Category Archives: Animals

Effects of climate change on polar bears

Polar bears (Ursus maritimus) are in the news again because of dire predictions for the coming decades on their population numbers. The effects of climate change have been predicted to impact the polar regions first and most dramatically according to most models, and indeed, it is at the poles where we are recording some of the most dramatic examples of climate change. Polar bears, being the largest of the living bear species, are charismatic and popular, and because of the likely impact that climate change will have on them they have become a poster species for the climate issue.

Polar bear, Ursus maritimus.

In a recent interview bear expert Andrew Derocher predicted that one population of polar bears (western Hudson Bay) could see its numbers drop too low to be viable within three decades (Yale Environment 360 2010). We have explored polar bears and their populations in other posts. Here I want to examine why changes in sea ice and warmer periods are such a concern for polar bears.

Polar bears evolved relatively recently, diverging from an ancestral brown bear population about 150,000 years ago (Lindqvist et al. 2010). There is a unique population of brown bears that live on Admiralty, Baranof, and Chichagof (ABC) islands of southeastern Alaska’s Alexander Archipelago. This population, called the ABC bears, is the closest brown bear relatives of the polar bears—early members of this population split off to live full time on the sea ice, evolving into the modern polar bear species. Thus, polar bears are an example of rapid mammalian evolution, undergoing morphologic changes such as elongated snouts, overall size changes, furry padded feet, and color changes, as well as social and metabolic changes to adapt to the rhythms of the arctic seasons.

It is their complex adaptations to living on the rugged ice that makes them most susceptible to changes in that habitat. They use the ice as a platform for hunting seals, as a habitat for finding mates and mating, and for traveling long distances. As the ice breaks up earlier in the spring, and re-freezes later in the winter, several weeks of prime hunting time are taken away from the polar bears. Today, they are able to spend almost three weeks less on the ice hunting than they were able to several decades ago. This is critical because after the ice breaks up for the year, the bears must fast until the next season, and longer times of open water means long fasting periods.

This can be critical for a female bear that must gestate her young, birth them, and begin to nurse them to a size large enough that they can accompany her onto the ice for hunting the next season. So, she is expending a great deal of energy in contributing to the growth of her young while fasting. If she did not build enough fat reserves the year before to withstand this metabolic marathon, she and her offspring will not survive into the following year. A few additional weeks of having to fast can be the difference between life and death.

The intimate connection that polar bears have evolved with their arctic habitat means that they are finely tuned to changes in that world. And with the effects of climate change appearing in the arctic regions first, they are in fact akin to the “canary in the coal mine,” a harbinger of things to come.

References:

Lindqvist, C., S. C. Schuster, Y. Sun, S. L. Talbot, J. Qi, A. Ratan, L. P. Tomsho, L. Kasson, E. Zeyl, J. Aars, W. Miller, Ó. Ingólfsson, L. Bachmann, and Ø. Wiig. 2010. Complete mitochondrial genome of a Pleistocene jawbone unveils the origin of polar bear. Proceeding of the National Academy of Sciences.

Yale Environment 360. 2010. For Hudson Bay polar bears, the end is already in sight. http://e360.yale.edu/content/feature.msp?id=2293.

Mountain Lions

They go by many names: puma, mountain lion, mountain cat, catamount, and panther, and scientifically as Puma concolor. The mountain lion is presently North America’s second largest cat, with the jaguar (Panthera onca) being the largest.

Mountain lions are widely distributed, from the Yukon Territory in Canada south through the western states, through Mexico and to the tip of South America, giving it one of the widest distributions of any species in the New World. There is a second population center in Florida, a relic population from when the species was spread coast to coast during the Ice Age. Recently, there is evidence that they are pushing their way onto the Great Plains states from the west, with reports of sightings as far east as Kansas.

They are large predators, with males weighing approximately 140 pounds, and females 90. They are considered the largest of the small cats. What?

Cats have been divided into two subfamilies, with the big cats being tigers, lions, leopards, and jaguars. The small cat subfamily includes the smaller cats like lynx and a host of species like jungle and mountain cats, marbled cat, and ocelot. The small cats also include your house cat.

Like all cats, the mountain lion is carnivorous and eats meat exclusively. They will eat anything they can catch, from insects to large animals like deer, and very occasionally elk and moose. They also are known to kill domestic livestock including cattle, horses, and sheep. It is this that caused the cats to almost be exterminated, but with legal protection their numbers are making a comeback.

The mountain lion, Puma concolor. Photograph by Bas Lammers.

This post is another in the dangerous animals series where we are exploring animals of North America that could be considered a threat to humans. However, like all the other animals, the threat is very small. Mountain lions have been known to attack and kill people, but it is a rare occurrence. Humans are increasingly moving into remote areas that host mountain lions, and encounters are increasingly likely, but mostly encounters involve seeing the tail-end of the cat disappearing.

