Most obviously different from regular voles are the giant species. Although genetic data shows us that these are voles, in the sense of being offshoots of the vole family tree rather than something distinct, we don't normally refer to them as such in English. Instead, we call them "lemmings" or, in the case of the very largest species, "muskrats". To avoid potential confusion, in more scientific language we would therefore use the taxonomic name when referring to the subfamily as a whole and say that voles, lemmings, and muskrats collectively are "arvicolines".
And then, there are the mole voles.
Mole voles first split away from the rest of their subfamily around 5 million years ago at the dawn of the Pliocene, and form a distinct group within the arvicolines more generally. Their closest relatives are the Balkan snow voles, but two key features distinguish mole voles from their kin.
For one thing, most (but not all) mole vole species lack a Y chromosome. In these species, the males have exactly the same XX karyotype that females do. You might think that the bit of the Y chromosome that determines sex must have moved across to one of the X chromosomes, so that an individual either inherits it (and becomes male) or doesn't (and becomes female). But, nope, it's not there either. Heck, in one species, the karyotype isn't XX, it's just X - the other chromosome has gone altogether, leaving the X unpaired, something that ought to result in Turner's syndrome and reduced fertility but evidently doesn't.
As of 2025, we have no clue as to how sex determination works in these species.
This oddity, however, is not the only thing that sets mole voles apart from more typical voles. There are five recognised species of mole vole, and while not all of them have the weird Y chromosome thing, one feature they do all share is implied in their common name: they're subterranean.
That is to say, mole voles, like moles and mole rats, spend almost their entire lives underground, burrowing through the soil. Unlike true moles, they are vegetarian, eating roots, bulbs, and underground stems, travelling above ground only when they leave home for the first time to establish their own burrow. Their eyes are unusually small, and, while they certainly aren't blind and can probably make out at least blurry outlines of objects, their eyesight is pretty terrible.
On the other hand, the northern mole vole (Ellobius talpinus) at least is a social animal. Family groups average around ten individuals, and they can be twice that size, all sharing the same burrow system. This is usually complex, with multiple sleeping, breeding, and food storage chambers, located an average of 4 metres (12 feet) below the ground. The species lives in Central Asia, reaching southeastern Ukraine in the west, Turkmenistan and far northern Iran in the south, and as far east as the edge of the Altai Mountains in Kazakhstan and southern Siberia. The northern boundary of their range is, perhaps unsurprisingly, determined by where the soil becomes too frozen to dig through in winter.
Each group includes a single dominant female, one or more sexual partners, and a variable number of children and even grandchildren. As in mole rats, this probably allows them to share the effort of constructing and maintaining the burrow. Notably, for example, they often dig in pairs, with one individual taking the lead by gnawing through the soil with their teeth, and another waiting behind to push the excavated soil out of the way and finish the tunnel.
This would all require some form of communication. While solitary animals do often make sounds, vocal communication tends to be more complex in social animals, which typically need to be able to say more than merely "go away" and "I want sex". The fact that these animals live underground also affects the acoustics of the sounds they are going to make, so that these should be different from those made by closely related voles that live above ground.
We already have some studies on the vocal communications of subterranean rodents, including naked mole rats, not-naked mole rats, and a member of the degu family, but only one on a burrowing mole - the Mandarin vole (Lasiopodomys mandarinus), which is not quite as rigorously subterranean as a mole vole.
That changed a few weeks ago, when the same researchers who had looked at the Mandarin voles published their results on the more sociable northern mole vole. In their study, they observed 143 mole voles living in the steppeland near D'yakovka in southern Russia. The test consisted of capturing and measuring the voles, releasing a pair of them in a controlled area where they could encounter one another while digging, and then allowing them to return to their burrows.
The study was able to identify no fewer than eight different kinds of call. Three, of these, which they termed 'wheeks', 'squeaks', and 'squeals' were easily audible to humans. Wheeks, faint, short, calls emitted in a series, were mostly used when encountering other voles in a peaceful situation, and therefore are likely to be contact calls, acknowledging each others' presence. Pairs of animals often 'wheek' to one another at the same time. (They had originally tried to identify contact calls by placing animals in neighbouring cages, but it turns out that when you do this they either hide or are far too busy trying to escape to pay any attention to each other).
That these sounds were quiet supports the idea that they're friendly greetings, where being heard at a distance would not be useful and the animal probably wouldn't want the sound to echo down the tunnel. They are similar to the twitters of mole rats and the cooing of some other social rodents. A study conducted in 2007 on a species of solitary gopher was unable to find anything similar; if you're antisocial, you don't need a sound for "friendly greeting".
Squeaks are louder and longer, and seem to indicate a moderate degree of frustration. Used either alone or in a short series, they most often happened when two animals tried to dig in the same place or had to climb over one another to get where they wanted. Squeals were loud, long calls, indicating that the animal is really uncomfortable - mainly when they were being picked up to be measured.
However, there were also three types of ultrasonic call, beyond the range of human hearing. Some of these, which the researchers termed "variatives" had no clear function, but the more common "upsweeps", where the tone rises to a higher pitch, seem to indicate friendly contact, and perhaps happiness. They were often made when animals nuzzled each other on the nose, and were especially common after they had been released and returned to their home burrow - presumably reuniting with their family after the enforced separation. It may be notable that this sound wouldn't propagate very far down a tunnel, due to its pitch... but it wouldn't need to be if it's a greeting.
"Squeezes" were super high-pitched calls often emitted alongside the squeals, and so presumably indicating much the same degree of discomfort. A "twit" sound that mixes human-audible and ultrasonic tones seemed to be another greeting, perhaps when the animal hadn't fully calmed down after capture. A growly "rasp" that also mixed in ultrasonic components seems to be an alarm call, used when the animals are plugging up a tunnel that has become open to the air potentially allowing a predator to get in.
Much of this fits with what we know from other rodents living in more typical circumstances, although there are unique differences that could either be related to underground living (say, the way that sound propagates through tunnels) or just to the fact that this is a different species. Either way, it's a glimpse into the lives of family-living animals normally hidden 4 metres underground so we wouldn't even know they were there.
[Photo by Alexandra Kaganova, from Wikimedia Commons.]
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