It is a scene that has played out countless times across the swamps and wetlands of northern Australia: A family of feral pigs goes down to the water’s edge to drink.
Just when the pigs are at their most vulnerable, a member of the world’s largest crocodile species erupts from its camouflage in the water, sending piglets flying in a ferocious display of teeth and power. Even an adult pig, which can weigh up to 150 pounds, doesn’t stand a chance.
“Crocodiles eat whatever is easiest, and feral pigs are the perfect size,” said Mariana Campbell, a researcher at Charles Darwin University in Australia who studies saltwater crocodiles in the country’s north. “They’re pretty lazy hunters. If you’re a crocodile, what is easiest? You stay near the bank and wait a few hours for a pig? Or you go and hunt for a shark, an animal that can swim five times faster than you?”
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Frank Mazzotti, a crocodile and alligator expert from the University of Florida, agreed.
“A pig coming down to the water’s edge is like ringing the dinner bell,” he said.
Some scientists hope that the encounters between the crocs and the swine may be the first sign that the feral pig, an invasive species that has done great damage to Australia’s wild terrain, has finally met its match. The instances may also help to explain why crocodiles are doing so well, according to a recent study Dr. Campbell and other researchers published in the journal Biology Letters.
The saltwater, or estuarine, crocodile has lived for millions of years in Australia. The feral pig arrived in Australia with the first European settlers in the late 18th century. One is Australia’s largest apex predator that came close to extinction in the early 1970s. The other has spread across close to 40 percent of Australia’s land mass, and conservative estimates suggest that there may be 24 million in the country. Scientists blame feral pigs and other invasive species for widespread habitat loss and for Australia having the world’s highest rate of mammal extinctions.
As divergent as their evolutionary paths may appear, the interplay between the saltwater crocodile and the feral pig, between predator and pest, may be rewriting the complicated story of what happens when nonnative species take over an ecosystem. Whatever ecological destruction invasive species cause, the relationship between hungry crocodiles and voracious pigs in Australia highlights the unexpected cascades in nature brought about by invasive species. Similar surprises are being observed in Florida and elsewhere in the United States, where conservationists and wildlife officials must factor invasive species into their attempts to preserve local animals.
To understand whether unsuspecting pigs were helping to restore the Australian crocodile population, Dr. Campbell and her colleagues studied the carbon and nitrogen isotopes taken in recent years from bone samples of crocodiles dwelling in Darwin Harbor and Kakadu National Park. They then compared these to museum samples that had been taken from all across Australia’s Northern Territory between the late 1960s and the mid-1980s.
“The bones retain a signature that remains across the life of the animal. If you want to look at an animal’s diet in the short term, you look at blood and plasma,” Dr. Campbell said. “If you want something a little further back, you would look at collagen or skin. For long term, you look at bones.”
The bone analysis revealed that over the past 50 years, feral pigs became the crocodile’s primary food source. This marked a fundamental shift in the diet of Australia’s oldest predator species to terrestrial species from mostly aquatic prey. “We expected to see some difference in the diet,” Dr. Campbell said. “But we were amazed by the difference between what they were eating back then and what they are eating now.”
The story of the saltwater crocodile and the dietary change that drove its recovery began in 1971, when the Northern Territory government banned crocodile hunting. Toward the end of World War II, there had been around 100,000 saltwater crocodiles. By 1971, there were barely 3,000, and the species was in danger of extinction.
In the decade after the hunting ban, a culling program significantly reduced the numbers of wild buffalo, another invasive species. This in turn expanded the ecological niche available to feral pigs. Smaller and more shy than buffaloes, the pigs were much more difficult to cull, and their population grew rapidly. In greater numbers and with a broader range, they became a ready food source for crocodiles.
There are now an estimated 100,000 wild saltwater crocodiles in the Northern Territory, and, Dr. Campbell said, “if it wasn’t for the availability of feral pigs in the environment, the population wouldn’t have recovered to the same level that they have.” The study noted that the recovery in saltwater crocodile numbers has been slower in areas where there are no feral pigs and where no dietary shift could occur.
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Dr. Campbell acknowledges that more research is needed to understand whether predation by saltwater crocodiles is having any impact upon the overall feral pig population. But the early signs are promising.
“We believe that crocodiles are making a difference by creating barriers to movement by the feral pigs,” Dr. Campbell said. She added, “You can imagine: If you are a pig in the Northern Territory, you probably wouldn’t try and swim across the Mary River because you won’t get to the other side.”
The study of Australian saltwater crocodiles is among the first to confirm that apex predators can benefit from large populations of invasive prey species. Scientists around the world had long suspected similar relationships.
