Readers’ wildlife photos

December 23, 2020 • 8:00 am

Biologist John Avise has contributed some non-duck and non-faux-duck photos for today’s feature, which one could call “Three Ways of Looking at a Gull”. His notes and captions are indented; click on the photos to enlarge them.

I’m heeding your call for more photos to add to your Readers’ Wildlife Photos bin.  This time, I tell the stories of three recent encounters I’ve had with a local gull species.

Three Stories of Western Gulls (Larus occidentalis)

Most of the time, members of this common species in California rest quietly on land or fly around lazily.  But every once in a while, their wilder side comes out and is on full display.  The captions of the following sequences of photos tell three such stories: (1) a drag-out fight between two birds; (2) the killing and eating of a wild octopus; and (3) scavenging the remains of a dismembered lobster cadaver.

A flock at rest:

A bird in flight:

It started out peacefully:

But then one bird got agitated…:

And attacked the other:


Things escalated…:

And grew more serious…:

And more serious…:

As one bird nearly drowned…:

But managed to keep his head out of the water:

She’s caught a live octopus:

The octopus tries to escape…:

But it’s no use…:

The gull kills the octopus:

It’s all over now:

Except for the swallowing:

The octopuses’ last sight:

She’s found a lobster shell on the beach:

Might there be goodies left inside?:

Yes, and even more meat in the tail:

Portrait of a satisfied bird:

True facts about army ants and their associates

December 17, 2020 • 2:30 pm

ZeFrank’s videos are getting better and better as he adds more biology, talks to experts in the field, and puts in professional videos taken by biologists. This one, about army ants, is especially good. Ants are strange anyway, but army ants, which have no permanent nests (often living in vans down by the river), are among the weirdest ants. We have them in the U.S., too, though you don’t often see them and they’re being extirpated by imported fire ants.

There’s a new book out on army ants (click on screenshot below), and though I haven’t read it, my ant friends (not ants, but people who work on them) say it’s excellent and especially well written.

As I said, army ants have no permanent nests, and are always on the move, though they move in a punctuated fashion, sometimes staying put for a while, but never living underground. Each nest has a single queen, and if that queen is killed by predators or dies, the nest is a goner, for the colony simply can’t function, plus it loses the only individual who can produce new ants. Male ants (drones) do no work, but march with the colony, and when it’s time to reproduce they fly away (they have wings) and find virgin queens in another nest.

Besides the reproductive queen, there are a few non-mated queens in each nest, and those come about when workers “decide” to give a few larvae extra food (probably richer food, too, as is done with “royal jelly” in bees). Those female larvae, coming from fertilized eggs (males, as in all Hymenoptera, develop from unfertilized eggs), become queens, and, when they’re ready to mate, emit a pheromone. That pheromone attracts the winged drones from other swarms, who fly to the other swarm and mate with the virgin queens, dying soon thereafter.

This produces an army-ant swarm with more than one queen, and that’s an intolerable situation for the workers. Thus such swarms undergo fission, with the newly-mated queens taking off with a bunch of workers to found their own swarm.  As with bees, the male ants are true drones, doing no foraging and serving only to contribute sperm to unfertlized queens.

One other note: Army ant queens are huge compared to workers, and would make tasty prey for a bird or other predator. That’s why, when the colony is on the move, the queen is surrounded by a retinue of workers, especially the soldiers with their fearsome jaws. Look at this size difference! (This is Eciton burchellii, a neotropical species in the genus most featured by ZeFrank):

Source. Photo by Daniel Kronauer

Here’s a pinned soldier of the species. Look at those jaws!

AntWeb.org image

The queen can lay up to 100,000 eggs in 20 days, and that’s why she needs that huge abdomen.

Here’s a fascinating Attenborough video on army ants:

Readers’ wildlife photos

December 14, 2020 • 8:15 am

We are seriously low on readers’ wildlife photos, and I’m getting quite nervous. Do me a favor and send in your good photos; don’t make me beg! If I have to, I’ll play the my-content-is-free-so-please-send-some-pictures-in-return card.

Today we have contributions from two readers—some photos and a video. The photos come from reader John Egloff, who admits that they’re not the greatest pictures; but I thought they were worthwhile posting, as one rarely sees these nocturnal creatures even though many of us live among them. John’s captions are indented.

