related to rats and mice, the coypu is a Caviomorph rodent. Its closest relatives are the capybara and the various cavies (guinea pigs).

The coypu was introduced to North America as a fur-bearer.  The fur industry sold the fur as “nutria,” which is Spanish for otter, and the name has stuck with it. The market for its fur collapsed rather quickly, and these animals were released into the wild. They are now found in many states in the United States and in parts of Canada, but they are perhaps most numerous in the state of Louisiana. In Louisiana, the “tabasco rat” has worked  its way into Cajun table fare. From my sources in Louisiana, this animal is heavily hunted, but hunting has done very little to control its numbers.

So on this Big Wet Rodent Day, remember the nutria or coypu. It may be an invasive species, but it’s got some very wicked orange teeth.



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