Monthly Archives: November 2023

Episode 356: The Volcano Rabbit

Posted on by

Podcast: Play in new window | Download (Duration: 6:41 — 7.9MB)

Subscribe: RSS | More

Thanks to Eva for suggesting the adorable volcano rabbit this week!

Further watching:

American Pikas Calling Out

The volcano rabbit is not a volcano but it is a very small rabbit:

The volcano rabbit is SO CUTE:

The American pika looks kind of like its rabbit cousin [photo by Justin Johnsen, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=91574]:

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

This week we have a suggestion from Eva, who wanted to learn about volcano rabbits! What are volcano rabbits? Do they shoot lava at their enemies? Let’s find out! (No, they don’t shoot lava. Sorry. That’d be awesome!)

The most important thing to know about the volcano rabbit is how small it is. It’s almost the smallest rabbit known. It typically only grows about 9 inches long, or 23 cm, and that’s when it’s stretched out. Rabbits usually sit more bunched up, which makes it look even smaller. Its ears are small and rounded, its tail is short even for a rabbit, and its legs are short. Its fur is also short and very thick, mostly grayish-tan in color.

The second most important thing to know about the volcano rabbit is how rare and endangered it is. That’s because it only lives in one small part of Mexico, specifically on the upper slopes of four volcanoes. Because people also live in this area, which isn’t far from Mexico City, the rabbits’ natural range is fragmented by human-made obstacles like highways that are dangerous for it to cross, along with habitat destruction from logging, livestock grazing, and the building of new houses. People even hunt the rabbit even though it’s a protected animal. We don’t know for sure how many of the volcano rabbits are left in the wild, but the best estimate is around 1,200 rabbits in small populations that are often widely separated. It’s even been declared extinct on another volcano where it used to live, although there may be a small population still hanging on.

The volcano rabbit prefers open woodland in higher elevations where there’s plenty of tall, dense grass native to the area. It makes rabbit-sized tunnels through the grass so it can move around undetected by predators. It also mostly eats this grass. It’s most active at dawn and dusk, which also helps it hide from predators.

When a volcano rabbit does feel threatened, it doesn’t thump its feet to alert other rabbits of danger. Instead, it gives a little alarm squeal. This is really unusual in a rabbit, but it’s something the pika does, and the pika is closely related to rabbits. The pika lives in parts of central Asia and western North America, especially in cold areas like mountaintops. It’s so well adapted to the cold that it can die if the temperature climbs over about 78 degrees Fahrenheit, or 25 Celsius.

The American pika actually looks a lot like the volcano rabbit in some ways, although it’s less rabbit-like in shape and more rodent-like, although it’s not a rodent. It’s a lagomorph. It’s about the same size or a little smaller than the volcano rabbit, with short legs and dense grayish-brown fur that grows longer in winter. It especially likes places with a lot of rocks, since it makes its home in little cracks and crevices between rocks. It prepares for winter by harvesting the plants it eats and storing them in little haypiles. Since it doesn’t hibernate, it needs plenty of food for times when snow and ice make it hard to find plants.

The pika is intensely territorial, because it doesn’t want any other pikas sneaking around eating up its hay, but it does communicate with other pikas. During breeding season the males will make a singing call to attract a female, and all pikas will call to warn others of a predator nearby. I couldn’t find any recordings of a volcano rabbit, but this is what an American pika sounds like:

(wait for it…)

[pika beeping]

Like other rabbits, the volcano rabbit eats grass and other plant parts. The problem is that most of the plants in its habitat are not very high in protein. The more fragmented its habitat is, the harder it is for the rabbits to find enough food to survive, much less to also reproduce. Every time someone decides to let cattle or other livestock graze on the local plants, the rabbits have that much less food.

Fortunately, conservationists in Mexico are working on educating people so they know this cute little rabbit is a protected species. Captive breeding programs are underway too, and parts of the volcanoes where the rabbit lives are within the bounds of a national park. There are plans to create safe corridors to link the rabbit’s fragmented habitats so it can come and go without getting squished by cars, and to restore its range with more native plants so it has plenty of food.

