Category Archives: Mammal

Predatory Life On The Savanna Is Complicated (Unless You’re A Lion)

lions

In a simple system, there’s a predator and its prey; the predator roams wherever the prey is found. Add in more predator and prey species, and where the predators live should be decided by what they eat. Real life, though, is not that simple. Just look at this new study published online by Ecology of four predator species in South Africa.

An international group of researchers studied an 85-square-kilometer, fenced-in region of South African savanna — the Karongwe Game Reserve. In this area there are four main predator species: lions, cheetahs, leopards, and wild dogs. These predators hunt 12 different ungulate species, mostly impala, blue wildebeest, waterbuck, Burchell’s zebra, warthog, and giraffe.

To figure out where the predators were going and what they were doing, many of the adults of each of the four species were outfitted with VHF transmitters during the study period of 2001 to 2005. The distributions of the prey species were determined by aerial surveys and sampling in the wet and dry seasons (respectively, November to March and April to October).

All that data was then combined. The patterns and interactions of the various species are complex, but there were definite patterns:

Lions: The big cats (above), as might be expected, are the dominant predators in this environment. That power gives them unrestricted access to pretty much anything they want. They go where the best and most vulnerable prey can be found and where they’ve got the best cover for hunting. They don’t worry about where other predator species are. Even the season doesn’t affect them much.

Leopards: These cats overlap in range with lions — the best prey is found where the lions live — but they avoid the much-bigger cats. They also avoid each other. In this area at least, the biggest killer of leopards is other leopards. And during the dry season, when it’s easier to see through parched vegetation and the risk of detection by other cats is higher, leopards find it safest to move towards the smaller wild dogs.

cheetah

Cheetahs: Like leopards, these spotted cats (above) are also smaller than lions, and it would be expected that they would also avoid the big cats. But, like the leopards, their range overlaps with the lions. And in the wet season, these cats tended to actually move towards locations where lions were recently roaming. The researchers theorize that cheetahs may be using other tactics to avoid lions, such as by choosing habitats, like woodlands, that the bigger cats don’t use, or being active when lions aren’t. Staying near the lions, and their high-quality prey, proved beneficial; some cheetahs were able to take down large prey like wildebeest instead of having to stick with smaller meals. But just because the cheetahs were comfortable venturing into lion territory doesn’t mean that they were entirely fearless; these cats generally stayed away from leopards.

Wild dogs: The African wild dogs — the smallest of the predators — tended to avoid all three of the cat species, but they behaved differently depending on the season. In dry times, when they could be more easily seen, the wild dogs stayed away from the other carnivores’ activity centers. In the wet season, though, when there was more cover available, they took a little more risk and only avoided areas where the other species had been recently. Constrained as they were by the movements of the other predators as well as the boundary fence they could not cross, the wild dogs had to settle for prey species they did not prefer.

The researchers’ take-away message from all these interactions is that for subordinate carnivores like the cheetahs, leopards, and wild dogs, competition with other predators can matter more than what they eat. Because if you have to eat an impala instead of a wildebeest, or even wait another day for a hearty meal, being hungry is better than getting mauled to death by another predator.

Images courtesy of flickr user Jean-Louis A

June 4, 2013Permalink Leave a comment

Tiger, Tiger, Brilliant White

tigersWhite tigers, despite the name, aren’t all white. These variants of the Bengal tiger are white with black or dark brown stripes, and they also have blue eyes, pink paw pads and a pink nose. They’re not true albinos, but they’re rare. Really rare. As in, none have been seen in the wild since 1958. All the known white tigers in the world live in captivity, usually zoos.

What strips the orange stripes out of these tigers? A team of researchers led by Xiao Xu of Peking University in Beijing, reporting this week in Current Biology, examined tiger genes and found that a single amino acid change — a simple switch of one chemical piece of a protein — resulting from a mutation in the gene SLC45A2 is responsible for the white color. When a tiger has two copies of that mutated gene, it can’t produce the pigment pheomelanin that gives the cat its orange fur.

Alterations to that gene underlie similar color changes in cream-colored horses and silver chickens. The same mutation in the gene has even been found once in a human, in a German who had pale skin and dark blonde hair.

