Monthly Archives: January 2025

Episode 417: The Hoatzin

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I’m a bit under the weather this week, so here’s a Patreon episode about a weird bird!

Further reading:

Hoatzin nestling locomotion: acquisition of quadrupedal limb coordination in birds

Show transcript:

Welcome to the Patreon bonus episode of Strange Animals Podcast for mid-November, 2019!

We’re going to learn about a mystery bird today. When I say mystery bird, I don’t mean that people aren’t sure if it exists. It definitely exists. You can go to South America and look at it if you like, because fortunately it’s not rare or endangered. But scientists aren’t completely sure what it’s related to, because it’s a really weird bird.

The hoatzin [pronounced what-seen] is a large bird, over two feet long, or 65 cm. It’s shaped sort of like a pheasant, with a chunky body, long neck and small head, and a long tail made of stiff feathers like a hawk’s. Its face has no feathers and blue skin, it has red eyes, and it has a spiky feather crest on its head. It’s black and chestnut brown with some darker and lighter streaks, and is a softer brown underneath. It’s a really pretty bird, in fact, with a strong bill. But it really doesn’t resemble any other bird alive today.

The hoatzin is the only species in its genus, and the only genus in its family, and the only family in its order. It’s basically not really related to any other bird alive today, although in 2012 its genome was sequenced and found to be most closely related to cranes and plovers—but only very distantly. In fact, a 2015 study determined that the hoatzin started evolving separately from other birds 65 million years ago, right after the Cretaceous-Paleogene extinction event that killed off the non-avian dinosaurs.

We only have a few fossils of hoatzin ancestors, but they show that it was much more widespread in the past and lived in what is now North America and Europe. But these days it only survives in northern and central South America. It likes swampy areas and forests near rivers or other water.

The hoatzin eats plants—specifically leaves and buds, although it also eats some flowers and fruit. And leaves require a lot of digesting before the body can make use of the nutrients. The hoatzin’s digestive system is unlike any other living bird’s, because the hoatzin is a foregut fermenter. Its crop, which most birds only use to store extra food temporarily when the stomach is full, acts as a bacterial fermentation chamber—two chambers, in fact, since it’s divided into two sections. This acts like the rumen of a cow. Its crop is so big it doesn’t have room on its body for big flight muscles, so it’s not a strong flyer. It mostly stays in trees and bushes, eating leaves, flapping its big wings for balance and display, and hanging out with other hoatzins.

The hoatzin’s digestive system has a weird side effect. It smells bad. It’s supposed to smell like manure. It’s sometimes called the stinkbird and, fortunately for the hoatzin, almost no one wants to eat it as a result.

As you probably know, birds developed from dinosaurs. It’s easy to forget that, since birds have evolved structures like toothless beaks and front legs modified for flight and they no longer have lizard-like tails. But the hoatzin retains something from its dinosaur ancestry that is a startling reminder.

The hoatzin is a social bird that lives in small flocks. It breeds during the local rainy season and builds its nest over water when the forest floods due to rain. The female lays two or three eggs, and when the babies hatch, they can climb around in the branches near the nest right away. This means they can hide from predators instead of being helpless in the nest. And the reason a hoatzin chick can climb so well is partly because it has big feet, and partly because it has finger claws on its wings: specifically a thumb claw and one finger claw, which are fully functional and make it look a lot like a fuzzy baby dinosaur.

Not only does the baby hoatzin use these claws for climbing, a study published in May 2019 shows that the baby hoatzin uses its wings differently when climbing than it does as an adult bird. Obviously, birds fly by flapping both wings at the same time. But the baby hoatzin climbs by using its limbs in an alternating motion. You know, the way you would climb a tree. Or the way a small dinosaur would climb a tree.

But primitive and dinosaur-like as this trait is, researchers have discovered that it developed relatively recently. That is, as the hoatzin’s distant ancestors evolved from a small dinosaur into a primitive bird, it lost the claws on its front legs as they became more and more modified into wings. But at some point, the hoatzin re-developed those claws. Researchers think it’s what is called an atavistic trait, which you may remember from way back in the Patreon episode where we talked about horses with extra toes. In other words, the genes to grow claws on the front limbs are still present in birds, but are suppressed by other genes, since claws just get in the way when you’re flying. But occasionally a small mutation causes the claws to grow anyway, and in the case of the hoatzin, it proved so useful that those babies with claws survived better than those without claws, and therefore lived to pass on their genes. But the claws are no longer useful once the babies grow up and learn how to fly, so they lose them as adults.