You might worry that the volcano rabbit, besides having all these issues with habitat loss and habitat fragmentation, is also in danger of its volcano home erupting. The volcanoes where it lives are active, but only one of the four poses any danger, and that volcano has erupted repeatedly in the last several hundred years without affecting the volcano rabbit. It actually even had a small eruption in May 2023. Schools in the area were closed for a few days, but no one was hurt, not even a rabbit.

You can find Strange Animals Podcast at strangeanimalspodcast.blubrry.net. That’s blueberry without any E’s. If you have questions, comments, or suggestions for future episodes, email us at strangeanimalspodcast@gmail.com. We also have a Patreon at patreon.com/strangeanimalspodcast if you’d like to support us for as little as one dollar a month and get monthly bonus episodes.

Thanks for listening!

Episode 355: Tiny Owls

Posted on by

Podcast: Play in new window | Download (Duration: 9:06 — 10.8MB)

Subscribe: RSS | More

This week we learn about two tiny owls! Thanks to Elizabeth and Alexandra for their suggestions!

Further reading:

Burrowing Owl

Elf Owl

The burrowing owl is tiny but fierce [photo by Christopher Lindsey, taken from page linked above]:

The elf owl is also tiny but fierce [photo by Matthew Grube, taken from page linked above]:

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

This week we’re going to learn about two tiny owls. Thanks to Elizabeth and Alexandra for their owl suggestions!

The burrowing owl is native to the Americas, especially the western part of North America, and most of Central and South America. It prefers grasslands and other open areas. It’s a small owl, not much bigger than the average songbird. It’s mostly brown with lighter underparts that are barred with a brown pattern.

You can tell a lot about an owl by the color of its eyes. In general, an owl with dark eyes is most active at night, an owl with orange or red eyes is likely to be most active at dawn and dusk, and an owl with yellow eyes is often active in the day. That’s not a hard and fast rule, but it can help you make a good guess about an owl’s behavior. The burrowing owl has yellow eyes, and it is indeed active in the day. The term for daytime activity is diurnal.

In past episodes I’ve said that owls have long legs that are usually hidden by feathers. In the case of the burrowing owl, its long legs are in plain sight because it spends a lot of the time running around on the ground. It will sometimes chase prey on foot, but other times it will perch on a fence post, tree branch, or some other high place to watch for a small animal to pass by. Then it will swoop down to grab it just like any other owl. It eats mice and other small rodents, lizards, small snakes, frogs, large insects and other invertebrates like scorpions and caterpillars, and birds. It especially likes termites and grasshoppers. Females are more likely to hunt during the daytime, while males are more likely to hunt at night or at dawn and dusk. Sometimes the burrowing owl will eat fruit and seeds too. When the burrowing owl has more food than it can eat, it will store some in underground larders.

The burrowing owl gets its name because it builds a nest in a burrow in the ground, often in burrows dug by other animals like prairie dogs and skunks. Some subspecies of burrowing owl will dig its own burrow, and all subspecies will enlarge an existing burrow until it’s happy with the size. It uses its beak to dig and kicks the dirt out with its feet. Both the male and female will work on the burrow together. Once it’s the right size and shape, the owl will bring in dried grass and other materials to line the burrow. One of its favorite materials is dried animal dung, especially from cattle. The dung releases moisture inside the burrow, making it more comfortable, and attracts insects that the owls eat. Win-win! It will also scatter animal dung around the entrance of its burrow and will sometimes also collect trash like bottle caps and pieces of foil to decorate the entrance.

The female lays her eggs in the burrow and spends most of her time incubating the eggs, only going outside briefly to stretch her legs. The male stands guard at the entrance to the burrow or nearby except when he’s out hunting. He brings food back for the female.