 In response to your request for more wildlife photos, I admit to being a bit intimidated by the stunning quality of the photos submitted by others that have appeared on your website.  Although the attached photos aren’t of that quality, I thought your readers might enjoy seeing these pictures of a nocturnal animal that most people never see and (as was originally the case with me) may not even realize is native to the Midwest.

Several years ago, I was living on the third floor of an apartment building on the far north side of Indianapolis that backed up to a woods and river where the wildlife was plentiful.  One evening, after dark, I was grilling on my back patio when something plopped onto the bird feeder a few feet from my head, startling me.   When I turned to look, my first impression was that a mouse, or perhaps even a rat, had jumped onto the feeder.  I watched the creature munch on sunflower seeds for a few minutes when, to my surprise, it simply leapt off of my birdfeeder, some 25 or 30 feet in the air, into the darkness.

Looking through one of my handy wildlife reference books, I discovered that what I had seen was a Northern Flying Squirrel (Glaucomys sabrinus).  Although I had (mistakenly) considered myself to be pretty knowledgeable about our local wildlife, I had been under the impression that flying squirrels were something that existed in the tropics – and certainly not in Indiana.

I soon discovered that these flying squirrels were coming to my birdfeeder every evening as soon as it grew dark.  Perhaps because we were up so high, they didn’t seem to be the least bit afraid of people, and on one occasion when my father was visiting he even (foolishly) reached out and petted one!

Because it was dark, when the squirrels leapt from my birdfeeder I couldn’t really see them “fly.”  In order to try to capture that, I set up a camera and flash on a tripod and aimed the camera into the darkness in the direction where the squirrels seemed to go.  As soon as they leapt from the feeder, I would fire the camera and flash.  Although I ended up with a lot of photos with no squirrel (or sometimes half a squirrel), I did manage to get several shots of the squirrels in flight.  The photos aren’t the sharpest because it was dark and I had to simply guess at a pre-set focal point; they’re also a bit grainy because the image has been enlarged.

Good enough; such photos are quite rare.

And now some videos from reader John Crisp:

Here’s an amazing whale encounter we had on the Fram [JAC: A Hurtigruten polar ship, similar to but smaller than the one I was on last year] in January this year. We were surrounded by an estimated 200 humpback whales (counted by the resident whale researcher). Sorry about the human noises – not just tourists, but half the crew were on the deck, so unusual was the experience! Nonetheless, the roaring of the whales is awe-inspiring. My apologies for the last 20 seconds, where I lost the plot. I should probably edit them…

John added this:

If you think it is suitable for a family show, I also have some remarkable footage of copulating lions…

I’ve asked for that footage but just got it a few minutes ago. The captions:

Lions mating in the Masai Mara. Somewhat voyeuristically, we watched for a while. During the time when a female is receptive, the pair may mate every 20 minutes and up to 50 times in a 24-hour period.

It is a noisy and apparently antagonistic affair! Watch these two:

This one shows afterglow, but no cigarettes:

And a nursing lioness:

 

First report of tool use in honeybees: a native species uses dung pellets to repel predatory wasps

December 13, 2020 • 10:00 am

In my book Why Evolution is True, I begin the chapter on natural selection (Ch. 5) by describing how native honeybees in Asia defend themselves against the attacks of a predatory Asian giant hornet (Vespa mandarina), a species of huge and fearsome hornets that has now invaded North America. (You’ve surely heard of them as “killer wasps” or “murder wasps”: they are so big, vicious, and venomous that their stings kill several dozen people a year.)

These hornets can completely destroy a honeybee hive, as the hornets are impervious to stings and have powerful jaws that can decapitate bees at a rate of more than one a second. After raiding a nest and killing all the residents in an hour or two, the wasps slurp up the bees’ honey and then carry off the bees’ brood to feed their own larvae, who are ravenous for meat.

Wasps find the honeybee nests via scouts, who, upon encountering a nest, mark it and the surrounding vegetation with a pheromone, which somehow attracts other wasps to the nests, often leading to a big raid. (Wasps may also follow the scouts to the nest.)

But natives bees have evolved a counter-adaptation: “balling”. Sometimes, when a scout wasp lands on a nest of native bees, the residents lure the scout inside, where a swarm of bees awaits. They pounce on the scout, surrounding him with a big ball of bees, and proceed to vibrate their abdomens. This raises the temperature inside the ball  to 47°C (117° F), a temperature that cooks the wasp to death within 20 minutes but doesn’t hurt the bees. Here’s a short video of a bee ball killing a hornet, which you can glimpse in the center of the vibrating mass:

It’s a clever and evolved strategy for disposing of a scout before it has a chance to alert other wasps. The wasp’s fearsome behaviors, and the “arms race” that has led to “balling” by the native bees, is the example I use to introduce natural selection.