The researchers think that the mutation, which they unsurprisingly named white, evolved just once in the wild Bengal tiger population. That mutation slowly spread through the tiger’s descendents and created the occasional white tiger. The animals were spotted infrequently in India from the 1500s until 1958, when the last wild white tiger was shot. But these variants have survived in modern menageries.

White tigers are mythical, romantic creatures, which might account for why they’ve been heavily bred in some zoos, notably the Cincinnati Zoo in Ohio, in recent decades. But some have argued that white tigers should be allowed to die out. Here’s what Slate had to say in December:

On the face of it, being a white object in the Bengal tigers’ tropical habitat of India and Southeast Asia can’t be good for a predator that needs to be camouflaged. Other, more subtle problems that go along with the white coat would also prevent white tigers from ever becoming established as a wild population. The mutation (which is not albinism—white tigers can still produce melanin) also causes serious defects. White tigers in captivity tend to have problems with the way that their brains control their eyes and process visual stimulation. The animals are often cross-eyed in one or both eyes, bump into objects, and have trouble understanding spatial relationships when they are young. Animals with defects like these couldn’t survive for long in the wild, even though they have long lives in captivity. Other disorders, such as kidney problems, club feet, and shortened tendons, come from the severe inbreeding required to keep this recessive gene around.

But the new study knocks down several of these arguments. Over the years, the researchers write, many of the white tigers that were captured or killed were mature adults, so lacking the orange-and-black camouflage couldn’t have been too much of a problem. And, inbreeding — not the white mutation itself — accounts for many of the health problems that modern white tigers face, including deformities, stillbirths and premature deaths, they say.

“Despite its low frequency, this polymorphism has persisted for at least several hundred years and should be considered a part of the genetic diversity that is worth conserving,” the scientists argue in their paper.

There’s still a question, however, of whether devoting scarce conservation resources to preserving a rare variant of a creature is worth it when the entire species is threatened with extinction. There may be as few as 3,000 of these cats left in the wild. Their habitat is shrinking. And they’re being devastated by the wildlife trade. With tigers facing threats like those, perhaps a dedicated program to preserving the white mutation is little more than a luxury, even if it could be done more responsibly, with less inbreeding.

After reading the new study, I wouldn’t call white tigers “freaks,” as William Conway, former director of the New York Zoological Association, once did. And I’ll watch in amazement should I encounter one in a zoo. But I won’t be sad if the current (in)breeding programs go away and the money and resources get redirected to other conservation efforts. Because all I want is the tiger, any tiger — white, orange, Siberian, Bengal, Sumatran, et cetera — to continue to survive.

Image credit: Chimelong Safari Park, via EurekAlert

May 23, 2013Permalink Leave a comment

How Might Climate Change Affect Asian Elephants?

elephantsThis morning’s news brought word of a study in Nature Climate Change that predicts devastating global species losses as a result of climate change. The analysis found that some 57 percent of plants and 34 percent of animals would lose more than half of their range by the 2080s if nothing is done to stem the tide of rising greenhouse gases.

“This broader issue of potential range loss in widespread species is a serious concern as even small declines in these species can significantly disrupt ecosystems,” the study’s lead author, Rachel Warren of the University of East Anglia in England, said in a statement.

But it might be easy for many people to ignore something as nebulous as “plants” or “animals” or “ecosystems.” After all, maybe your favorite one won’t be affected. So lets look at another recent study, one of Asian elephants in Myanmar (Burma) that was just published online in Ecology.

Researchers from the United Kingdom and Germany analyzed longevity data from 1,024 semi-captive elephants that were born between 1948 and 1999. These elephants are used in places like the timber industry in Myanmar. They work during the day but forage for food on their own at night, and they breed at will. They have many similarities to fully wild elephants but are easier to study.

This dataset included not just information on how long each elephant lived and how they died, but also about the environmental conditions during their lifespans — specifically, temperatures and rainfall. That let the scientists see how the elephants survived during hot versus cold spells, or during rainy seasons and droughts.

Both temperature and rainfall influenced the survival of elephants over the time of the study. Heat was especially bad — most deaths occurred when temperatures were above 24 degrees Celsius (75 degrees Fahrenheit). Very cold times also weren’t good for the elephants, nor was drought.