When the eggs hatch, both parents take care of the babies. At first the chicks stay in the burrow, but as they grow older they come out to play outside and start learning how to fly. Since burrowing owls usually nest in small colonies, there’s always an adult watching for danger somewhere nearby.

Most birds abandon their nests after their chicks are grown. The burrowing owl often uses its burrow year-round, although populations that migrate will usually make a new burrow when they return to their summer range. The burrow gives the owls a place to nap during the hottest part of the day, and it’s also a good place to hide if a predator approaches. Rattlesnakes also use burrows for the same purposes, and when a burrowing owl runs from a predator and hides in its burrow, it will mimic the rattling and hissing of an angry rattlesnake. A lot of times that’s enough to make a predator think twice about digging up the burrow.

This is what a burrowing owl sounds like when it’s not imitating an angry rattlesnake:

[burrowing owl call]

The burrowing owl is increasingly threatened by habitat loss and introduced predators likes cats and dogs. Luckily it’s an adaptive bird and is happy to use artificial burrows in protected areas. It’s a useful bird to have around since it eats a lot of insects, prairie dogs, and other animals that are considered pests by humans. Plus it’s an incredibly cute bird. I mean, it’s a tiny owl with long legs! How could you not find that cute?

Small as it is, the burrowing owl isn’t the smallest owl known. The elf owl is even smaller, about the size of a sparrow. It’s only about 5 inches tall, or 13 cm, with a wingspan of only 9 inches, or 22 cm. It lives in parts of the southwestern United States during the summer and parts of Mexico during the winter.

The elf owl is nocturnal like most other owls, and this is where our guideline of owl eye color breaks down, because the elf owl has yellow eyes. Its feathers are mostly gray or grayish-brown with white streaks. When it’s sitting on a twig, it kind of looks like a dead leaf or a broken-off branch.

It mostly eats insects, but it also likes scorpions, spiders, and centipedes. Occasionally it eats small reptiles or mammals. When it catches a scorpion, it removes the stinger before eating the scorpion, but it doesn’t seem to be hurt by actually being stung. It’s a fast, acrobatic flyer and catches insects on the wing, but it also hunts for insects on the ground and has long legs like the burrowing owl.

The elf owl nests in holes made by woodpeckers in trees or cacti, and the male brings the female food while she keeps the eggs warm. After the babies hatch, the male brings them food too and also continues to feed the female for another couple of weeks, until she starts to hunt again. The male will also catch a tiny snake called the western threadsnake, which looks a lot like an earthworm and only grows a foot long at most, or 30 cm, and is usually much smaller than that. It lives underground most of the time and while it has eyes, they don’t work except to sense light and dark. It eats insects, especially termites and ants. When an elf owl catches one of these little snakes, it doesn’t eat it. Instead, it brings the snake back to the nest and lets it go. The snake eats all the insects it can find, including parasites that might hurt the baby owls. Then again, sometimes the nest is inhabited by tree ants that do the same thing, cleaning up all the parasites and scraps of leftover food while not bothering the owls.

If a predator grabs an elf owl, or a scientist nets and handles one, the owl pretends to be dead. A lot of times this will cause the predator to relax its jaw muscles, which often allows the owl to wiggle free and fly away. The scientists are a little more careful about relaxing their hands, but when a scientist handles an elf owl, it’s usually to do a quick examination and maybe put a leg band on for identification purposes, and then they let the owl go again anyway.

This is what an elf owl sounds like:

[elf owl call]

You can find Strange Animals Podcast at strangeanimalspodcast.blubrry.net. That’s blueberry without any E’s. If you have questions, comments, or suggestions for future episodes, email us at strangeanimalspodcast@gmail.com. We also have a Patreon at patreon.com/strangeanimalspodcast if you’d like to support us for as little as one dollar a month and get monthly bonus episodes.

Thanks for listening!