Hoatzin chicks climb using alternating motions of the wings, but swim by moving both wings together. Oh, didn’t I mention that the babies swim? They have to, because sometimes a predator attacks and they have to get away fast. They can’t fly yet, and they can’t climb all that quickly, so they drop out of the branches and fall into the water below. That’s why the parent birds build the nests over water. The babies can swim just fine, and they swim to safety and climb back up into the branches where their parents can find them.

The hoatzin isn’t the only bird that has wing claws as a baby. Some species of turaco do too. The turaco lives in Africa and shares many traits with the hoatzin, so for a long time people thought the two were related. But now we know they’re not and that the similarities are due to convergent evolution.

Thanks for your support, and thanks for listening!

Episode 416: The heaviest tarantula and the bitey-est ant

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Thanks to Siya, Sutton, Owen, and Aksel for suggesting this week’s topic, the Goliath birdeater tarantula and the fire ant!

Further listening:

The TEETH Podcast

Further reading:

Tropical fire ants traveled the world on 16th century ships

The Goliath birdeater tarantula, bigger than some kittens:

Fire ants:

Show transcript:

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

This week we’re going to talk about two invertebrates, a spider and an insect. Thanks to Siya, Sutton, Owen, and Aksel for suggesting them!

We’ll start with the spider, which Siya and Sutton both suggested. It’s the goliath tarantula, also called the goliath birdeater. You know it has to be a big spider if it’s called a birdeater. We’ve talked about it before, but not in a long time.

The goliath birdeater is the heaviest spider in the world. If you think of the usual spider, even a big one, it’s still pretty lightweight. Let’s use a wolf spider as an example, which is found just about everywhere in the world. It’s a hunting spider that doesn’t spin a web, and while different species vary in size, the biggest is the Carolina wolf spider found in many parts of North America. A big female can have a legspan of four inches across, or 10 cm, with a body up to an inch and a half long, or 35 mm—but it weighs less than an ounce. That’s barely 28 grams, or just a little heavier than five sheets of printer paper.

In comparison, the goliath birdeater tarantula can weigh over 6 ounces, or 175 grams. That’s heavier than a baseball, or two packs of cards. Its legspan can be as much as 12 inches across, or 30 cm with a body length of about 5 inches, or 13 cm. It’s brown or golden in color and lives in South America, especially in swampy parts of the Amazon rainforest. It’s nocturnal and mostly eats worms, large insects, other spiders, amphibians like frogs and toads, and occasionally other small animals like lizards or even snakes. And yes, every so often it will catch and eat a bird, but that’s rare. Birds are a lot harder to catch than worms, especially since the Goliath birdeater lives on the ground, not in trees.

Because it’s so large, the goliath looks like it would be incredibly dangerous to humans. It does have fangs and can inflict a venomous bite, but it’s not very strong venom. The danger comes from a very different source, because the goliath birdeater is famous for its urticating spines.

Many species of tarantula have special setae, hairlike structures called urticating spines, that can be dislodged from the body easily. If a tarantula feels threatened, it will rub a leg against its abdomen, dislodging the urticating spines. The spines are fine and light so they float upward away from the spider on the tiny air currents made by the tarantula’s legs, and right into the face of whatever animal is threatening it. The spines are covered with microscopic barbs that latch onto whatever they touch. If that’s your face or hands, they are going to make your skin itch painfully, and if it happens to be your eyeball you might end up having to go to the eye doctor for an injured cornea. Scientists who study tarantulas usually wear eye protection.

The goliath birdeater tarantula is considered a delicacy in northeastern South America. People eat it roasted. Apparently it tastes kind of like shrimp.

Next, Owen and Aksel wanted to learn about fire ants. I couldn’t believe that we’ve never talked about fire ants before!

Fire ant is the name for any of the more than 200 species in the genus Solenopsis, but it’s typically used to refer to the species Solenopsis invicta. It’s native to tropical South America but has been introduced to parts of North America, Australia, China, Taiwan, India, Africa, and many other places where the climate is tropical or sub-tropical.