That is not good news for Asian elephants, which are already dwindling in numbers. Southeast Asia is expected to warm by up to 3 degrees C over the next 30 to 40 years, accompanied by changes to the yearly monsoon season. “Increased extremes in temperature and rainfall (both within a year and between years) may therefore lead to significant increases in mortality of Myanmar elephants in the near future,” the researchers write.

There has been some debate in the scientific community about whether long-lived creatures will be affected all that much by climate change, and whether species in tropical regions, already adapted for heat, will do as badly under warming conditions. This study, of long-lived elephants living in tropical Myanmar, puts holes in both those theories. “Despite living in a highly seasonal environment, our results indicate that modest deviations from optimal conditions have effects on Asian elephant survival,” the researchers write. Elephant survival under even modest climate changes, therefore, will be a challenge.

Image of elephants in Myanmar courtesy of flickr user Mandala Travel

May 13, 2013Permalink Leave a comment

Not All Animals Make Great Moms, But These Do

I sent my mom a card for today that highlighted how turtles weren’t the best of mothers — they lay their eggs and leave. No turtles are known to care for their young. But there are plenty of animals, including humans, that make great moms. And the Smithsonian’s National Zoo published a bunch of pictures of them on flickr this week. Here are my favorites:

lions

The zoo has two lion moms, Shera and Naba, who in 2010 gave birth to a total of seven cubs. That gave the zoo a full pride of lions. The family has since been split up, but it’s normal for young males to leave and go off on their own. (Photo courtesy of John McRay, Smithsonian’s National Zoo)

elephants

Shanthi gave birth to Kandula in 2001, the first male Asian elephant born in this country that was conceived through artificial insemination. (Although the real reason to include this photo is that my mom loves elephants.) (Photo credit Jessie Cohen, Smithsonian’s National Zoo)

crane

White-naped crane Brenda is serving as a surrogate mom to this little one. The zoo has a captive breeding program for the rare birds in Front Royal, Virginia. (Photo credit: Chris Crowe, Smithsonian’s National Zoo)

gorillas

Gorilla mom Mandara has had six kids over the years. Her youngest, seen here, is Kibbi, born in 2009. (Photo courtesy of Connor Mallon, Smithsonian’s National Zoo)

sealion

Sea lions make great moms, too. Here’s Cali with her two-year-old pup Sophie. (Photo courtesy of Mark Van Bergh, Smithsonian’s National Zoo)

slothbear

Just like a human kid, sloth bear cub Hank tries to upstage mom Hana in this portrait of the two. While Hank is young, though, his mom will carry him on her back most of the time. (Photo courtesy of Connor Mallon, Smithsonian’s National Zoo)

fishingcat

Electra gave birth to two kittens last year, the first fishing cat to do so at the zoo. (Photo courtesy of Janice Sveda, Smithsonian’s National Zoo)

Happy Mother’s Day to all the world’s moms, human and animal!

 

May 12, 2013Permalink Leave a comment

The Marsupial Lion Looked Awesome — Too Bad It’s Extinct

marsupiallion

Here in the United States, we’re familiar with extinct megafauna like mastodons and mammoths, the saber-toothed tiger and the giant sloth. But the list of huge critters that went extinct long ago is sometimes surprising (there’s the saber-toothed salmon, for example), especially when we look outside North America.

In Australia, for example, there’s the marsupial lion (Thylacoleo carnifex), which lived about 1.6 million to 46,000 years ago. Despite its name and a size that was similar to that of a lion, it was not a cat — it’s more closely related to koalas and wombats — but it was the largest meat-eater ever to live on the continent.

That date for when the marsupial lion died out happens to match pretty closely to when humans first arrived on Australia, and that has led many scientists to wonder whether humans drove the species extinct. But a study released this week by the Proceedings of the National Academy of Sciences says no, that species and other megafauna of the region known as Sahul (which includes Australia and New Guinea) were the victims of climate change, not human hunters.

“It is now increasingly clear that the disappearance of the megafauna of Sahul took place over tens, if not hundreds, of millennia under the influence of inexorable, albeit erratic, climatic deterioration,” the study’s lead author, Stephen Wroe of the University of New South Wales, said in a statement.