Episode 354: Sheep and Sivatherium

Posted on by

Podcast: Play in new window | Download (Duration: 10:52 — 12.2MB)

Subscribe: RSS | More

Thanks to Hannah, who suggested sheep as this week’s topic! We’ll also learn about a few other hoofed animals, including the weird giraffe relative, sivatherium.

Further reading:

The American Jacob Sheep Breeders’ Association

What happened with that Sumerian ‘sivathere’ figurine after Colbert’s paper of 1936? Well, a lot.

A Jacob sheep ewe with four horns (pic from JSBA site linked above):

The male four-horned antelope [photo by K. Sharma at this site]:

A modern reconstruction of sivatherium that looks a lot like a giraffe [By Hiuppo – Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=2872962]:

The rein ring in question (on the left) that might be a siveratherium but might just be a deer:

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

This week we’re going to look at an animal suggested by Hannah a long time ago. Hannah suggested we talk about sheep, and I can’t even tell you how many times I almost did this episode but decided to push it back just a little longer. Finally, though, we have the sheep episode we’ve all been waiting for! We’re also going to learn about a strange animal called sivatherium and a mystery surrounding when it went extinct.

The sheep has cloven hooves and is a ruminant related to goats and cattle. It mostly eats grass, and it chews its cud to further break down the plants it eats. It’s one of the oldest domesticated animals in the world, with some experts estimating that it was first domesticated over 13,000 years ago. Mammoths still roamed the earth then. Sheep are especially useful to humans because not only can you eat them, they produce wool.

Wool has incredible insulating properties, as you’ll know if you’ve ever worn a wool sweater in the snow. Even if it gets wet, you stay nice and warm. Even better, you don’t have to kill the sheep to get the wool. The sheep just gets a haircut every year to cut its wool short. Wild sheep don’t grow a lot of wool, though. They mostly have hair like goats. Humans didn’t start selecting for domestic sheep that produced wool until around 8,000 years ago.

Like other animals that were domesticated a very long time ago, including dogs and horses, we’re not sure what the direct ancestor of the domestic sheep is. It seems to be most closely related to the mouflon, which is native to parts of the middle east. The mouflon is reddish-brown with darker and lighter markings and it looks a lot like a goat. Other species of wild sheep live in various parts of the world but aren’t as closely related to the domestic sheep. The bighorn and Dall sheep of western North America are closely related to the snow sheep of eastern Asia and Siberia. The ancestors of all three species spread from eastern Asia into North America during the Pleistocene when sea levels were low and Asia and North America were connected by the land bridge Beringia.

The male sheep is called a ram and grows horns that curl in a spiral pattern, while the female sheep is called a ewe. Some ewes have small horns, some don’t. This is the case for both wild and domestic sheep. Sheep use their horns as defensive weapons, butting potential predators who get too close, and they also butt each other. Rams in particular fight each other to establish dominance, although ewes do too.

But some breeds of domestic sheep are what is called polycerate, which means multi-horned. That means a sheep may have more than two horns, typically up to six. Many years ago I kept a few Jacob sheep, which are a polycerate breed, and in a Patreon episode from 2018 I went into really too much detail about this particular breed of sheep. I will cut that short here.

The Jacob is a hardy, small sheep with tough hooves, and it’s white with black spots. Ideally, a Jacob sheep will have four or six well-balanced horns. In a six-horned sheep, the upper pair branch upward, the middle pair curl like an ordinary ram’s horns, and the lower pair branch downwards. Sometimes a sheep will have three or five horns, or will start out with four horns but as they grow, two will merge so it looks like they have a single horn on one side. Sometimes a ram’s horns will grow so large that the blood supply is choked off for the lower pair, which will die and stop growing. Breeding a pair of six-horned Jacob sheep doesn’t guarantee that the babies will have more than two horns, though. It’s still a recessive trait.

Sheep, goats, cattle, and some antelopes are all bovids. Polyceratism appears to be a bovid trait. It’s caused by a mutation where the horn core divides during the animal’s development.

