The Chickens of Kauai

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If there’s a soundtrack to the Hawaiian island of Kauai, it’s not waves or the songs of a native bird or even hula music — it’s the crow of the cock. Everywhere I’ve been on Kauai, from the beach to the town to the mountains, there have been chickens.

The chicken population on the island exploded more than 20 years ago, after Hurricane Iniki, which devastated several Hawaiian islands. On Kauai, one of the lesser effects was that the storm blew apart chicken coops — possibly many housing fighting chickens — and released the birds into the wild. It’s not all that surprising that the birds then thrived because their wild ancestor, the red jungle fowl, lived at similar latitudes in Southeast Asia.

(You might think that all those chickens would be a great source of food for the local people, but I’ve been told that the birds are hard to catch. Chickens can see and keep track of four things at once — up and down and with each eye — so it’s hard to sneak up on one. Plus, the meat is tough. I suggested to one local that he try coq au vin — the traditional French method of cooking an old bird — but he looked at me like I was nuts. I still maintain, though, that even if it’s not a local dish, cooking a chicken in lots of wine, and maybe some garlic, would sure be tasty.)

Chickens are just one of the non-native species that have spread across Kauai, and one of the less destructive ones. I visited with Diane Ragone, head of the Breadfruit Institute, this week, and she noted that while most people look at this island and see nothing but lush green mountainsides, she sees lands bare of native plants. And then there’s all the invasive animals. I found a couple of adorable young feral cats at the end of the road (literally) on the North Shore of the island and winced when a woman started feeding them. I don’t want kitties to die, but they are a huge problem on islands like this one because they kill native birds. And here there are some spectacular birds, such as Laysan albatrosses and red-footed boobies. Feral pigs now roam the island, causing all sorts of damage. There’s even deer that have been purposely released so people can hunt them. There’s a flock of parrots that derive from someone’s lost pets.

One of the things that has struck me since I’ve been here is how most tourists will never realize that the island has changed dramatically in the last couple of hundred years, since the first Europeans arrived and began introducing all these non-native species. Kauai is beautiful now and truly lives up to its nickname as the “Garden Island,” but what must it have looked like before all of this changed?

Photo by the author

Fire Versus Crazy: Battle Of The Invasive Ants

Fire_ants02There’s a good chance you’ve heard of the red imported fire ant (above), a pest that’s found across the southern half of the U.S. and is now one of the world’s 100 worst invasive species. These aggressive ants, natives of South America, not only have a painful sting but also a penchant for attacking in swarms.

Less known is the Caribbean crazy ant, a more recent invader that’s been found in Florida and Texas (where it was once called the raspberry crazy ant). Unlike fire ants, Caribbean crazy ants — named for their erratic behavior — don’t have stingers and hardly bite. But infestations can be huge and incredibly hard to control. In one story from 2008, a woman describes how she kept killing and killing the ants that swarmed her house and within a week had filled a five-gallon bucket with dead ants.

News reports sometimes say that Caribbean crazy ants will attack and drive out fire ants, but there hasn’t been any scientific data that backs up the claims. So a trio of biologists from Rice and Texas A&M universities staged battles between nests of the two species. Their study appears in PLOS One.

The bad news is that, while there was no outright winner in the ant-on-ant combat, the crazy ants came off the worse of the two species; crazy ants were twice as likely to die as fire ants. It seems that the fire ants may be better equipped for a war, the scientists say. The fire ants are armed with stingers, which may be a more effective weapon than the crazy ants’ ability to spray formic acid. “It is possible that the ability to sting makes fire ants a more potent combatant than crazy ants,” the researchers write.

One odd thing that the scientists discovered is that crazy ants get more aggressive when they’re fed a low-carb diet. They even do better in battle and die less often when fighting fire ants. That’s different from most other ant species, which get more aggressive when given high-carbohydrate food. But what that means for which species wins out and spreads its misery farther, well, we’ll just have to wait and see.

Image courtesy of USDA/ARS via wikimedia

Cow Patties May Have Helped A Toxic Toad Invade Australia

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The center of Australia, is a dry, hot, unforgiving landscape, but the edges of the continent are more diverse, with beautiful wooded mountains, lush rainforests and thriving cities. And farms. Lots of farms. About half of Australia is, in fact, covered in land used for grazing livestock (though I should note that some of that grazing does take place in rather harsh areas of the interior as well as nicer bits closer to the coasts). Like many lands around the world, Australia has been incredibly altered by humans.

Altering landscapes often facilitates the spread of non-native species, letting them become invasive pests. The phenomenon is best known among invasive plants, like purple loosestrife, but it seems to hold true for some animals as well, like the cane toad in Australia.