It’s too bad that the marsupial lion was lost, because it appears that it would have been a pretty awesome animal: It had semi-opposable thumbs, for instance, which may have helped with holding prey. But I probably wouldn’t have wanted to meet one out in the wild.

Artwork by Peter Schouten, via EurekAlert

May 8, 2013Permalink Leave a comment

Bad News For Animals That Live In The Subnivium

voleYou’ve probably never heard of the “subnivium.” That’s because it’s a term that scientists just made up (they do that). The group of ecologists and biologists, led by Jonathan Pauli of the University of Wisconsin, say in an article recently published in Frontiers in Ecology and the Environment that the subnivium is the seasonal refuge that occurs below the snow where there’s environmental stability. It’s cold there, with temperatures near freezing, but this region serves as a retreat from the harsh, sometimes changeable environmental conditions above.

A healthy subnivium contributes to a healthy ecosystem. Insulated soil lets microbes and fungi breathe and proliferate and process organic matter. Plants benefit from increased carbon dioxide and warmer temperatures, especially during late winter and early spring. Many animals — a list that includes invertebrates, amphibians, reptiles, birds, and small mammals — will use the region to hide out during the winter, feeding off each other or any vegetation they can find. There are whole ecosystems below the snow.

But warming conditions have led to many changes in the patterns of snow in the Northern Hemisphere (that’s where most of the world’s snow is found): The month of maximum snow cover has shifted from February to January. The spring melt is about two weeks earlier than it was decades ago. The extent of land covered in snow in the winter has been shrinking. In many places, the amount of time when snow is more likely than rain has decreased by more than one and a half months. Snow depths are decreasing, as are snow packs. The list goes on and on.

“Snow cover is becoming shorter, thinner and less predictable,” Pauli said in a statement. “We’re seeing a trend. The subnivium is in retreat.”

With all these changes, the stability that the subnivium provides is therefore disappearing. What does that mean for the ecosystems that thrive there? One worry is that organisms, such as plants, that are exposed to cycles of freezing and thawing could experience tissue damage. Others, like voles or insects, that lose the layer of snow that hides them may be subject to predation by birds or other critters.

“Decay of the subnivium will affect species differently, but be especially consequential for those that lack the plasticity to cope with the loss of the subnivium or that possess insufficient dispersal power to track the retreating range boundary of the subnivium,” the researchers write. Those that can adapt to the loss of stability or can move to places where there’s still reliable snow cover will do better than others. Adapt or move — those seems to be the only two options for surviving climate change.

Image of vole courtesy of flickr user musubk

May 7, 2013Permalink 2 Comments

You Might Find A Hibernating Lemur Underground

lemur1When I think about hibernation, I picture a squirrel nestled in a tree or a bear in a cave, waiting out the winter. Primates don’t hibernate, and there would especially be no reason for tropical ones to do so, right? But in 2004, scientists discovered a lemur in western Madagascar that did, breaking the no-primate and cold-winter-only rules. The fat-tailed dwarf lemur uses hibernation — the state in which metabolic rates are lower, the animal’s core body temperature matches that of its environment, and certain physiological functions cease — to survive the dry season. The animals hide out in tree holes while temperatures are hot, water dries up, and food disappears, emerging months later when conditions are more friendly.

Now a group of scientists, from the United States, Germany, and Madagascar, report that they have found two more species of lemurs — Sibree’s dwarf lemur and Crossley’s dwarf lemur — that also hibernate. Their study appears in Scientific Reports.

These two species of dwarf lemurs live on the east side of Madagascar, in high-altitude rainforest. This area of the country also experiences wet and dry seasons, but the temperature variations here are greater. It never gets warmer than 85 degrees Fahrenheit and it sometimes reaches temperatures below freezing, making this one of the coldest places in Madagascar.

During the cold winters, the researchers found, the two eastern dwarf lemur species dig burrows into the moist, soft soil and wait out the cold. “Underground shelters provide effective insulation during cold winters, when the ground is frozen or covered by a thick layer of snow,” the researchers write. “In Madagascar’s eastern forests, burrows provide more insulation — i.e., more stable hibernaculum temperature than tree holes or nests.”

That stable environment helps the lemurs keep a more stable body temperature throughout the winter, when ambient air temperatures can fluctuate wildly. The hidey holes might also keep them safer from predators, the researchers hypothesize, particularly if the lemurs are most likely to get eaten when exiting or entering their places of rest.