Occasionally, a sheep of non-polycerate breed, or a goat, or even a cow, is born with multiple horns. The blue wildebeest is also occasionally born with multiple horns. Sometimes an animal grows a lot of horns, like eight, but usually it’s three, four, five, or six.

Another animal with more than two horns is the four-horned antelope that lives in India and Nepal. Its horns are quite small, just a pair of tiny points on the forehead with a pair of longer points behind them. The antelope itself is also small, not much more than two feet tall at the shoulder, or 60 cm. Its coat is reddish or yellowish-brown with white underparts, and a black stripe down the front of the legs. The longer horns grow up to about five inches long, or 12 cm, but the front horns are no longer than two inches, or five cm.

The four-horned antelope is shy and solitary, and lives in open forests near water. Since it’s so small, it frequently hides in tall grasses. Sometimes a four-horned antelope’s front two horns are just bumps covered with fur, which makes them look like ossicones although they’re still actually horns.

That brings us to the other group of animals with multiple horns, although they’re not actually horns. I mentioned ossicones in the tallest animals episode, about giraffes. They’re made of ossified cartilage instead of bone, and are covered in skin and fur instead of a keratin sheath. Antlers are actually very similar to ossicones in many ways. A deer’s antlers grow from a base that is similar to an ossicone, and as they grow, the antlers are covered with tissue called velvet that later dries and is scraped off by the deer to show off the bony antlers. Unlike horns, which are always unbranched, the ossicones of some extinct animals can look like antlers.

We talked about sivatherium in episode 256, about mammoths. It was an ancestor of modern giraffes that lived in Africa and India around a million years ago. It stood around 7 feet tall at the shoulder, or just over two meters, but had a relatively long neck that made it almost 10 feet tall in total, or about three meters. It had two pairs of ossicones, one pair over its eyes and another between its ears. Like the four-horned antelope, the front pair were smaller than the rear pair, but the rear pair was broad and had a single branch.

Sivatherium was once believed to be closely related to elephants, and reconstructions of it often made it look like a moose with a short trunk. But modern understanding of its anatomy suggests it looked like a heavily built giraffe with shorter legs and neck, sort of like the giraffe’s closest living relative, the okapi.

One interesting thing about Sivatherium is how recently it may have been alive. Some researchers think it may have been around only 8,000 years ago. There’s rock art in India and the Sahara that does seem to show a long-necked animal with horns that isn’t a giraffe. The art has been dated to around 15,000 years ago. But the big controversy is a figurine discovered in 1928.

That’s when a copper rein ring was found in Iraq and dated to about 2800 BCE. A rein ring was part of the harness to a four-wheeled chariot, with two holes to thread the reins through to keep them from tangling. Above the rings was a little decorative figure of an animal. This particular rein ring’s figure shows an animal with short horns above the eyes and branching horn-like structures farther back, between the ears. When it was originally discovered, scientists thought the figure represented a type of fallow deer found in the area, with the ends of the antlers broken off. But one researcher, Edwin Colbert, pointed out that no deer known has four antlers and the figure clearly has two little bumps over its eyes that are separate from the branched antler or horn-like structures farther back. In 1936 he published his conclusion that the animal wasn’t a deer at all but sivatherium, and a lot of scientists agreed.

That would mean sivatherium might have been alive less than 5,000 years ago. Part of the issue is that sivatherium’s branched ossicones weren’t very big in comparison to its head, while the fallow deer’s antlers are proportionally quite large. The figurine has structures that match sivatherium’s ossicones more than a deer’s antlers. But in 1977, two little pieces of copper were found in a storage box where they’d been since the original discovery of the rein ring. The pieces fit exactly onto the ends of the figure’s horns, showing that the horns are much bigger than originally thought.

That doesn’t explain everything, though. The figure still has those extra little horns over its eyes, and while the branched horns look like deer antlers, they still don’t look like fallow deer antlers. Some researchers point out that sivatherium had a lot of variation in the size and shape of its ossicones, too.

