Morphological and demographic characteristics of the grey hamster (Nothocricetulus migratorius) across lowland and foothill landscapes of the South Caucasus
This study analyzes morphological and demographic variations of the grey hamster (*Nothocricetulus migratorius*) across lowland and foothill landscapes in the South Caucasus using extensive long-term trapping data, revealing significant spatial, temporal, and morphometric differences between populations in Nagorno-Karabakh and Armenia.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Small mammals are the quiet engine rooms of the land. They chew through seeds, turn the soil with their burrows, and serve as a vital food source for birds, foxes, and snakes. Because they live such short lives and reproduce quickly, their numbers can swing wildly from year to year, rising and falling with the weather, the harvest, and the presence of predators. Watching these populations over time is like watching the pulse of an ecosystem; if the pulse slows down or skips a beat, it often signals a deeper change in the environment. One such creature, the grey hamster, is a small rodent that has lived across vast stretches of Eurasia for thousands of years. It is a hardy animal, comfortable in dry steppes, farm fields, and even the edges of human settlements. Yet, despite its wide range, scientists know surprisingly little about how its numbers change over decades or how its body shape might differ depending on where it lives.
For a quarter of a century, researchers have been quietly tracking these hamsters in the rugged landscapes of the South Caucasus. A team of scientists, working across the lowlands and foothills of the Martuni region in Nagorno-Karabakh, set out to understand the long-term story of this species. They did not just count how many animals they found; they also measured their bodies and looked at the mix of ages and sexes in the groups they caught. By combining decades of field notes with fresh data from nearby Armenia, they built a detailed picture of how this common rodent adapts to different places and times. Their work reveals that while the grey hamster is a single species, it is far from uniform; its population numbers rise and fall in complex patterns, and its physical form shifts in surprising ways depending on the specific landscape it calls home.
The study began with a massive amount of fieldwork. Between 1999 and 2023, the team conducted hundreds of surveys in six different locations, ranging from the dry, warm lowlands near 400 meters above sea level to the cooler, wetter foothills rising to 800 meters. They set thousands of live traps, checking them several times a day with bait like carrots and bread soaked in oil. Over the years, they captured nearly 14,000 small mammals in total, of which 1,730 were grey hamsters. To make sure their counts were fair, they only counted the traps that actually worked, ignoring the ones that were broken or empty. This careful method showed that, on average, they caught about 4.5 grey hamsters for every 100 working trap-days.
When the scientists looked at the numbers year by year, a clear story emerged. The population was at its highest at the very beginning of their study, in 1999, when they caught more than six hamsters per 100 trap-days. Over the next two decades, the numbers fluctuated, but there was a noticeable trend: the later years, from 2017 to 2023, consistently showed lower numbers, often dropping below four hamsters per 100 trap-days. This suggests that the population has been experiencing a slow decline or at least a shift to lower numbers in recent years, though the researchers note that they cannot yet say exactly why. It could be changes in farming, the weather, or the availability of food, but the data alone does not point to a single cause.
The landscape itself also played a role. The hamsters were slightly more common in the lowland areas than in the foothills. In the lowlands, the team found about 4.8 hamsters per 100 trap-days, while in the foothills, the number was closer to 4.4. Even within these zones, some specific villages had more hamsters than others. For instance, in the lowland village of Kakavadzor, the population density was the highest recorded, while in the foothill village of Gishi, it was the lowest. This tells us that the broad difference between "lowland" and "foothill" is not the whole story; local conditions in each specific spot matter just as much.
The researchers also took a closer look at the hamsters themselves, measuring their bodies and skulls to see if animals from different places looked different. They found that the hamsters were not all built the same way. Interestingly, the hamsters living in the higher foothills were generally longer in body than those in the lowlands. However, when it came to other features, the pattern flipped. The lowland hamsters had longer tails, longer back feet, and wider skulls than their foothill cousins. This means that the animals did not simply grow bigger or smaller as a whole; instead, different parts of their bodies changed in different directions depending on where they lived.
The team also compared these findings with a small group of hamsters they caught in 2024 and 2025 in the Republic of Armenia, further to the west. These animals were noticeably larger and heavier than the ones from Nagorno-Karabakh. The Armenian hamsters had longer bodies, larger skulls, and weighed more on average. However, because the scientists only spent two years studying the Armenian population, they cannot yet say if this is a permanent difference between the regions or just a temporary snapshot. It is possible that the specific conditions in those two years or the specific habitats chosen for study influenced the results.
Finally, the scientists examined the makeup of the populations, looking at how many males and females there were and how many were young versus old. They found that the balance of sexes and ages varied from place to place. In some locations, there were more young animals, while in others, the adults dominated. This variation is normal for wild animals, as birth rates and survival change with the seasons and the local environment. The fact that these mixes were different across the study sites confirms that each local group of hamsters is responding to its own unique set of circumstances.
This long-term study provides a crucial baseline for understanding the grey hamster in the South Caucasus. It shows that while the species is widespread, its populations are dynamic and sensitive to their environment. The numbers go up and down over time, and the animals themselves change their shape depending on where they live. By standardizing their methods and looking at the data carefully, the researchers have given future scientists a solid starting point. If the hamster numbers continue to drop, or if their bodies change in new ways, this record will help scientists figure out what is happening to the land and the life it supports. For now, the grey hamster remains a resilient but changing part of the region's ecology, its story written in the traps, the measurements, and the shifting numbers of the decades.
Drowning in papers in your field?
Get daily digests of the most novel papers matching your research keywords — with technical summaries, in your language.