Unlike the fat-tailed dwarf lemur, these eastern species have a hibernation that looks more familiar, like that of a squirrel or chipmunk. It’s not so surprising, though. The researchers even admit this in their paper. But it can be hard to give up the assumptions we make, especially about things we learn when we’re kids. (And by the way, bear hibernation isn’t as straightforward as you were taught either.)

Image of Non-hibernating Crossley’s dwarf lemur from Tsinjoarivo forest courtesy of K. Dausmann

May 2, 2013Permalink 1 Comment

Lions Are Not Tigers (And Neither Should Be Killed For Their Bones)

lions

Tigers have lost more than 90 percent of their habitat and now number only about 3,200 cats in the wild. One of the biggest threats has been the wildlife trade — every part of the beautiful striped kitties is used in traditional “medicine.”

And now, says the Guardian, there are so few tigers that vendors have switched to lions, which are more numerous (though still vulnerable) and, conveniently, raised by the hundreds for perfectly legal trophy hunting in countries like South Africa:

After the kill [lion breeder Koos] Hermanus will be paid $10,000, but he can boost his earnings further by selling the lion’s bones to a Chinese dealer based in Durban. At $165 a kilo (an average figure obtained from several sources) the breeder will pocket something in the region of $5,000.

If his client does not want to keep the lion’s head as a trophy, the skull will fetch another $1,100. “If you put your money in the bank you get 8% interest,” he explains, “but at present lions show a 30% return.”

Some breeders are reportedly slaughtering their lions, without getting proper permits, just for the bones.

This legal market may be appalling, but it’s only half the trade in lion bones; the rest comes from poaching. Lions are under incredible pressure from the human population in Africa. According to a report last year from Panthera, lions have already lost 75 percent of their habitat, and another report from 2008 found that lion numbers had dropped by more than 75 percent.

A person can sympathize with people in Africa who kill lions because the cats are killing their livestock or, worse, members of the village. But to lose lions to superstitious nonsense is ridiculous. Tigers may be extinct by 2022 — will lions soon follow?

Image courtesy of flickr user Earth-touch Admin

April 24, 2013Permalink Leave a comment

Don’t Bother Trying To Direct An Elephant To Lunch By Pointing

elephant

Asian elephants fall into this odd space between wild and domesticated. They’ve been used as beasts of burden in places like India and Thailand for hundreds of years, but they have never been domesticated. Instead, they are trained, beginning at the age of just two or three, and then put to work for the rest of their lives, sometimes until after they reach age 60.

That odd space got some scientists, led by the University of Cambridge in England, wondering how Asian elephants might respond in something called the “object-choice experiment.” In that test, two containers are placed in front of an animal subject. One of the containers is filled with food, and the other is empty, but the animal can’t tell just from looking at them. Then a human experimenter points or gazes at the container with the food.

Some animals figure out where the food is, but many don’t. Domesticated species — including dogs, cats, horses, and goats — can perform this trick, and so can some wild species. There’s a theory, though, that domestication gives animals an evolutionary heads up in the task, priming them to understand the gaze or actions of humans.

But maybe Asian elephants could also do this, the researchers posited, since they spent so much of their lives around people. And so the scientists tested seven elephants at the Golden Triangle Asian Elephant Foundation in Thailand, setting them up with their personal mahouts (caretakers) as the experimenting human, as seen here in drawing A:

elephant_setup

Drawing B is what’s supposed to happen. Unfortunately, the scientists were wrong, and the elephants proved unable to follow the pointing finger or directed gaze of their mahouts. The pachyderms were successful, though, when they were given verbal instructions meaning things like “left” or “right.”

So what does this mean for the domestication theory? Well, it might be another notch showing that the theory holds true, but perhaps not. As the researchers note in their paper in PLOS ONE, the mahouts use more than verbal cues when directing their elephants. They sometimes point, directing an animal to pick up a tourist’s dropped flip-flop, for example. And so the mahouts were actually upset when their elephants didn’t seem to pick up their non-verbal instructions in the experiment; after all, their animals did something similar every day. Why not then?

Maybe it was just that the experimental setup was an unfamiliar situation, the researchers suggest, and when put in such circumstances, the elephants react better to verbal rather than visual cues.