Ultimately there’s not enough evidence either way of whether the figurine depicts a deer or sivatherium. If sivatherium did live as recently as a few thousand years ago, hopefully remains of it will be found soon. Until we know for sure, you can still be glad that the giraffe is alive, because it’s just as amazing as its extinct relation.

You can find Strange Animals Podcast at strangeanimalspodcast.blubrry.net. That’s blueberry without any E’s. If you have questions, comments, or suggestions for future episodes, email us at strangeanimalspodcast@gmail.com. We also have a Patreon at patreon.com/strangeanimalspodcast if you’d like to support us for as little as one dollar a month and get monthly bonus episodes.

Thanks for listening!

Episode 353: Warm-Blooded Fish

Posted on by

Podcast: Play in new window | Download (Duration: 9:41 — 11.4MB)

Subscribe: RSS | More

This week we’re going to learn about some fish that feature warm-bloodedness! Thanks to Eilee for suggesting the moonfish, or opah.

Further reading:

Are all fish cold-blooded?

The Opah Fish Is Warm-Blooded!

Basking Sharks Are Partially Warm-Blooded, New Research Suggests

Megalodon Was Partially Warm-Blooded, New Research Shows

The opah, or moonfish, looks like a pancake with fins but is an active swimmer [picture from first article linked above]:

An opah not having a good day [photo by USA NOAA Fisheries Southwest Fisheries Science Center – https://swfsc.noaa.gov/ImageGallery/Default.aspx?moid=4724, Public Domain]:

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

Months ago now, Eilee suggested we talk about the sunfish. We’re actually not going to talk about the sunfish this week, although it is on the list to cover eventually. Instead, we’re going to talk about something else in Eilee’s email. Eilee asked if there was a moonfish too, and not only is there a moonfish, it’s basically the most unique fish alive today in one particular way. It’s warm-blooded!

The moonfish is also called the opah. It’s golden-orange in color with little white spots, and it’s very round and flattened side-to-side, like a pancake with orange fins. It has big golden eyes and a tiny mouth. It’s also quite large, with the biggest species growing up to 6 and a half feet long, or 2 meters. That’s a really big pancake. It lives in the ocean, sometimes diving deeply, and despite looking like a pancake, it can swim very quickly to catch squid and small fish. It also eats krill. The reason it can swim so quickly is because it has huge muscles that power its fins, and the muscles also generate a lot of heat, enough to keep its entire body at least several degrees warmer than the surrounding water. This is a warm-blooded trait, but fish are supposed to be cold-blooded.

The scientific term for warm-bloodedness is endothermy. Mammals and birds are endothermic, meaning our internal body temperature stays roughly the same no matter what temperature it is outside. Cold-bloodedness, called ectothermy, means an animal’s internal body temperature fluctuates depending on the temperature outside its body. Reptiles, amphibians, fish, and invertebrates are all cold-blooded.

To us as mammals, it feels like warm-bloodedness is a really good idea, but it comes at a high cost. Mammals and birds have to eat a lot more and a lot more often than cold-blooded animals do, because keeping our body temperature steady takes a whole lot of energy. An endothermic animal generates heat mainly by metabolizing food, although muscle movements like shivering and running also generate heat. An endothermic animal can be as active at night as it is during the day, and can be as active in winter as it is in summer.

Some otherwise cold-blooded animals can generate enough heat with muscle movements to warm parts of the body, called regional endothermy, or can generate heat with muscle movements in certain situations, called facultative endothermy. The female of some species of snake, especially some pythons, will wrap her body around her eggs and shiver, which generates enough heat to keep the eggs warm. Bumblebees can also shiver to warm their bodies enough to allow them to fly in cold weather. At least some species of sea turtle, including the green sea turtle and the leatherback, generates enough heat in its muscles while swimming that it’s able to migrate long distances in very cold water. Some scientists think all marine reptiles may be regional endotherms to some degree.

