Enlarge / "They excised what, now?" Puck is nonetheless intrigued by new findings about the mechanisms behind a cat's purr. (credit: Jennifer Ouellette)

There are few things more gratifying to cat lovers than a contentedly purring feline. But the precise mechanisms by which kitties produce those pleasant, low-frequency rumblings has been a matter of some debate among scientists. Now a team of Austrian scientists has determined that connective tissues embedded in cats' vocal cords play a crucial role in this ability, according to a new paper published in the journal Current Biology. The authors argue that their findings call for a reassessment of the current prevailing hypothesis about how cats purr.

Purring is mostly exclusive to cats, although certain other species can produce purr-like sounds, including raccoons, mongooses, kangaroos, badgers, rabbits, and guinea pigs. And cats are usually divided into those that purr ( Felinae ) and those that roar ( Pantherinae ); no cat species can do both. The latter category includes lions, tigers, jaguars, and leopards, and scientists have suggested that the roaring capability is due to an incompletely ossified hyoid bone in the larynx. "Purrers," by contrast, have a completely ossified hyoid, although the purring snow leopard is a rare exception.

We know the fundamental frequency at which cats purr —between 20 to 30 vibrations per second, although purrs can go up to about 150 Hz—but that is lower than expected based on vocal cord anatomy. As a general rule, larger animals have longer vocal cords and thus create lower-frequency sounds. But cats are relatively small, typically weighing on the order of a few kilograms, and their vocal cords are also relatively short. Hence the curiosity about how they produce such low-frequency purrs.

Enlarge / This drake mallard duck has ceased to be! And suffered one final post-mortem ignominy by a fellow duck. (credit: C.W. Moeliker, 2001)

On June 5, 1995, a Dutch ornithologist named Kees Moeliker was working quietly in his office in the new wing of the Natural History Museum in Rotterdam, the Netherlands, when there was an unusually loud bang one floor below. The wing's all-glass facade sometimes took on mirror-like qualities, so there was a regular supply of birds colliding with the glass. In this case, the collision was from a drake mallard duck ( Anas platyrhynchos ) lying dead on its belly in the sand.

Things took an unusual turn when Moeliker spotted a second, living male mallard nearby, which began pecking at the back of the dead duck's head. After a couple of minutes, the living duck "mounted the corpse and started to copulate, with great force," Moeliker recalled, only stopping for a couple of short breaks. The ornithologist managed to snap some photos of this odd behavior before intervening and collecting the dead duck specimen–over the noisy objections of its living "mate." It was the first documented case of homosexual necrophilia in the species.

(a) Moeliker's office in new north wing of the Natural History of Rotterdam in 1997. (b) Where the duck hit the glass facade. (c) Where Moeliker observed the "homosexual necrophilia." (credit: Christian Richters)

Moeliker published his findings in a 2001 paper that would eventually snag him the 2003 Ig Nobel Prize in Biology . It also inspired the annual " Dead Duck Day " celebration, held at the very spot the unfortunate duck perished, marked by a memorial plaque. The brief commemorative ceremony—which also acknowledges "the billions of other birds that die(d) from colliding with glass buildings and challenges people to find solutions to this global problem," per Moeliker —is typically followed by a six-course duck dinner at a local Chinese restaurant called Tai Wu . The event is co-organized by the museum and the European Bureau of Improbable Research.

Enlarge / A digital reconstruction of a humpback whale engaged in trap feeding. (credit: John McCarthy, Flinders University)

About 10 years ago, marine biologists witnessed two different species of whales in different geographic locations engaged in a novel feeding strategy.  The whales would position themselves at the water's surface and stay motionless with their mouths wide open. Fish would swim into their mouths, and the whales would snap their jaws and swallow. It's been dubbed trap feeding, or tread-water feeding. A clip of whales engaged in trap feeding even went viral on Instagram in 2021.

Yet this feeding strategy might not be as recent as scientists initially thought. Researchers at Flinders University in Australia have found striking descriptions of what sounds a lot like trap feeding in Old Norse descriptions of the behavior of a sea creature called the hafgufa , according to a new paper published in the journal Marine Mammal Science. That creature, in turn, can be traced back to medieval bestiaries and a type of whale called aspidochelone , first mentioned in a 2nd century CE Alexandrian manuscript called the Physiologus .

“It’s exciting because the question of how long whales have used this technique is key to understanding a range of behavioral and even evolutionary questions," said co-author Erin Sebo , a medievalist at Flinders University. "Marine biologists had assumed there was no way of recovering this data but, using medieval manuscripts, we’ve been able to answer some of their questions."