Attacks are rare because unless they are threatened or cornered, attacks are brought about as the cat is hunting for prey, and since they are not habituated to seeing humans as prey, they avoid people. Many who are attacked are smaller in stature, such as children or women, and victims are often jogging or engaged in a similar activity that might trigger the pursuit instinct in the cat when they are very hungry.

Mountain lion foot print at a dinosaur dig in Colorado.

It is for this reason that it is recommended that if you encounter a mountain lion you should make yourself look less like prey and more like a handful. Standing up large, waving your arms, shouting, and such things will discourage the cat from attacking. Do not run.

Between 1890 and 2005 there were 88 attacks on people, and 20 fatalities (Arizona Game and Fish 2010), so on average there are a few attacks, and fewer than a single death, each year. As far as risks that we live with everyday this is really is not much of a danger.

Average number of deaths per year caused by various animals

I have been fortunate to have seen a glimpse of one of these great beasts in the wild, and if you are so lucky, cherish the moment.

Arizona Game and Fish. 2010. Confirmed mountain lion attacks in the United States and Canada 1890 – present. http://www.azgfd.gov/w_c/mtn_lion_attacks.shtml.

Shark bites in the Cretaceous Sea

One of the most exciting things in paleontology is being able to definitively establish the interaction of two species from the fossil record. It is thrilling to picture a moment in time, millions of years ago, when two animals were at the same place, at the same time, and be able from fossil evidence to glean something about their interaction and behavior.

One dramatic example of this is finding a fossil with clear evidence that it was bitten by a shark. During the Late Cretaceous, North America was cut in half by an interior sea that extended the Gulf of Mexico across the mid-continent to connect with the Arctic Ocean in the north, effectively creating two land masses where today there is one.

In this last period from the Age of Dinosaurs, fantastic and strange creatures swam the seas. Today, the sediments from that ocean are exposed in badlands across much of western Kansas, Nebraska, and South Dakota. These geologic formations, like the Niobrara Formation, preserve a rich record of the ocean life, and clearly show what a scary ocean it was.

Tylosaurus model from the Carnegie Collection

Giant marine lizards thrived in the sea. These beasts, close relatives of modern snakes and lizards, were called mosasaurs. There were several kinds that likely had different modes of life, some making use of resources close to the surface, and other species specializing in deep-water feeding, with the largest of them reaching 50 feet in length. They were joined by another group of marine reptiles called plesiosaurs. Plesiosaurs occur in two basic body plans, with the unimaginative names of long-necked and short-necked for obvious reasons.

Long-necked plesiosaur Styxosaurus

The long-necked plesiosaurs have been described as looking like a turtle with a snake threaded through its shell. They had a stocky, turtle-like body, enormously long necks capped by a remarkably small head, and stumpy tails. They had four large flippers that helped to propel them through the water as well.

Short-necked plesiosaurs had large heads attached to short, thick necks. The long-necked forms most likely specialized in eating smaller fish with their small heads, maybe using their long necks to “snake” their way amongst their prey before being noticed. The short-necked forms obviously ate large prey, as evidenced by their massive heads and powerful jaws. (You can find models of both long and short-necked forms, as well as mosasaurs as part of the collection of dinosaur toys).

Living alongside these giants of the sea were animals that we would easily recognize, at least for their general body plan—these were the sharks. There was a significant amount of shark diversity in the Interior Sea as well, from relatively small forms that likely ate near the sea floor, to mid-sized forms that ate smaller fish and scavenged on dead carcasses, to several very large species that rivaled the modern great white shark in size and ferocity.

On occasion, when finding remains of fish or the marine reptiles, we find evidence of those remains having been bitten by sharks. The most compelling evidence is when teeth are found embedded in the fossil remains, but also punctures and tooth scratches can be a telltale sign.

Several plesiosaurs have been found as partial skeletons, with bites in several areas of their body, suggesting that after they died and settled to the ocean floor their carcass was scavenged by mid-sized sharks.

Cretoxyrhina bites the back of a mosasaur in the Late Cretaceous. Painting by Dan Varner.

And in one dramatic example, the great white of the Kansas seas bite the back of a mosasaurs, cutting a section of vertebrae completely out of the giant lizard. The section of back, with its included vertebrae, was later spit out by the shark after having been mostly digested. The gristly remains settled to the ocean floor to lie there for millions of years before being found and placed in a museum.

Today we are fascinated by tales of shark attack, with the movie Jaws being a prime example. You can learn about these dangerous animals in another post, but perhaps it gives you some comfort to know that the denizens of the ancient seas also were subject to shark bites!

Additional information about this specimen can be found at Oceans of Kansas.