Some fish demonstrate regional endothermy too. So far, 35 species of fish are known to be partially warm-blooded, including some species of tunas, sharks, and billfish. Scientists originally thought that only predatory fish needed the extra boost of speed and endurance that endothermy provides, but then they discovered the basking shark is regionally endothermic, and the basking shark is a filter feeder that doesn’t need to chase after fast-moving fish. Also, almost nothing eats it, so it’s not running from anything either.

The basking shark is also huge, one the largest sharks alive today. It can grow over 40 feet long, or more than 12 meters, and possibly longer, although most individuals are closer to 25 feet long, or around 7 1/2 meters. It mostly lives in cold waters, sometimes diving quite deeply but sometimes feeding at the surface of the ocean. It just goes where it can find lots of tiny food that it filters out of the water with structures called gill rakers. The basking shark just swims forward with its gigantic mouth open, water flows through its gills, and the gill rakers catch any tiny particles of food. The gill rakers funnel the food toward the throat so the shark can swallow it. It mostly swims slowly and isn’t a threat to anything in the ocean except the tiniest of tiny animals. So why does it need parts of its body to be warmer than the water it’s in?

Scientists think it may have something to do with how far the basking shark travels in a year, since endothermy provides more energy for endurance swimming. The basking shark migrates thousands of miles, presumably following the best conditions to find plenty of food, although we don’t know for sure. It could be that it prefers a specific type of environment to breed or have babies. In the summer basking sharks do congregate in groups even though the rest of the year they’re solitary. The female retains fertilized eggs in her body, where the eggs hatch and the babies continue developing until they’re born a few months later. Scientists think the unborn babies eat unfertilized eggs after the food in their yolk sacs runs out.

The basking shark is critically endangered and is protected in many countries, but because it migrates such long distances it doesn’t always stay where it’s safe. Learning more about it helps conservationists know how best to protect it, and that’s how scientists discovered it was regionally endothermic. It generates heat from muscles deep inside its body as it swims, which helps keep its organs warmer than the surrounding water.

Other sharks are known to share this trait, and in June of 2023, a new study about megalodon indicated that it was probably regionally endothermic too. Megalodon went extinct almost 4 million years ago and was so big that it makes even the largest great white shark look like a teeny little baby shark. I may be exaggerating a little bit. The great white’s teeth grow around 2 and a half inches long, or a little over 6 cm. Megalodon’s teeth were 7 inches long, or 18 cm. We don’t know how big Megalodon’s body was, but it could probably grow at least 34 feet long, or 10.5 meters, and possibly grew as much as 67 feet long, or 20 meters. It ate whales. Like the basking shark and some other living sharks, including the great white, the heat generated by its muscles as it swam would have kept its internal organs, eyes, and brain warmer than the water around it.

But the opah takes this a step farther. Instead of keeping parts of its body warm, it’s just full-on endothermic. It’s warm-blooded. It mainly generates heat by moving its muscles, and it retains heat with a layer of special fatty tissue around its gills, organs, and some muscles. It also has a heat exchange system in its blood vessels that’s incredibly efficient. Cold water flowing through the gills chills the blood, but as the chilled blood flows deeper into the body, it’s warmed up by passing closely alongside heated blood flowing out from the heart. As a result, the opah can maintain its body temperature even when spending lots of time in cold water.

We actually don’t know that much about the opah, even though it’s a fish people like to catch and eat. It was described scientifically in 1799, which means it took well over 200 years for scientists to figure out that it was a warm-blooded fish. That means it’s very likely that it’s not the only endothermic fish alive today, it’s just the only one we’ve found so far.

You can find Strange Animals Podcast at strangeanimalspodcast.blubrry.net. That’s blueberry without any E’s. If you have questions, comments, or suggestions for future episodes, email us at strangeanimalspodcast@gmail.com. We also have a Patreon at patreon.com/strangeanimalspodcast if you’d like to support us for as little as one dollar a month and get monthly bonus episodes.

Thanks for listening!