As you might predict, introduced bees, like the European honeybee (Apis mellifera), haven’t been in Asia long enough to evolve the balling strategy, and thus are much more likely to have their nests destroyed by wasps. Natural selection takes time.

But some native honeybees have evolved (or perhaps learned) another defense against wasps, and this is described in a new paper in PLOS ONE. It in fact involves the first known use of tools in honeybees. Click on screenshot below to read it (pdf is here, reference at bottom):

The title pretty much tells the tale. Here’s the victim honeybee, Apis cerana, a native species (click all photos to enlarge them):

And the main predator studied, Vespa soror, another large fearsome wasp that raids and destroys  the bees’ nests. These are big ‘uns, with lengths ranging from 26-46 mm (1-1.8 inches)

The study was done in Vietnam using commercially kept bees with wooden nest boxes. The researchers observed that many of the nest boxes were speckled around the entrances with tiny raised spots of animal dung, as in picture A below. They observed bees collecting dung (B; note that the B is experimentally marked), and immediately conveying it to the nest entrances, where they worked it into tiny mounds around the entrance.

Photo C shows a worker bee (these are of course all females) with a bit of dung in its mouth. They don’t eat it, but take it to the nest entrances. D shows another marked bee, with the orange spot, plastering the dung by the entrance.

Attacks by wasps and the results are shown in photos E (an attack by six V. soror workers), and F, which shows how the wasps actually enlarge the entrance by chewing on the wood, presumably to allow easier access to other wasps. Those wasp jaws are strong!

The researches did a number of manipulative and observational experiments to answer some questions about this behavior.  I’ll summarize them briefly:

a.) The fecal spotting is widespread. Over the ten-day observation period, the number of hives accumulating spots went from about 10% to between 40% and 90%. This is, perhaps, because the researchers were working during the wet season, when wasp attacks are most frequent.

b.) Attacks by the wasp prompt more fecal spotting of the hives. The spotting occurs either during an attack of wasps who don’t destroy the hive, after an attack when experimenters prevent further attacks, and for at least three days after an attack. The continuation of spot-making after an attack is used as one clue about how the spotting works (see below).

c.) Attacks by a less dangerous wasp species prompt less fecal spotting. Wasps in the species V. velutina don’t attack nests en masse like V. soror, but simply pick up single bees in flight. Sure enough, even when encounters between the bee and these two species were equally frequent, there were significantly fewer fecal pellets deposited by the bees after V. velutina than after V. soror encounters. This of course makes sense if the fecal pellets are put in place to reduce the deadliness of wasp attacks.

d.) Extracts of the wasps’ pheromone glands prompt the bees to make more fecal spots. The researchers pinned pieces of filter paper to the nest saturated with either an ether control (it would evaporate, though) or an extract of the “van der Vecht glands” from the wasps, which are thought to be where the wasps’ “scouting” pheromones are made. (They should have used an organic non-wasp chemical that wouldn’t evaporate.) This chart shows the significant increase of spots prompted by using the gland extract as opposed to the ether control (caption from paper); the experiment lasted only six hours.

This suggests that the wasps’ marking of the nests, as opposed to wasp presence alone, is a main force leading to fecal spotting. You don’t need wasps to create the bees’ behavior, just pheromones.

e. Fecal spotting keeps the wasp V. soror away from nest entrances. The researchers divided nests into three categories with respect to the level of fecal spotting: light, moderate, and heavy, shown respectively by the three colors of bars in the figure below. When they measured the behaviors of the hornets in several ways (duration of visits, —which include visits in which wasps don’t land on the nest box), duration of time wasps were landed on the hive, duration of time at the entrance, and duration of chewing at the entrance, every single index of aggressive wasp behavior decreased with increased spotting. The asterisks below show significant difference between groups, almost certainly due mostly to the light spotted nests versus the group (moderately spotted + heavily spotted).  This shows that the fecal pellets do something to reduce wasp predation.

