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Singing Snails and Killer Whales: Parallels in Conservation

The views expressed are those of the author and are not necessarily those of Scientific American.


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Figure 1: Molokai Tree Snail in a native Hawaiian Ohia tree.  Photo by David Sischo

Figure 1: Molokai Tree Snail in a native Hawaiian Ohia tree. Photo by David Sischo

According to ancient Hawaiian legend, the snails here sing in the trees at night. There are over 30 traditional Hawaiian songs and chants that mention tree snails. Much of the cultural knowledge of Polynesian people was passed on through song, and the fact that these animals were frequently mentioned shows us how important they were (let’s see you try keeping a 300 year old book in top condition in the tropics). And yet, many people living and visiting Hawaii today don’t even know they exist. I’m a big fan of seeing things that most people have never heard of, so when my friend David Sischo asked if I would like to help him hunt for singing snails in the forests of Molokai, I jumped at the opportunity.

How did snails even get to Hawaii in the first place? It doesn’t seem like the best idea; a snail’s skin is so permeable to liquids and salts that if it tumbled into the ocean, most of the water in its body would flow out through its skin until it would shrivel up like a tiny, sad little raisin. The Hawaiian Islands are the most isolated island chain on earth, surrounded by more than 2000 miles of ocean, and yet there are land snails. Researchers think that the first Hawaiian Land Snails arrived on Oahu about 3.7 million years ago. They were not large tree snails like the ones we find in Hawaii today, but were probably millimeters long.

Figure 2: This tiny snail, in the same family as the larger tree snail, is probably similar in size to the first snails to arrive in Hawaii. Photo by Alexis Rudd.

Figure 2: This tiny snail, in the same family as the larger tree snail, is probably similar in size to the first snails to arrive in Hawaii. Photo by Alexis Rudd.

These snails probably arrived clinging to the feathers of birds, or possibly blown across the ocean in a hurricane, clinging to a leaf. They may have even clung to a floating stick, precariously rafting across the dangerous salt sea. Since their arrival, the Hawaii tree snails have evolved to about the size of the first joint of your thumb. They live in rare ohia (oh-hee-ah) trees, where they eat fungus and mold off the leaves. Unlike the snails that pester gardeners, these tree snails may actually be helping the trees by removing gunk and grime from the leaves where photosynthesis and gas exchange occur.

David, a Ph.D. student at the University of Hawaii, studies a species of tree snail that lives on the Island of Molokai, which is directly south of Oahu. Molokai is famous for its high mountains and sea cliffs, and getting to the snail populations can be a huge challenge. Sometimes these populations can only be reached by helicopter, but Dave had information that the population we wanted to get to was “easily accessible” and that the road “looked really good.” So we hopped in our rental jeep and headed up the mountain.

If a person from Molokai ever tells you that the roads are looking good, all I can say is that you should make sure you bring a shovel. And maybe a pickaxe, spare (full-size) tire, and some large pieces of plywood to place over the giant ditches you will inevitably encounter. Reading in the car is right out, and make sure to finish your Dr. Pepper before you get going, or it will be splashed all over your lap. The road to Dave’s field site was approximately 3 miles long, but it took us over two and a half hours to drive, including an hour-long stop for road repair where we carried rocks and small dead trees up a steep hill to fill some especially deep ditches.

Figure 3: Rats chewed holes in these tree snail shells and ate the snails. Photo by Nathan Yuen at http://hawaiianforest.com

Figure 3: Rats chewed holes in these tree snail shells and ate the snails. Photo by Nathan Yuen at http://hawaiianforest.com

We stopped the car about ¾ mile from the hunting cabin where we would spend the night, and hiked the rest of the way through a thick swamp. According to Dave, the cabin used to be infested with Ratatouille-esque rats that would spend their nights sliding down the broomstick and dancing on our faces. Fortunately, we had brought a rat-eradication expert with us, who quickly plugged up the rat-sized holes.

The snails aren’t so lucky. There are many compelling threats to island species, but rats and other invasive species are one of the worst offenders. Almost all of these invasives were brought here by humans: rats came on ships, malaria-bearing mosquitoes came in cargo, and carnivorous wolf-snails were purposefully brought here to control another invasive snail, but learned that native tree snails were easier to catch.

Animals that live on islands tend to spend less time defending themselves from predators. From an evolutionary viewpoint, this makes sense – why should an albatross spend valuable energy guarding against nonexistent foxes, when it could spend that energy on finding food for its chick? Thousands of years of safety from predation have led to the loss of anti-predation measures in these species, leaving them vulnerable to human hunters or introduced predators.

On the mainland, snails generally lay many eggs so that a few of their offspring will survive the rats and other predators. In Hawaii, snails actually give live birth to a few baby snails each year. This type of evolutionary strategy gives them an advantage in a predator-free environment, because it means that each baby snail is stronger and bigger when it enters the world. Hawaiian tree snails don’t start reproducing until they are five to seven years old. Normally, this would be an advantage, because it would give them time to get nice and big so they could produce nice, big, healthy baby snails.

Figure 4: Molokai Tree snail looking out over the fractured habitat of the meadow. Photo by David Sischo.

Figure 4: Molokai Tree snail looking out over the fractured habitat of the meadow. Photo by David Sischo.

But with rats around, few snails make it through the gauntlet to adulthood. Even once they’ve made it, so few snails are still around that it is difficult to find a mate – or, at least a mate who isn’t related to you. As David is finding, many of the snails are badly inbred, which makes them more susceptible to genetic disease and less able to adapt to change.