The fire ant initially became so invasive due to Spanish galleons in the 16th century, which carried trade goods around the world. A ship that’s meant to carry a lot of cargo is built so that it needs to be weighted down to a certain degree to sail safely. A lot of times if a Spanish ship didn’t have enough goods in its hold to make it weigh enough, the captain would bring a few tons of soil onboard to make up the difference. Then, when the ship got to its next port where it was supposed to pick up new cargo, it would just dump the dirt wherever it was. It didn’t matter to the fire ant if the dirt was dumped into the water, because fire ants are prepared for their nests getting flooding. They cling together and form huge rafts that the wind pushes to shore. But more often, the dirt would get dumped on land for other ships to re-use.

A team of scientists figured out where the invasive fire ant populations came from by comparing the genetic signatures of 192 different populations. They hypothesized that the ants with the highest genetic diversity were the original population, and that as the ants were moved around the world by ship, genetic diversity would get lower and lower, since all the ants were descendants of the original colony or colonies transported accidentally in the dirt. They mapped out the genetics, then compared the results to Spanish trade routes in the mid-1600s, and it all matched up.

The fire ant made it to the United States in the late 1930s or early 1940s, the West Indies around 1980, and Australia around 2001. These days a lot of fire ants end up transported to new areas in golf course sod imported from Florida.

A fire ant colony consists of a queen, thousands of worker ants, and larger soldier ants that protect the workers and especially the queen. Some colonies have more than one queen. The ants eat anything, including seeds and insects, and even small animals, but also including dead animals they find. The colony can have as many as a quarter million ants. The nest is underground and entrances can be far from the nest itself, and nests can be so large that they can cause structures built over them to collapse.

Invasive animals of any kind aren’t good for the native animals, and the same is true for the fire ant. The fire ant specializes in colonizing areas where humans have disturbed the ground, whereas native ants often have trouble surviving in disturbed areas. The fire ants crowd out native ants and can destroy some native plants.

But the main reason why people don’t like fire ants is that they bite and they’re venomous. The bites cause a burning sensation and painful swelling, but some people are allergic to the venom and can actually die from ant bites. Luckily, that’s rare, but the bites are still painful.

Some countries have spent millions of dollars trying to eradicate the fire ant, including Australia and New Zealand. New Zealand seems to have succeeded, but Australia is still struggling to get the invasion under control. Fortunately, a lot of animals eat fire ants, which helps. One of the animals that especially loves to eat fire ants is the wolf spider, so now we’ve come full circle in this episode.

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!

If you are wishing that I’d gone into more detail about fire ant attacks, you might like the TEETH podcast. It’s the only podcast where you’ll hear wild animal attack stories directly from the survivors, hosted by a wilderness guide and attack survivor himself. I’ll put a link in the show notes so you can go listen. It’s appropriate for all ages. I don’t think they’ve actually covered a fire ant attack, but they’ve got lots of other fascinating accounts.

Episode 415: Animals with Names

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This week we’re going to learn about some animals that seem to have individual names!

Further reading:

Bottlenose dolphins can use learned vocal labels to address each other

How Do Dolphins Choose Their Name?

Vertical transmission of learned signatures in a wild parrot

Baby Parrots Learn Their Names from Their Parents

Study: African Elephants Address Each Other With Name-Like Calls

Marmoset Monkeys Use Names to Communicate with Each Other

The green-rumped parrotlet (photo by Rick Robinson, taken from this site):

Show transcript:

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

This week we’re going to learn about some animals that seem to be using names to refer to other individuals or themselves.

Let’s start with bottlenose dolphins, because they’re well-studied and scientists have known about this particular aspect of their society for over a decade. Every bottlenose dolphin has a signature whistle that identifies it to other dolphins. The signature whistles can be complex and the dolphin may add or change details to indicate its mood or other information. It’s not precisely a name in the way humans would think of it, but it is an identifier.

The dolphin creates its own signature whistle when it’s young. Some dolphins pattern their whistles on their mother’s signature whistle, while others mimic their siblings or friends. Some seem to pattern theirs on a distant acquaintance, which sounds to me like they just like something about an unusual whistle and decide to incorporate it into their own whistle. As dolphins grow up, females typically don’t change their whistles, but males often do. Male dolphins often pair up together and remain bonded, and a pair may change their signature whistles to be similar.