There are, as the authors note, lots of questions that remain. I’ll deal with only three here:

1.) How, exactly, does the dung reduce wasp visits? There could be two ways. First, the dung could act as a deterrent to the wasps, perhaps via its odor. The researchers could, I suppose, test this directly in the laboratory, but that wasn’t done. The other way is that the dung could mask the “scouting pheromone” deposited by wasps or somehow overpower its odor, reducing wasp attraction. This could in principle be tested by looking at the frequency of wasp visitation on nests where no pheromone had been deposited. But that would be hard to do, as it requires constant monitoring of nests.

The authors favor the idea that the dung itself is a repellent, as the bees continued to add spots around the hive entrance for several days after an attack. (The presumption is that the pheromone odor would have disappeared by then.) But the dung could of course serve both functions.

2.) How did this behavior evolve? I’m assuming here that this is an evolved rather than a learned behavior, though part of it may be learned. There have been reports of this and other wasp species smearing plant juices around the entrances of hives, perhaps using the plants as either a wasp repellent or a pheromone masker. As the authors write:

Fecal spotting is behaviorally analogous to observations of “plant smearing” by Acerana japonica in Japan, which occurs in response to attack by Vmandarinia . In this recently described behavior, workers carry gnawed plant material in their mandibles and then smear their juices around nest entrances, leaving dark stains. Although we did not study how filth foraging is organized, we observed several workers performing “emergency” dances outside of hive entrances, a behavior that recruits nestmates to smear plant material in Japan. It is fascinating that Acerana has been observed foraging for plant material in the northern part of its range and for filth (feces) in the southern part of its range to defend nests against attack by different, but equally deadly, mass-attacking Vespa predators.

It’s possible that the ancestral behavior here is smearing plant juice around nest entrances, especially if you think that animal dung was not as prevalent in the time before bees were kept in boxes by humans or didn’t live around domestic animals. From there it would be a simple step to evolve collecting dung instead of plants, which is easier since you don’t need to gnaw the dung. It’s not clear, of course, whether either behavior is genetic or learned, but I suspect both have a least a partial genetic component. That itself could be tested in principle by seeing if the behaviors appear in bees that are raised “naively”, without the chance to learn from other bees. I don’t know if that is possible.

3.) Is this really tool-using by bees? The authors define “tool use” according to four criteria of Benjamin Beck as published in a 1980 book: an animal uses tools if it uses an environmental object (a piece of dung); if it alters the object in a way to make it more efficient to use (the bees mold the feces and apply them to nest entrances); if the user holds and manipulates the tool before or during use (collection and carrying of feces to nest and deposition as spots); and if the user “effectively orients the tool” (bees place the spots almost exclusively around the nest entrance, which is where predatory hornets enter).  Since the bees do all of these things, the authors conclude that this is a case of tool use—the first known tool use in honeybees (a lot of other insect species use tools).

I’m not so concerned about whether this behavior falls into the category of tool use, whose criteria vary from investigator to investigator, as I am to understand how the “tools” work and how the spotting behavior evolved.

___________________

Mattila HR, G. W. Otis, L. T. P. Nguyen, H. D. Pham, O. M. Knight et al. 2020. Honey bees (Apis cerana) use animal feces as a tool to defend colonies against group attack by giant hornets (Vespa soror). PLOS ONE 15(12): e0242668. https://doi.org/10.1371/journal.pone.0242668

Readers’ wildlife photos

December 10, 2020 • 8:30 am

Evolutionary ecologist Bruce Lyon is back with another fact-filled post with great photos and his own videos. TRIGGER WARNING: consumption of mammals by birds is shown.  I’ve indented Bruce’s commentary, and you can click on the photos to make them bigger.

Herons and egrets with interesting hunting strategies

Here in Coastal California pocket gophers (family Geomyidae) are abundant. These rodents are subterranean but easy to see because they often poke their heads up to the surface when digging burrows—they push dirt from tunnels out onto the ground. Pocket gophers are interesting for several reasons: they are important ecosystem engineers that affect the soil and plants, they destroy garden plants like nobody’s business, and they are a very abundant prey item for lots of predators. And they apparently get their name from fur-lined cheek pouches!

Below is a video of a local pocket gopher that has a collection of tunnels and surface mounds just outside my back door. I am not certain of the species but Botta’s pocket gopher (Thomomys bottae) seems most likely.