On this trip, David wanted to collect snails from the continuous forest surrounding what he calls “snail meadow.” Snail meadow is a grass meadow created about 100 years ago, when cows were pastured in the area. Most of the native trees in the area are gone, leaving scattered native Ohia trees. For a snail, each Ohia tree might as well be an island; the snails on these trees have been inbreeding for about as long as the meadow has existed. Dave thinks that the snails in the forest around the meadow may be less inbred, because they can crawl from tree to tree to find a mate.

The first day we spend searching for snails in the forest is extremely frustrating – we only find five snails in four hours. All of us searchers are extremely worried about our snail-hunting skills. Finding a snail is an amazing experience. Each one is different, and the patterns on their shells are elaborately beautiful. In fact, they used to be killed by the thousands for their decorative shells, which people used as jewelry and decoration. Even scientists contributed to this decimation, as naturalists killed thousands for their collections. Personally, this scientist prefers them alive, to watch how they move and interact with their world. The second day is a little better, but not much, so we decide to have an early dinner and try hunting snails by moonlight (and headlamp).

Figure 5: David searches the trees for snails as the sun sets over Molokai. Photo by Andrew Titmus.

Figure 5: David searches the trees for snails as the sun sets over Molokai. Photo by Andrew Titmus.

We have the best luck at this – the snails are generally on the underside of the leaves, and their shells reflect white in the light of our headlamps. It is too bad that the snails don’t sing, because it would be a lot easier to find them. Searching for snails in the pitch black, we have no idea where the path of least resistance is, and end up burrowing through bushes and wading through hip-deep ferns that grab our legs like some monster plant out of Harry Potter. I get in trouble more than once for bringing up The Blair Witch Project and giving everyone the creeps.

After 80 man-hours of searching night and day, we come up with 40 snails in the forested area, a frustratingly low number compared to previous trips. Dr. Mike Hadfield, who has been studying snails in this meadow for 20 years, used to find hundreds of snails in the meadow trees. When I ask Dave why we’re finding so few snails, he says that it may be because rats are controlled in the meadow, but not in the forest. As a result, forest snails can move around but are more likely to be munched by rats. Then he goes on to drop a bombshell: not only is there little likelihood of extending the rat control to the forest, they probably won’t be able to keep the rats out of the meadow for much longer. Funding cuts mean it’s just not likely to happen. “We might be the last people to see this species,” Dave says.

I ask him how this is possible – isn’t it illegal to stop protecting an endangered species? Dave explains that this species of tree snail isn’t listed as endangered, even though its life history and predation pressures are the same as a protected sister species on Oahu. Listing a species under the endangered species act is actually quite difficult; in order to list a species, scientists have to designate their “critical habitat.”

The problem with this is that, for many species, there is limited or no information about their critical habitat. It took four people three days of hard work to find forty snails in a quarter mile area – can you imagine how long it would take to determine the limits of the snails’ range? And after that, to do multiple surveys over time to monitor whether the population was shrinking? This isn’t only a problem for small, relatively unknown animals like snails. Killer whales, one of the most popular of the charismatic megafauna, have had the same problem.

Figure 6: Southern Resident Killer whale critical habitat had to be determined before anything could be done to protect them under the endangered species act. Photo taken under Cascadia Research’s NFWS Permit # 540-1811 by Alexis Rudd.

Figure 6: Southern Resident Killer whale critical habitat had to be determined before anything could be done to protect them under the endangered species act. Photo taken under Cascadia Research’s NFWS Permit # 540-1811 by Alexis Rudd.

The Southern Resident Population, which spends some of its time in and around the Puget Sound of Washington, is declining rapidly. Although we know quite a lot about what they do when they’re in the Puget Sound, once they leave the Straight of Juan De Fuca (which separates Washington State from Vancouver Island, we don’t really know very much about what they do. As of a 2006 report, there had been only 26 sightings of this population in 30 years outside of the Straight.

Scientists had to figure out where they spent that time before endangered species law could protect the whales. Unlike snails, killer whales already have some protection under federal law under the Marine Mammal Protection Act. Regardless of a species’ charisma and popularity, the responsibility is on conservationists and scientists to prove that it needs protecting. If there is no will or no money available to do the research to prove these species need protection, they may decline without ever going on the endangered species list. In fact, the majority of species that became extinct in the first 21 years after the Endangered Species Act were never listed as endangered. There is no legal requirement to protect the tree snails of Molokai, and there is no money to keep the rats from snacking on them like the Belgian chocolates they resemble so much.

On the ride back down the mountain, the transition between the areas protected from goats and the unprotected areas is apparent. I see my first endangered Williwilli tree – a tree that truly looks like it came from a Dr. Seuss book. The snail crew is quieter on the way back, tired out from three days of peering through leaves and fixing roads. Even though we’re exhausted, I feel truly privileged to have seen the singing snails of Molokai. I hope that I will see them again someday – alive and sliming.

Happy and sliming

Happy and sliming

Alexis Rudd About the Author: Alexis Rudd is a graduate student at the University of Hawaii, where she spends her time using underwater sound to learn about the distribution and behavior of dolphins and whales. Her interests also include acoustics and seabird biology. She received her B.S. in Biology at the University of Puget Sound. When she’s not being a student, Alexis enjoys snorkeling, hiking and photography. Alexis blogs about whales, dolphins, sound and the sea at Sounding The Sea. You can also follow her on twitter @SoundingTheSea Follow on Twitter @SoundingTheSea.

The views expressed are those of the author and are not necessarily those of Scientific American.






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