Venomous Snakes of North America

This is the latest post in the Dangerous Animals series. Snakes cause some people to have a physical reaction of fear and revulsion, which is too bad as they are fascinating creatures. In many years as an educator about the natural world, I loved to use live snakes as examples. Many species can be safely handled and brought out with the public. They always create a stir among the viewers, some right up front with wide-eyed excitement, and others trying to appear casual while they move to the back of the crowd to let others get a good view.

I always respected the feelings of those folks who felt a bit uncomfortable, and ironically it was often the big, burly, macho males of the group for whatever reason. Numerous times in such situations I watched as the boy in class with great fear at first watched others touch the snake, with comments like “Oh, it is not slimy,” or “Wow, it feels cool,” and then slowly make his way to the front. It was always a great personal triumph when he screwed up his courage enough to tentatively reach out a finger to touch the snake and overcome some of his own demons.

As an aside, it also always upset me when I would see one spouse, usually the man, use one of the very realistic snake models we had to sneak up on his wife and scare her with it. That is not helping at all.

I think such fear is caused by a lack of understanding about these amazing creatures, and the knowledge that some of them are dangerous animals. That combination leads to lots of misinformation and confusion. The vast majority of snakes are harmless to humans, and all of them serve an important role in their ecosystems, being predators on small species helping to keep their numbers in check.

The venomous snakes of North America fall into two families: the vipers and the elapids. The vipers, more specifically pit vipers, include the copperhead (Agkistrodon contortrix), the cottonmouth (Agkistrodon piscivorus), and the rattlesnakes (about 30 species in the genera Crotalus and Sistrurus). The pit is a special heat-sensing organ located on either side of the head, between the eye and nostril, which allows the animal to track changes in temperature in its environment. This is most useful for tracking warm-blooded prey such as small rats at night, without needing light. In experiments, the snakes can be deprived of vision and a sense of small, and still stalk prey and strike with great accuracy.

Eastern Coral Snake

The second group of venomous snakes belongs to the family Elapidae, the family that includes many deadly snakes such as cobras, sea snakes, and kraits. The coral snakes (Micrurus and Micruroides) are the New World representatives of this family. They live in three areas across the south. The eastern coral snakes lives in the Carolinas south to Florida. The Texas coral snake lives in Texas and Louisiana, and the Arizona coral snake lives in Arizona and extreme southern New Mexico. They are reclusive snakes, mostly living underground, are nonaggressive, and account for very few snakebites each year, which is a good thing because their venom is a very potent neurotoxin. Read more about venom here.

The copperhead is one of the most beautiful snakes in my opinion. They live in the eastern woodlands of North America, being found from Kansas and Oklahoma east through the southern and New England states.

A copperhead snake, Agkistrodon contortrix, perhaps one of the most beautiful snakes in North America.

It can be found in northern Mexico in desert areas, but is closely associated with semipermanent water sources and riparian areas. It is a docile snake, and mostly relies on its coloration to keep it hidden. I have known hikers to step right over the snake without ever seeing it or having the snake react, which can also lead to bites when it gets stepped on directly. The venom of the copperhead is less toxic than the other pit vipers, and bites are generally less severe than from other venomous snakes.

There is a great deal of worry about the cottonmouth in the area that I grew up in, Ohio, which is ironic since they do not occur there. (I have observed this phenomenon over and over, with people being deathly afraid of species, having heard from so and so some horrific story about it, and just sure that they are of great concern when it does not even occur in the area. Humph.) They do occur across the southeast states, from extreme southern Virginia through Florida, and west to Oklahoma and central Texas.

Cottonmouth

The cottonmouth is closely related to the copperhead, but its temperament is not as docile. One of the reasons that this snake causes fear I think is because it can be hard to identify in the field if you are already predisposed to fear snakes. It is a heavy-bodied snake that is generally dark olive in color and resembles several species of harmless water snake. When threatened, the snake may open its mouth wide, flashing the white interior of its mouth as a warning, giving it the name cottonmouth. Its resemblance with several species of harmless snakes gives rise to far more “encounters” with cottonmouths being reported than actually occurs.

The rattlesnakes are a diverse group of snakes that only occur in the New World, and a species of rattlesnake occurs in every state in the contiguous United States expect for Maine. They do not live in Alaska or Hawaii. The largest native snake in North America is the eastern diamondback, which can reach over 7 feet long, although that is rare. (The indigo snake can be longer, but the eastern diamondback is heavier bodied.)