Pocket gophers can move a massive amount of earth: one estimate is 2 tons of soil brought to the surface per year per gopher. Since they can be very abundant, this can add up to a big effect at the landscape level. In coastal California, they can be hell on garden plants (they eat the roots), so gardeners often go to great lengths to protect their plants. One defense is a ‘gopher basket’—a wire basket lines a hole and then the plant and soil are put inside the basket. When we first bought our house, we did not always use gopher baskets and as a result lost a bunch of nice plants we had planted, including productive fig and lemon trees. We actually watched the lemon tree tip over and fall to the ground. When we checked it, it had no roots left.

Below: A gopher basket (photo from the web)

Gopher baskets are not the only line of defense—predators are another. Hawks, bobcats, coyotes, and even herons love to eat gophers. Great blue herons (Ardea herodias) have long hunted gophers in the fields around my house. Recently, a particularly tame heron has been hunting in peoples’ yards and because it is so tame I have been able to follow it around and observe and photograph it hunting gophers.

Below: Why did the heron cross the road? To gopher more food. [Example of appalling dad humor I try to inflict on my students.] This heron is right in front of my house.

Below: The heron slowly walks across a neighbor’s lawn after it has detected a gopher. I am not sure if the herons detect the gophers by hearing them moving near the surface or if they see the ground move when the gophers push soil up out of their burrow.

Below: The lunge. The technique is to stab the ground violently with the dagger-like beak. My impression is that they stab the gopher and wound or kill it with the stab. Note that the bird covers it eye with its transparent nictitating membrane during the stab. This translucent covering protects the eye from injury from branches or other sharp things that could damage the eyes.

Below: The attack was successful. This gopher was pretty large—they can get rat-sized. I watched this heron get five gophers in the space of a couple of hours! I suspect the gopher might have had a nest in the general area and was feeding kids.

Below: Another successful stab. This photo clearly shows that the animal had been impaled during the stabbing lunge.

Below: The herons swallow the gophers whole. Sometimes they toss them into the air, like popcorn, and then gulp them down. Other times they work them slowly up the beak to the mouth as this individual is doing.

Below: After several gophers, it is time for some relaxation and preening. Birds have a preen gland that produces waterproofing fats and lots of other goodies—the tip of this heron’s beak is right at the preen gland (on the lower back just where the tail feathers insert in the skin).

Great blue herons are not the only heron-like birds that have interesting hunting techniques. Tool usefoot shaking and providing shade (canopy hunting) have all been documented. Once in a while I see great egrets (Ardea alba) going for gophers but it is rare compared to herons  Egrets have other tricks up their sleeves. One egret at my study area at the university arboretum learned that western fence lizards (Sceloporus occidentalis) are easy pickings, and I watched one egret pick off ten lizards in about 30 minutes. The egret was really tame so I was able to get a couple of videos with my phone. While hunting, the egret constantly swayed its neck back and forth, a behavior that has been discussed on WEIT before but I am not sure if we know why they do this.

Below: Video of the great egret snatching a lizard. Note the swaying neck.

Below: Another video of the same bird.

Below: I have repeatedly seen snowy egrets (Egretta thula) catching fish in an interesting way at Jetty Road, a great birding spot south of Santa Cruz. A few large pipes go under the road to assist with tidal flow in Moss Landing Harbor.  At certain tidal heights the water forms strong whirlpools and the egrets like to grab fish from the whirlpools. I am not sure if they do this because the fish are easier to see or if the whirlpool traps the fish so that cannot escape. Regardless, it is fun to watch. And note the bright yellow feet—this egret species sometimes hunts by shaking its feet in water and I have wondered if the yellow feet help with that in some way.

Below: This egret catches a grunion (Leuresthes tenius) at the whirlpool.

Faux Duck o’ the Week

November 30, 2020 • 8:00 am

I completely forgot about Sunday’s Faux Duck O’ the Week, being occupied yesterday with The Auction and all. But better late than never, and here’s the latest in biologist John Avise‘s series of waterfowl that resemble ducks but aren’t. Can you guess this species?

His captions and Fun Duck Facts are indented. (To see the ID, Fun Duck Facts, and range map, go below the fold.)