I’d be curious to see what would happen if the elephants knew the test better, or if the experiment was adapted to be more like what the animals encounter every day. Perhaps then they’d show, in the experimental setting, that they can pick up on the directions from their mahouts as well as they do in their day-to-day lives.

Top elephant image courtesy of flickr user Werner Witte; Diagram of experiment setup from Plotnik JM, Pokorny JJ, Keratimanochaya T, Webb C, Beronja HF, et al. (2013) Visual Cues Given by Humans Are Not Sufficient for Asian Elephants (Elephas maximus) to Find Hidden Food. PLOS ONE 8(4): e61174. doi:10.1371/journal.pone.0061174

April 19, 2013Permalink Leave a comment

Why Climate Change Could Be Bad News For Snowshoe Hares (And Lynx)

hareThe snowshoe hare (Lepus americanus) has mastered the art of camouflage. In warm times, its coat is a muddled brown, easily blending into a background of trees, rocks, and dirt. As the days shorten and the temperatures begin to drop, it sheds its coat and grows a new one of snowy white, perfect for the snowy days sure to follow.

There’s been worry, however, that this well-honed system could fall apart under climate change: If winters get shorter and snowshoe hares don’t change the timing of their molts, they could be left vulnerable to predators, bright white targets on a brown background.

That worry may be well founded, according to a study published today by PNAS. Researchers from the University of Montana in Missoula and the University of Idaho in Moscow found that the timing of molts, both fall and spring, is tied to the length of day, and the snowshoe hares have no ability to change their fall molt and only a little for the spring.

They draw that conclusion from studying 148 snowshoe hares in the wild over three consecutive Montana winters from 2010 to 2012. Those winters were significant because they were very different and included one that was particularly long and another that was very short. That allowed the scientists to see if the hares adapted to changes in winter length.

The molt from brown to white in the fall was fixed, starting at the same time every year and taking 40 days to complete. In spring, there was a little change in 2011, the year of the really long winter, and the hares completed their transition back to brown 16 days later than in the other two years.

But when the researchers extrapolated from these three years to what may happen later this century, as temperatures rise and winters get shorter, they found that the number of days that snow-white hares can be found in brown landscapes would increase by fourfold by the middle of the century and eightfold by its end.

That’s definitely bad news for snowshoe hares, but it may also bode ill for the Canada lynx (Lynx canadensis, not named particularly well since it’s also found in the United States). The ecology of lynx and snowshoe hares is intertwined, as Smithsonian reported a couple years ago:

The northern [Canada and Alaska] lynx population rises and falls according to the snowshoe hare’s boom-and-bust cycle. The hare population grows dramatically when there is plenty of vegetation, then crashes as the food thins out and predators (goshawks, bears, fox, coyotes and other animals besides lynx) become superabundant. The cycle repeats every ten years or so. The other predators can move on to different prey, but of course the lynx, the naturalist Ernest Thompson Seton wrote in 1911, “lives on Rabbits, follows the Rabbits, thinks Rabbits, tastes like Rabbits, increases with them, and on their failure dies of starvation in the unrabbited woods.” Science has borne him out. One study in a remote area of Canada showed that during the peak of the hare cycle, there were 30 lynx per every 40 square miles; at the low point, just three lynx survived.

The boom-and-bust cycle of hares and lynx isn’t quite as dramatic in the animals’ southern range, where forests are patchier and lynx less common. But all lynx are snowshoe hare specialists, and that specialization may put them at risk. If the hares become more vulnerable to climate change, that doesn’t mean that lynx will automatically get more of them. Other predators (the goshawks, bears, fox, coyotes, and other animals mentioned above) could get to them first, leaving fewer for the lynx. And the lynx, because they’re specialists, won’t be able to fill their tummies with anything else, resulting in, ultimately, fewer lynx.

There are at least nine other mammal species that undergo coat changes in winter similar to that of the snowshoe hare, and unless they’re able to adapt their timing, they will face scenarios also similar to the snowshoe hare. The forces of evolution may help out some of these species, though — as the researchers note in PNAS, natural selection should not be discounted.

Image courtesy of flickr user DenaliNPS

April 15, 2013Permalink Leave a comment