When a dolphin is trying to find a friend it can’t see, it will mimic that friend’s signature whistle. If a mother can’t see her calf and is worried, she’ll do the same, and her calf will answer by repeating its signature whistle. A lost calf will imitate its mother’s whistle. But it’s even more complicated than it sounds, because a group of dolphins who get together to forage may choose a shared whistle that the whole group uses. This helps them coordinate their behaviors to work together. Each member of the group uses a slightly different version of the group whistle, which means that each member can identify who’s speaking.

Other cetaceans seem to use a similar kind of name. Sperm whales, for instance, have a unique click sequence that they use to announce themselves when approaching other whales. The signature clicks always appear at the beginning of a sequence and don’t vary.

Bottlenose dolphins and many other cetaceans are extremely social animals. So are parrots. Studies of parrot calls indicate that parrots appear to have signature calls that they use the same way as dolphins do, to identify themselves to other parrots and as a way for other parrots to call for them. A study of wild green-rumped parrotlets in Venezuela discovered that the birds give a unique signature call to each baby while it’s still in the nest, and the baby continues to use its call its whole life, often with small changes.

The study set up video cameras to monitor 16 nests of a large wild population of the parrots. The population has been well studied and is used to using nesting tubes that scientists have set up for them. This makes it easier for the scientists to monitor nesting behaviors. In this case, to test whether the names had something to do with genetics or not, the scientists sneakily moved half of the eggs from one nest to another, so that half the parents unknowingly raised some chicks that weren’t actually related to them.

Despite the egg switcharoo, all the chicks were given names that were similar to the parents’ signature calls. The parents started using a specific signature call soon after the eggs hatched, and the babies started imitating it. Gradually each baby added its own specific flourish to the call that made it their own, so while you can say that the parents named their babies, it’s just as true to say that the babies named themselves. The parrots use the signature calls to announce themselves, but also to call for friends, siblings, and parents.

Elephants are also extremely social animals. Recent studies of African savanna elephant calls indicate that elephants also have an identifying rumble sound that acts as a name. In fact, it acts more like a name as humans use names than the signature sounds made by dolphins and parrots. An elephant will use a specific rumble when addressing another elephant, but the rumble isn’t the speaker’s name, it’s the recipient’s name. It’s the difference between me saying, “Hi, I’m Kate. How are you?” and me saying, “Hi, Kelly, how are you?” when I’m talking to my friend Kelly. Dolphins and parrots seem to be saying something like, “Kate here, I’m swimming this way.”

Marmosets seem to use names the same way that elephants do. Marmosets are a type of small monkey native to Central and South America, which live in treetops and eat fruit and other plant material, and the occasional insect. A 2024 study found that marmosets that know each other address individuals with specific sounds, whether or not they’re related.

All the animals we’ve talked about today are incredibly social, just like humans are. In the case of dolphins, parrots, and marmosets in particular, it’s easy for individuals to travel and forage together but be out of sight of one other. Having a way to track friends and family members when you can’t see them is important to keep a group together.

Studies about animals using names are becoming more common, with both the marmoset study and the elephant study published in 2024. It may not seem like a big deal, but using a specific vocal label for a specific individual is a huge indicator of linguistic intelligence. We haven’t known a lot about it before recently because the recordings of animals communicating was time-consuming and difficult to categorize. Now we have sophisticated computer programs that can compile the information for us, so that scientists can study it more easily. I wouldn’t be a bit surprised if more and more studies start finding animals that use names.

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 414: Two Marvelous Frogs

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Thanks to Eilee and Alexis for their suggestions this week, two amazing frogs!

Further reading:

Paradoxical frog: The giant tadpole that turns into a little frog

Fungus is wiping out frogs. These tiny saunas could save them.

How to build a frog sauna

The paradoxical frog [photo by Mauricio Rivera Correa – http://calphotos.berkeley.edu, CC BY-SA 2.5, https://commons.wikimedia.org/w/index.php?curid=6703905]:

The Vietnamese mossy frog [photo by H. Zell – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=81804225]:

Show transcript:

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

Let’s start 2025 off right with an episode about frogs! Thanks to Alexis and Eilee for their suggestions.

Let’s start with Eilee’s suggestion, the paradoxical frog. The paradoxical frog is a type of tree frog that lives in South America. Like other frogs, it likes ponds and shallow lakes. Some individuals are green and some are brown, and a frog may have darker stripes or splotches, or might just be plain. The tadpoles eat algae and other tiny food, while the adults eat insects.