Enlarge / Kittens engage more frequently in reciprocal wrestling ("play-fighting") compared to adult cats, a new study found. (credit: Getty Images)

Anyone with more than one cat in the house knows that the occasional spat or outright cat fight is going to happen. But sometimes it can be tricky to determine whether cats are fighting or just playing rough, because the interaction could feature trademark behaviors of both, according to a recent paper published in the journal Scientific Reports. It's even more challenging to tell whether the fight is just a squabble or a sign that the cats simply can't get along, thereby forcing hard decisions about how to separate the cats—or even whether it's possible to keep the cat(s) in question.

In 2021, co-author Noema Gajdoš‑Kmecová, a veterinarian with the University of Veterinary Medicine and Pharmacy in Košice, Slovakia, and several colleagues published a review paper proposing the development of a common terminology and more of a "psychobiological" approach to the study of cat behavior—particularly when it comes to play behavior. Past studies had focused on a cat's play activity, such as whether it was playing with a toy or another cat. But such observation yields little insight into the function of such play and, by extension, a cat's motives or emotional state.

"When one cat treats another as an object or prey, such activity relates to the former cat seeking to learn about its own skills in relation to manipulating its physical environment (prey are not considered part of the complex social relationships and thus social environment of an individual)," they wrote in that paper. "However, when interaction between cats is reciprocal it may function to facilitate social learning and may be best described as mutual social play." Because such interactions are dynamic, they argued that any functional classification system must be flexible enough to account for such nuances.

Enlarge (credit: Robert Trevis-Smith )

It's pretty easy to link humans' intelligence to our success as a species. Things like agriculture, building cities, and surviving in harsh environments require a large collection of mental skills, from good memory to the ability to communicate and work together. But it's often less clear what role intelligence plays in species with less obvious mental capabilities. In many cases, it's hard to even measure mental capacities; in other cases, it's hard to guess which capacities might improve survival.

A new study looks at a bird species that doesn't have much of a reputation for braininess: the pheasant. But the researchers behind the study find that pheasants have substantial differences in spatial thinking, and some aspects of that spatial capacity make a difference when the birds are released into the wild. Those birds that do well with navigating a complex maze adopted a larger home territory and did better at avoiding being eaten. And, almost as an accident, the study finds that the birds tend to get eaten more often when they wander out of familiar territory.

Can’t outfox the foxes

Parrots and corvids have reputations as the brainiacs of the bird world. Pheasants, not so much. But they do have advantages for the study of mental abilities. They're easy to raise in captivity, where they can be given various tests, and will adjust easily if released into the wild. They're also big enough that it's easy to attach tracking devices to see what they're doing after they've been released.

Enlarge / This bee seems to having a grand old time rolling this colored wooden ball. (credit: Samadi Galpayage)

There's rarely time to write about every cool science-y story that comes our way. So this year, we're once again running a special Twelve Days of Christmas series of posts, highlighting one science story that fell through the cracks in 2020, each day from December 25 through January 5. Today: Scientists captured bees rolling wooden balls, solely for fun, on video, providing additional evidence that bees might experience positive "feelings."

Many animals are known to engage in play—usually large-brained mammals (like humans) and birds. Now scientists think they have observed genuine play behavior in bees, which were filmed rolling small colored wooden balls, according to an October paper published in the journal Animal Behavior.

“This research provides a strong indication that insect minds are far more sophisticated than we might imagine," said co-author Lars Chittka of Queen Mary University of London and author of a recent book, The Mind of a Bee . "There are lots of animals who play just for the purposes of enjoyment, but most examples come from young mammals and birds."

Enlarge / A brown bear with two cubs looks out of its den in the woods under a large rock in winter. (credit: Byrdyak | Getty)

Every spring, as days in the north stretch longer and melting snow trickles into streams, drowsy animals ranging from grizzlies to ground squirrels start to rally from hibernation. It’s tempting to say that that they are “waking up,” but hibernation is more complicated and mysterious than a simple long sleep : Any animal that can spend months underground without eating or drinking and still emerge ready to face the world has clearly mastered an amazing trick of biology.

The roster of animals that hibernate includes all manner of rodents, some amphibians and even a few primates (several species of dwarf lemurs), but bears are literally the biggest hibernators of them all. Adult grizzly and black bears weigh as much as American football players, or more, with the energy and curiosity of preschoolers, but they have no trouble hunkering down for months at time. The choreography that goes into shutting down a creature this big defies easy explanation, says Elena Gracheva, a neurophysiologist at Yale University in New Haven, Connecticut. “Hibernation is so complex it requires adaptations at multiple levels,” she says.

Bear hibernation offers important insights into the workings of large mammals, especially us, explains Gracheva, who coauthored an exploration of the physiology of hibernation in the 2020 Annual Review of Cell and Developmental Biology . A better understanding of the process could potentially change our approach to a wide range of human conditions, including stroke, osteoporosis, Parkinson’s disease and Alzheimer’s (see sidebar).