Just when the pigs are at their most vulnerable, a member of the world’s largest crocodile species erupts from its camouflage in the water, sending piglets flying in a ferocious display of teeth and power. Even an adult pig, which can weigh up to 150 pounds, doesn’t stand a chance.
“Crocodiles eat whatever is easiest, and feral pigs are the perfect size,” said Mariana Campbell, a researcher at Charles Darwin University in Australia who studies saltwater crocodiles in the country’s north. “They’re pretty lazy hunters. If you’re a crocodile, what is easiest? You stay near the bank and wait a few hours for a pig? Or you go and hunt for a shark, an animal that can swim five times faster than you?”
Advertisement
Continue reading the main story
Frank Mazzotti, a crocodile and alligator expert from the University of Florida, agreed.
“A pig coming down to the water’s edge is like ringing the dinner bell,” he said.
Some scientists hope that the encounters between the crocs and the swine may be the first sign that the feral pig, an invasive species that has done great damage to Australia’s wild terrain, has finally met its match. The instances may also help to explain why crocodiles are doing so well, according to a recent study Dr. Campbell and other researchers published in the journal Biology Letters.
The saltwater, or estuarine, crocodile has lived for millions of years in Australia. The feral pig arrived in Australia with the first European settlers in the late 18th century. One is Australia’s largest apex predator that came close to extinction in the early 1970s. The other has spread across close to 40 percent of Australia’s land mass, and conservative estimates suggest that there may be 24 million in the country. Scientists blame feral pigs and other invasive species for widespread habitat loss and for Australia having the world’s highest rate of mammal extinctions.
As divergent as their evolutionary paths may appear, the interplay between the saltwater crocodile and the feral pig, between predator and pest, may be rewriting the complicated story of what happens when nonnative species take over an ecosystem. Whatever ecological destruction invasive species cause, the relationship between hungry crocodiles and voracious pigs in Australia highlights the unexpected cascades in nature brought about by invasive species. Similar surprises are being observed in Florida and elsewhere in the United States, where conservationists and wildlife officials must factor invasive species into their attempts to preserve local animals.
To understand whether unsuspecting pigs were helping to restore the Australian crocodile population, Dr. Campbell and her colleagues studied the carbon and nitrogen isotopes taken in recent years from bone samples of crocodiles dwelling in Darwin Harbor and Kakadu National Park. They then compared these to museum samples that had been taken from all across Australia’s Northern Territory between the late 1960s and the mid-1980s.
“The bones retain a signature that remains across the life of the animal. If you want to look at an animal’s diet in the short term, you look at blood and plasma,” Dr. Campbell said. “If you want something a little further back, you would look at collagen or skin. For long term, you look at bones.”
The bone analysis revealed that over the past 50 years, feral pigs became the crocodile’s primary food source. This marked a fundamental shift in the diet of Australia’s oldest predator species to terrestrial species from mostly aquatic prey. “We expected to see some difference in the diet,” Dr. Campbell said. “But we were amazed by the difference between what they were eating back then and what they are eating now.”
The story of the saltwater crocodile and the dietary change that drove its recovery began in 1971, when the Northern Territory government banned crocodile hunting. Toward the end of World War II, there had been around 100,000 saltwater crocodiles. By 1971, there were barely 3,000, and the species was in danger of extinction.
In the decade after the hunting ban, a culling program significantly reduced the numbers of wild buffalo, another invasive species. This in turn expanded the ecological niche available to feral pigs. Smaller and more shy than buffaloes, the pigs were much more difficult to cull, and their population grew rapidly. In greater numbers and with a broader range, they became a ready food source for crocodiles.
There are now an estimated 100,000 wild saltwater crocodiles in the Northern Territory, and, Dr. Campbell said, “if it wasn’t for the availability of feral pigs in the environment, the population wouldn’t have recovered to the same level that they have.” The study noted that the recovery in saltwater crocodile numbers has been slower in areas where there are no feral pigs and where no dietary shift could occur.
Advertisement
Continue reading the main story
Dr. Campbell acknowledges that more research is needed to understand whether predation by saltwater crocodiles is having any impact upon the overall feral pig population. But the early signs are promising.
“We believe that crocodiles are making a difference by creating barriers to movement by the feral pigs,” Dr. Campbell said. She added, “You can imagine: If you are a pig in the Northern Territory, you probably wouldn’t try and swim across the Mary River because you won’t get to the other side.”
The study of Australian saltwater crocodiles is among the first to confirm that apex predators can benefit from large populations of invasive prey species. Scientists around the world had long suspected similar relationships.
Pigs to the Rescue: An Invasive Species Helped Save Australia’s Crocodiles
Invasive species can damage the ecosystems they wind up in. But in parts of the world, endangered predators make hearty meals out of them.
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