A unique scientific and experimental facility for studying cats operates in Chernogolovka, near Moscow. Sergei Valerievich Naidenko, Doctor of Biological Sciences, Corresponding Member of the Russian Academy of Sciences, and Director of the A.N. Severtsov Institute of Ecology and Evolution at the Russian Academy of Sciences, spoke with Nauka i Zhizn (Science and Life) about the Far Eastern wildcat's pre-winter fattening, why Amur tigers have once again begun to roam along roadsides, and what lynxes hide about their childhood.
— Sergey Valerievich, why cats?
— As for me, I've loved cats since childhood; they inspired my scientific specialization. The cat is the perfect predator, standing at the top of the food chain, the pinnacle of evolution. I admire their grace, adaptability, intelligence, and cleanliness. And this doesn't depend on the species — a domestic cat, a tiny black-footed cat, or a tiger, the largest of all cats.
— How did you end up conducting cat research in Chernogolovka, a science city populated primarily by physicists?
— Our institute's research and experimental base was built there back in 1975. We were looking for a location close to Moscow, but in relatively wild, untouched conditions, to study the behavior and communication of wild animals. Enclosures were built right in the forest, four kilometers from the city proper, and the necessary conditions were created. Initially, the range of species was much larger. But now, mostly small cats remain.
— What species do you currently have there?
— We have a population of lynxes, eleven adult animals. We also have other cat species: domestic feral cats, the Far Eastern wildcat, caracals, servals, Pallas's cats, ocelots, and haus cats. But lynxes are our main "contingent." They're currently in their mating season, and they scream very loudly during this time (the interview took place in March 2026 – editor's note). A human can hear this scream from up to two kilometers away. It's clear that a lynx, whose hearing is much more acute - it can hear a hare gnawing on a twig from up to two hundred meters away - can hear the scream of a fellow lynx from at least five kilometers away. From this, it gleans certain information about that fellow lynx. We conducted a study in enclosures. It turned out that the pitch of a male's scream clearly correlates with testosterone levels, just like in humans. The higher the testosterone, the lower and bassier the voice. I'm pretty sure a female lynx can tell how good a male is from several kilometers away.
— Is it the same for humans? The lower your voice, the more women will flock to you?
— Just try shouting in a lower voice than you're naturally inclined to! But if we're talking about men's voices, it's no coincidence that the change in boys' voices happens with puberty, when the voice becomes rougher, more "masculine." This is, again, due to the higher concentration of testosterone, which begins to be produced in the body in large quantities at this time.
— What kind of research do you conduct?
— Almost all felines are secretive, with the exception of those cats that live in open spaces, like the cheetah. Observing their behavior in the wild is extremely difficult, practically impossible. I spent 15 years studying Amur tigers in the forest, and during that time, I never saw one in the wild. And thank goodness, I guess. Therefore, working with cats in captivity gives us the opportunity to observe aspects of behavior that we don't see in the wild.
— We work with relatively non-invasive or minimally invasive methods, trying to avoid traumatizing the animals. The most invasive procedures are collecting blood and sperm from males to assess their quality and develop cryopreservation methods. We also conducted an experiment where we implanted subcutaneous temperature sensors and removed them after two to three months of research. Our animals are quite valuable and highly organized, and we need them to feel well. Therefore, we are primarily interested in the ontogenesis of behavior, its development with changes in body weight, hormonal levels, and immune status throughout the year, depending on the animals' breeding cycles and stress levels.
— What causes their stress? Here are the lynxes sitting in their enclosure, all quiet and calm. What kind of stress could there be?
— A variety of things. Selye's definition of stress (Hans Selye, 1907-1982, Canadian endocrinologist – editor's note) is an adaptive response of the body to a change in the environment, through which the animal tries to adjust. From this perspective, a stress response can be caused by changes in temperature, light conditions, or the presence of other individuals. In general, stress is what allows an animal to survive. Of course, reactions to stress can vary. There are a number of variations in the body's response to the same stimulus. Some darted away from a loud sound, while others became wary and began to observe what was happening. Natural selection gradually begins to eliminate some of these variations. If someone stood still for too long, they were eaten. And when you look at the population a few years later, you'll find that as soon as a loud crunch is heard, everyone runs. This is clearly evident in the tigers in the Far East. When we started working there in 2008, we traveled extensively throughout the reserve, and tigers were always nearby. A tiger followed me through the forest for four hours at night. It was, I'll tell you, a dubious pleasure.
— How did you know it was nearby?
— The dog was afraid, and later we found a tiger`s tracks following our own. We've been in situations many times where you're driving down the road and you see tiger tracks coming your way, and it's clear it's gone into the forest. An hour and a half later, you come back and the tiger's tracks follow the car's tracks. But what's interesting is that we always heard stories from colleagues about driving through the reserve in the 1980s and seeing a tiger standing there, not hiding.
— Why wasn't it afraid?
— Because back then it wasn`t a target of poaching; it was well protected. As soon as they started shooting tigers in the 1990s, their behavior changed dramatically. Anyone who stood still died. That was the wrong behavior. As a result, the tigers lay down; we've often seen tigers lying down by the road, letting a car pass. In the last four or five years, the tigers have started standing again. They're better protected, and they're becoming a little bolder, even going into villages.
— But let's return to the topic of Chernogolovka. What research results were unexpected for you?