At its summer home in Central Alaska:

Close-up in breeding plumage:

Frontal view:

Preening:

With next week’s species to its left:

Click on “read more” for the identification, John’s Fun Faux Duck facts, and a range map: Continue reading “Faux Duck o’ the Week”

The “skunk rat” that chews toxic vegetation and spits the toxins onto its fur

November 27, 2020 • 9:30 am

In various parts of East Africa lives a black-and-white striped rodent, the African crested rat,  Lophiomys imhausi. (It’s also called the “maned rat”.) I call it the “skunk rat” because of its similar black-and-white striped pattern, because, like skunks, it moves slowly (especially for a rodent), and because, also like skunks, encounters with it are unpleasant.

The skunk is protected from predators by its noxious (but non-lethal) squirts from its butt, and it’s evolved a distinctive “aposematic” warning pattern that serves to warn predators to “stay away from me” (predator avoidance can be either learned or genetic). Like the skunk, the crested rat doesn’t need to move quickly, for it has little to fear from predators.

Why does this rat look and act like a skunk? It is in fact a poisonous mammal, and the world’s only poisonous rodent. Some shews, which aren’t rodents, are venomous, but that venom is made by the shrew itself.

The crested rat isn’t inherently poisonous: it becomes so by applying toxic plant compounds to its fur: compounds it gets from chewing the bark of the “poison arrow tree” Acokanthera schimperi (locals use it to make poison arrows, as the poison is stable for decades), and then “anointing itself”, spitting the toxic juice onto certain parts of its coat that it displays when predators are around. Those poisons, which are powerful cardenolides, have killed many a dog, and those dogs who survive subsequently don’t go near the rat, showing that the pattern is easily learned by predators. (Other potential predators of the rat include honey badgers, jackals, servals, hyenas, and leopards.)  Apparently the crested rat is immune to the poison, as it regularly chews on the bark.

It’s a large, long-lived rat, weighing up to a kilogram. Here’s what it looks like:

Here’s the tree, which has poisonous leaves and fruits as well (the rodents appear to use the bark):

Here’s the special line of brown hairs that are displayed and erected when predators are around or the rat is disturbed:

Another view from the paper below (see also the “Trilobite” article from the New York Times, which provided the picture at the top). Note that the hairs in the top photo are erected, like those of a fighting cat, and aren’t visible in the “normal” undisturbed rat shown in the photo at the top of this post. The caption of the pictures below (from the paper) are “An immature Lophiomys imhausi displaying specialized hairs and warning coloration (A) and the same individual (center) with an adult male (top right), and female (top left), from the same trap location. The juvenile is being groomed by the male (B).

Finally, the brown stripe is made of special porous hairs that absorb the toxins, which is why they’re displayed, for this is the part of the rat’s coat that will kill or sicken attacking predators (picture from the NYT):

Here’s a video showing the rat chewing on A. schimperi bark and spreading it on its fur:

Another video showing how absorbent the specialized fur is:

The paper below (click on screenshot to access) is from the Journal of Mammalogy, and the facts above have been known for some time. What this paper does is elucidate some new things about the social behavior of the rats, and provide observations of its grooming behavior, as well as determining whether chewing the plant and applying the toxin to its fur affects the animal’s behavior (it doesn’t). The pdf is here, and the full reference is at the bottom of this post:

Besides providing a good summary of the fragmentary literature on L. imhausi, the paper finds out this stuff:

a). The rat appears social and is probably monogamous. Monogamy is rare for a rodent, and although this is only inferred for this species by repeatedly seeing pairs of crested rats at camera traps or seeing interactions between males and females in captivity, other features of the species, like its large body size, long life, low reproductive rate, and females who are more aggressive than males, are often characteristic of monogamy in mammals.

b.) The species is dense. The authors estimate 4-15 individuals per square kilometer, which is pretty dense. It lives in riparian forest (along rivers), and although the species is labeled “of least concern” by conservationists, its habitat is disappearing and is also patchy, so it may one day be threatened.

c.) Application of the toxins to the fur is sporadic (at least in captivity). Only half of the 22 rats captured and observed, all given fruits, leaves, and bark of the poison arrow tree, applied toxins to their fur. This is no puzzle to me, though it concerns the authors. I suspect it’s because, as the authors suggest, the poisons are stable and long-lived (for decades!), and rats don’t need to keep applying bark juice to their fur constantly.

All of the captive rats got the toxins from chewing bark while ignoring the other bits of the tree.  Here’s a photo of a rat chewing bark (A) and anointing its fur after chewing (B):

So we know a bit more about this species, and although much of what is described in the paper (and in the NYT article) was known before, it wasn’t studied systematically. I for one was unaware of this bizarre rodent. Its existence raises several questions.