Timber Rattlesnake

Their most obvious physical trait of rattlesnakes is the presence of the rattle, which is a modified string of scales on the end of the tail. The scales interlock in such a way as to allow the snake to shake its tail vigorously and cause the scales to rattle, giving notice to animals around it that it is there. As a warning system, it likely evolved so the snake could let large ungulates, that move in big herds, know that the snake was there specifically to avoid being stepped on. The snake most definitely would like to be left alone so it does NOT have to bite to defend itself. Listen to a rattlesnake here

Rattlesnakes would mostly like to avoid confrontations with humans too. When disturbed it will make its presence known and try to make a retreat. Some species are more likely than others to stand their ground and not flee. Bites most often occur when people fail to leave the snake alone, or surprise the snake unexpectedly, such as reaching under a log or into a rock crevice.

Venomous snakes do cause just over 5 deaths per year in North America (Langley 2005), and more bites that do not cause death, but injury and pain. (See this post for information about the number of bites each year). However, that number of fatalities and injuries caused by snakes pale in comparison with automobile deaths nationwide, with over 37,000 occurring in 2008. But automobiles are part of our everyday experience, which engenders a more blasé attitude generally than snake encounters.

Average number of deaths per year caused by various animals

Advice for outdoor adventures in areas where venomous snakes occur is pretty basic. Use common sense, be careful when around rocks and logs where you cannot see underneath, do not provoke any snakes encountered, and give the snake plenty of room to retreat. If a bite does occur, don’t panic and seek medical treatment right away. While a bite is a medical emergency, the modern antivenin available is very effective at mitigating snake venom

Langley, R. L. 2005. Animal-related fatalities in the United States–an update. Wilderness & Environmental Medicine 16:67-74.

Venom, Poison, and Toxicity

There is a great deal of confusion about the terms venom, poison, and toxicity, and they are often used in an imprecise manner. However, the subject is great fun, so let’s explore it a bit.

First, we should clear up the difference between venom and poison. Venom is a substance that is generally injected, such as through a bite. Poison is something that is ingested, such as by eating or inhaling. So, these words relate to how the substance is gotten from point A to point B. Therefore, it is not correct to describe a snake as poisonous, unless it caused you some reaction if you ate it (beyond the thought of eating a snake, that is).

Dance Macabre

Monarch Butterflies, on the other hand, are poisonous. They take up toxic substances from the food source of the caterpillars, the milkweed plants, and by concentrating the toxins in their body, they become poisonous to consume. This is a defensive mechanism, not so much for the individual, but for the species as a whole. Any single individual might get eaten, but the effect on the eater is hoped to be so unpleasant as to cause it to not want to eat another one, so the entire species benefits.

Toxicity refers more to the effects of poison or venom. It is a descriptive term used to characterize the medical impact. So, venom can be more or less toxic and still be venom. All spiders are venomous (that is, they inject a venom), but not all spiders are equally toxic, and therefore dangerous, to people.

And, not to put too fine an edge on it, there are things that are toxic without being venom or poison. If you save up a bunch of your saliva, and then loaded it into a syringe and injected it into your skin, you would find that it has a toxic effect on the injection site. That is, the proteins in the saliva would begin to act upon the proteins in your tissues, but we hardly consider humans venomous.

Venom is found throughout the animal kingdom and serves a wide variety of purposes. Some of the most dangerous animals are venomous. Venom can help secure food, as in wasps that sting their victims to lay eggs upon for feeding the larva, or in shrews that bite their prey and inject venom to help immobilize it. Spiders, too, inject venom, which helps immobilize and kill they prey, but it also begins the digestive process so the spider can feed upon the liquefied remains.

Venom can be defensive. For example, a colony of honey bees does not need venom to feed, but uses it as a deterrent to would-be intruders on the hive. Fish, such as the lionfish, have spines with venom that can be injected into attackers upon being bitten. And the male duckbilled platypus has a spin on its hind legs that can inject venom, used again rival males in courtship combat.

Snakes are some of the best known, and most misunderstood, of the venomous animals, and snake venom is diverse in its function and toxicity. In general, snake venom falls into two broad categories: hemotoxic and neurotoxic, but in reality, most snakes have components of both.

Hemotoxic means that the components in the venom attack tissues, like in the spider example, such that the venom is breaking down the tissues of the victim in a pre-digestion process. Such venom can cause extensive damage to tissues, great pain, and cause death slowly over a period of time.

Neurotoxic venoms act upon the nerves system, disrupting the ability of the nerves to send and receive messages. The effect of this kind of venom is that critical nervous system signals stop, such as the signal to your lungs to breath, or to your heart to beat. This kind of venom can act very quickly to cause death.

The vipers, the rattlesnakes, copperheads, cottonmouth in North America, have venom that is mostly hemotoxic, with lesser amount of neurotoxic components. The elapids, the coral snake in North America, and its relatives like the cobras, have venom that is mostly neurotoxic.

So now you can be erudite at parties when friends say things like “Watch out, that black widow you are about to sit on it poisonous!” You can smile politely as you sit, and say “Actually, it is venomous. Let me tell you all about it.”

Boneblogger: Science and the outdoors

Exploring the natural world