— For example, we conducted a series of experiments in which we tried to see how the presence of a larger predator affects the health of nearby animals. We examined this on the caracal and the Far Eastern wildcat. The caracal is a significantly larger cat, almost the same size as the lynx. It turned out that there is a correlation, it is indeed negative, but it's much stronger for the caracal, as a potential competitor for the lynx, than for the Far Eastern wildcat, as the lynx's potential prey. What also surprised us were the significant changes in the Far Eastern wildcat's body weight depending on the time of year.
— What do you mean?
— Many have heard about the Pallas's cat's winter fattening. The Far Eastern wildcat's fattening is much greater than that, percentage-wise. An adult male weighs five and a half kilograms in the summer, and in November at our base, we recorded weights of ten to ten and a half kilograms.
— Is this normal? Or is it obesity?
— This is normal for a Far Eastern wildcat. Unlike a lynx, it's very poorly adapted to moving over snow. It has short paws, very small paw pads, and sinks deeply into the snow. If you startle it into jumping into the center of its enclosure, where the snow is untouched, it simply sinks into the snow and can't get back out.
It can't really wade through deep snow in winter. As a result, it's very difficult for it to hunt in the wild during this period. It's normal for it to wait for a solid crust to form and hunt properly, or to sit in a shelter for several days, up to a week, and not eat anything. This isn't hibernation; it's just sitting and waiting. In this situation, it's clear it needs to prepare well for winter, which is why it gains twice its normal weight in the fall. I always tell girls: imagine losing half your weight for swimming season, then gaining twice your weight again by winter. For a human, this would be extremely dangerous, but for a cat, it’s a survival norm. It's certainly astonishing.
— What else surprised you?
— Perhaps the most unique thing we've described is the phenomenon of intra-litter aggression in lynxes. This is a situation where, at a specific age, approximately 45 to 50 days, one kitten in a litter - and lynxes usually give birth to two or three kittens - attempts to kill another.
— Kill? They're not just playfighting?
— Yes. It happens completely out of the blue; we don't see any reason for it. A pair of kittens are living together, playing peacefully, and then suddenly one, as if on cue, starts trying to kill the other, and the motivation is very strong. Sometimes, you grab a kitten, it barely pays you any attention, you hold it, and it watches the other kitten running around on the other side of the mesh.
— How does the mother behave?
— She tries to break it up. It's better if the mother has previously had this experience. A mother who sees this for the first time is less prepared and extremely worried because the attacked kitten screams loudly. The mother's automatic defense reaction is to rush around and not really know what to do about it. We had a case where one of the kittens died from the mother's grip - she grabbed it too hard.
— Have you managed to figure out the reason for this behavior?
— It's a long story from an evolutionary perspective. First, it's clearly timed to coincide with the transition to meat as the primary food source. Before that, kittens feed exclusively on their mother's milk, and at 40-50 days, they begin to test out meat. In nature, the mother brings meat to the den. It's important to understand that when a mother feeds her kittens, her lactation gradually increases, producing more and more milk. But the kittens also grow and eat more and more. So, at some point, this lactation plateaus - the mother can no longer produce milk, no matter how she's fed. And the milk supply is still low. At this point, the kittens begin to gradually switch to meat. This is clearly visible in their growth rate - it slows. But as soon as they start eating meat, they experience a sharp growth spurt.
— And aggression emerges precisely at this time?
— Yes. The prey the mother brings back is usually small. It might be mice, or more often, a hare. They might not have enough food, so the instinctual competition kicks in.
— Don't other cats have this?
— No, only lynxes. I think it's because most other cats don't produce such large litters. Our domestic cat has an average of four kittens, maybe more. From an evolutionary perspective, it doesn't make sense to kill one when you have four other siblings. The Far Eastern wildcat also has a larger litter, while the ocelot has a single kitten. With the lynx, it's clear: when a kitten wins or kills another in a fight, it grows very rapidly.
It also turns out that lynx milk contains significantly less protein than the milk of the Far Eastern wildcat or the domestic cat. It has a slightly different composition, and therefore, perhaps the hunger problem may be more pronounced in them than in kittens of other species.
— Are you working on preventing this?
— Of course, we're not sadists. It used to go unnoticed when these fights occurred, and we'd only see the aftermath after someone had already died. Now we've learned to separate the litters during these times: we separate the aggressor from the others and place the kittens in adjacent enclosures. Everyone survives.
— And how do the lynxes react to this?
— We move the mother back and forth between halves of the litter at 12-hour intervals, and she feeds them all. Of course, she's worried and tries to bring them together, but what can you do? After about a week, ten days at the most, the aggression usually subsides.
— Humans have cases of morbid jealousy between children, where the older child can even injure the younger one. Do you think this isn't jealousy in lynxes?
— No, it doesn't seem that way. I think it's an evolutionary adaptation for them, aiding in the survival of the fittest. What's really unclear here is the mechanism that activates it. It seems like it happens as if at a flick of a switch, and this switch is incomprehensible to us. I'd like to understand how it works.
— Why are these studies important, and what do they mean for humans?
— If we're talking about aggression, it's important to try to understand the mechanisms of this process and how it's triggered. Fighting is a behavioral trait that clearly impacts survival. By understanding these issues, we can better understand ourselves and learn to manage aggression.
Interviewer: Natalia Leskova