As with most frogs, the paradoxical frog hatches into a larval stage called a tadpole or pollywog, which is fully aquatic. It later metamorphoses into its adult form as a frog. Most tadpoles start out very small and grow larger, then metamorphose into a juvenile frog which then grows to fully adult size. But while the paradoxical frog’s tadpole starts out small, it can grow to as much as 11 inches long, or 28 centimeters! It’s the largest tadpole in the world as far as we know.

So how big is the adult frog if the tadpole is so enormous? About 3 inches long, or 7.5 cm, from snout to vent. That’s why it’s called the paradoxical frog, because a paradox is something that seems contradictory to expectations. Instead of the ordinary way of things, where a small tadpole grows into a bigger frog, in this case a big tadpole grows into a smaller frog. It’s sometimes called the shrinking frog.

One interesting detail is that not all of the tadpoles are that big. If a female lays her eggs in a small body of water that’s likely to dry up, or that doesn’t have a lot of food available, or if there are a lot of predators in the water, the tadpole metamorphoses quickly and doesn’t grow very big. But if the tadpole is in a better location it matures much more slowly, which allows it to reach much larger size before metamorphosing.

I should also mention that the 11-inch-long tadpole that is the largest ever measured was actually raised in captivity. In the wild, the largest paradoxical frog tadpole ever measured was 6 ½ inches long, or almost 17 cm. That’s still really big, but not that ridiculously big. But the confusing thing is that the tadpole is big and bulky, up to four times the size of the adult frog. Where does all that mass go after it transforms?

Early scientists who learned about the paradoxical frog wondered the same thing. They were so confused that they suggested that the frog actually came first and later metamorphosed into the tadpole, which then metamorphosed into a fish. But the main reason the tadpole is so long is its tail. When it metamorphoses into a frog, it absorbs the tail and therefore appears to shrink. The bulkiness of the tadpole’s body matches the bulkiness of the frog’s body. And unlike most frogs, which metamorphose into juvenile frogs that still have some growing to do, the paradoxical frog metamorphoses into a completely adult frog. It’s as big as it will ever get and fully mature, ready to mate and lay eggs.

Next, Alexis wanted to learn about the Vietnamese mossy frog. It lives in parts of Vietnam, Laos, and other nearby areas. It prefers mountainous rainforests and the female often chooses to lay her eggs in a tree hollow or even a rock cavity where water has collected. Instead of laying her eggs in the actual water, though, she lays them on rocks or branches above the water. The eggs don’t dry out because of the high humidity in rainforests, and when they hatch, the tadpoles fall into the water.

The tadpoles take a long time to mature, anywhere from four to eight months depending on how warm it is while they’re developing. They grow quite large, although not anywhere near the size of the paradoxical frog tadpole.

A big female Vietnamese mossy frog can grow up to 3 ½ inches long, snout to vent, or 9 cm, and is chubby and round. It’s nocturnal and spends the day hiding on mossy rocks or among plants in the water, then comes out at night to hunt insects like crickets as well as other small animals like worms.

The reason it’s called the mossy frog is because it looks for all the world as though this frog is covered in moss, or maybe is just made out of moss. It’s green and brown in color and its skin is covered in little bumpy structures called tubercules. This helps it blend in incredibly well in the rainforest, where moss is pretty much everywhere. If it feels threatened and it can’t jump into the water to hide, it will play dead.

This is what a Vietnamese mossy frog sounds like:

[frog beeping]

As we’ve talked about in other frog episodes, frogs throughout the world are declining in numbers because of a fungus that infects their skin. The effects of this fungus are worse in cold weather, so a team of scientists speculated that helping the frogs stay warm might help them stay healthier in winter and even help them recover from the infection. They tested their hypothesis by offering infected frogs a variety of temperatures in their enclosure. The frogs could pick where they wanted to spend their time. The frogs liked the warm areas but didn’t spend all their time in them, but they all recovered from the infection. Frogs who were given an overall warm environment also recovered, but not as fast. Frogs who had an ordinary enclosure without warmer areas remained infected with the fungus. Even better, frogs who had recovered from infection with the warm environment also showed resistance to later infections.

The team worked to develop plans that allow people to easily build what they call frog saunas. They don’t require electricity or fuel, just sunshine. When the saunas are placed near ponds or other areas with frogs, the frogs find them quickly and use them. There’s a link in the show notes if you want to learn how to make a frog sauna for your own back yard.

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!