Is the chewing and anointing behavior learned or evolved? The authors didn’t test this—or even raise the question—but given that the rats are born with the specialized fur that absorb the poison, I suspect that the chewing-and-anointing behavior is hard-wired. That could be tested by hand-raising newborn crested rats and seeing if they perform the behavior in captivity. If they do, it’s instinctive.

How did the evolution of this behavior evolve? Was the rat immune to the poison from the outset? Since they don’t ingest the bark, how did this whole thing get started? Did a rat chew on some bark, find it unpalatable, and then wipe its mouth on its fur? Such behavior could of course be subject to natural selection, as rats who did this would be less likely from the outset to be eaten by predators.

Once the rat had evolved toxicity, the evolution of aposematic coloration would follow. (The coloration could not evolve before the toxicity-inducing behaviors, as it would make the rat more visible and more likely to be eaten, as it would have no protection.) This is a fairly straightforward evolutionary process, as toxic rats that were a bit more conspiculous would be more easily recognized by predators that had encountered them before, and thus less likely to be attacked more than once by the same predator. Other predators, however, would have to learn one by one—unless (and this is sometimes the case) the predators themselves evolved an innate avoidance to the aposematic black-and-white pattern. This too could be tested by exposing naive predators—ones that had never encountered a crested rat—to one of those rats, and seeing if they instinctively shy away. That is research for the future, and is certainly feasible. While the mechanistic questions are largely answered, the evolutionary questions still dangle tantalizingly before us.

______________

S. B. Weinstein, K. N. Malanga, B. Agwanda, J. E Maldonado, and M. D. Dearing. 2020. The secret social lives of African crested rats, Lophiomys imhausi, Journal of Mammalogy online  https://doi.org/10.1093/jmammal/gyaa127

 

Man reunited with his beloved donkey

November 8, 2020 • 2:30 pm

Given that the Donkey is the symbol of the Democratic party, I thought it would be apposite to end the weekend with this lovely video of a man reuniting with his beloved donkey.

The translations:

Title: “The emotional reunion between a donkey and its owner after confinement”

Why was the donkey confined? I have no idea. But the braying quadruped and its weepy owner have a fantastic reunion.

YouTube notes: “More than two months without seeing the animal in the Malaga town of El Borge and the scene has gone viral on the networks”

Who says animals don’t have emotions of joy? I love donkeys, and used to encounter packs of wild ones when I worked in Death Valley: the feral descendants of prospectors’ animals from the last century or so.

Ants build a hanging, living bridge to raid a hornet’s nest

October 28, 2020 • 2:15 pm

This one-minute video comes with no information about the location or the species of ant, clearly raiding a hornet’s nest for grubs.  What puzzles me is how they built the damn bridge.  If they started on only one side, they’d have no way to go upwards when they reached the bottom. They could start on both sides and join at the bottom, but why, if they wanted to access the nest, did they need a bridge in the first place? Why couldn’t the ants just walk directly to the nest on the ceiling? After all, they seem to cling to the ceiling, at least around the nest, pretty well.

And why did the chain go so low?

I sent the video to a friend of mine who works on ants, and he was mystified as well. Given the lack of notes about the video, he helpfully identified the ant as a New World army ant in the genus Eciton, a denizen of Mexico and South America. They’re known for their raids on wasp nests, and love to abscond with the wasp grubs (you can see that in the video).

But as for why this bridge exists, neither of us knew. So we jointly formulated a theory, which is ours. This was, perhaps, an experiment done by some naturalist, who put a piece of thread in a catenary shape from the edge to the nest to get the ants to crawl along it. But why didn’t the ants just walk directly to the nest along the ceiling? Well, the experimenter could have coated the space between the roof edge and nest with Fluon®, a slippery, Teflon-like substance that insects can’t get a grip on. They would then have to go along the preexisting thread (not visible in the video) to get to the nest. There would be no Fluon on the house side of the nest, explaining why ants are on the ceiling in that area

That’s just one hypothesis, but it’s the only one that makes sense to me. The idea that this was some kind of experiment is also supported by the fact that the video notes have no information in them, nor does the site allow comments.

As for how these ants defeat the wasps, I’m not sure, but this is their lifestyle, and they regularly raid nests like this.

If you have another theory which is yours, by all means put it below.