Cane toads, natives of South America, are a big problem in Australia. They first arrived in Queensland in 1935, deliberately brought to the country to help keep beetles in control to improve sugar yields. That plan didn’t pan out, and the toads quickly began to spread across the country. One more amphibian in the landscape might not seem like a huge problem, but cane toads secrete a toxic poison that kills most anything that eats them, even crocodiles. As cane toads have spread, they’ve devastated populations of many native Australian animals.

I first got interested in the cane toad when I blogged about a study in which scientists successfully taught cute critters called quolls to not eat the toads by feeding young quolls young toads (not yet poisonous) laced with a chemical that made the toads taste bad. And then last year, I got a chance to meet the mastermind behind the study, University of Sydney herpetologist Rick Shine, who I profiled in Science magazine. Shine became one of the leading cane toad researchers in Australia after the toads invaded his long-term research site outside Darwin.

In one of his more recent studies, published last November in PLOS ONE, Shine’s group looked at how cow patties might help cane toads survive the hot, dry Australian summer. Members of the group had noticed that toads could often be found on or near cow patties, and they wondered whether the amphibians were indeed more likely to hang out there.

The researchers walked transects set up on a farm located near their research site, recording the locations of both cane toads and cow patties during the dry season. Seventeen of the 26 toads they found were sitting on cow patties, and the remaining nine were fairly close to the piles of poo.

“Toads were found on cowpats more often than expected by chance, and toads that were not on cowpats were closer to them than would be expected by chance,” they write in their paper.

The cow patties, the researchers surmise, provide both a moist environment and food, in the form of dung beetles, which helps the cane toad survive the harsh Australian dry season.

Cane toads are already known to take advantage of water sources, like ponds, set up to supply livestock. Add in the continent’s 300 million cow patties deposited each day — that’s 28.5 million cattle each producing 12 cow patties per 24 hours — and livestock grazing has obviously provided the cane toads with a friendly environment that has helped them spread. Humans have tamed much of Australia to make it more liveable for themselves, but they also made it more liveable for cane toads.

Cane toad image courtesy of flickr user blundershot

An Invasive Crab Is Helping Cape Cod’s Marshes To Recover

crabInvasive species are generally not good for an ecosystem. Zebra mussels, snakehead fish, feral hogs, nutria, domestic cats, purple loosestrife — I could probably fill inches of your screen with the names of species that have caused havoc when moved into a new landscape. But not all species prove troublesome when transported out of where they are traditionally found, and now there’s a case where an invasive crab is actually helping an ecosystem to get healthier.

The case comes from Cape Cod, where overfishing has removed most of the predators from the salt marshes. Without those predator species to keep it in check, the crab Sesarma reticulatum has grown in numbers. The species denudes the marshes of the cordgrass that holds the land together, and also burrows into the ground, making that soil more susceptible to erosion.

In recent years, though, some of those marshlands have started to recover, and the cordgrass began to return. That recovery can be tied to the arrival of another crab, the European green crab (Carcinus maenas), say researchers from Brown University in a study in Ecology.

“When we started seeing the marshes recover, we were baffled,” study coauthor Mark Bertness said in a statement. “To see very quickly the marshes start to come back, at least this veneer of cordgrass, it seemed pretty impressive. When we started seeing this recovery we started seeing loads of green crabs at the marshes that were recovering. We went out and quantified that.”

The researchers looked for crabs in healthy and recovering marshes. There weren’t many green crabs in the healthy marshes, and there also weren’t many¬†Sesarma burrows in those areas. But in recovering marshes, there were lots of burrows and lots of green grabs using them.

They then tried an experiment, putting a Sesarma crab and a green crab in a cage near a burrow. The green crab not only took over the burrow, but it often killed the other crustacean. In another test, they caged the crabs in a plot of grass. When a Sesarma crab was on its own, it would eat a lot of grass, but when it had a companion of the other species, it was put off its feast, even when the green crab was restrained from attack.

What’s happening in these recovering marshes, the researchers say, is that the green crabs are finding refuge from predators and the sun in the burrows of Sesarma crabs, and then feeding on the Sesarma crabs. Those crabs are not only getting reduced in numbers through this competition and predation, but they’re also reducing their cordgrass destruction because they’re afraid of the green crabs.

“Non-consumptive effects can be much more powerful because whereas a consumptive effect is one crab eats another crab, a non-consumptive effect is one crab scares dozens of crabs,” Bertness said. “The ecological effect can be much greater much quicker.”

The result is that the cordgrass in those recovering areas is getting the chance to grow back. And when the grass recovers, other species may follow.

The researchers — and I — called the green crab an “invasive species” but that’s probably not right in this context. The definition of an invasive species is “an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.” The green crab may be an alien, but we probably need another term for one that causes an environmental benefit.

Image (a European green crab) credit: Catherine Matassa/Northeastern University