Research into the hunting behavior in members of the Cricetidae family offers an opportunity to reveal what changes in the predatory behavioral sequences occur when a rodent species shifts from an omnivorous to a predatory lifestyle. The study tests the following hypotheses: are there phylogenetic differences in the divergence of species’ predatory lifestyles in hamsters or do ecological factors lead to shaping their hunting behavior? We applied the data compression approach for performing comparative analysis of hunting patterns as biological “texts.” The study presents a comparative analysis of hunting behaviors in five Cricetinae species, focusing on the new data obtained for the desert hamster Phodopus roborovskii whose behavior has never been studied before. The hunting behavior of P. roborovskii appeared to be the most variable one. In contrast, behavioral sequences in P. campbelli and Allocricetulus curtatus display more significant order and predictability of behavior during hunting. Optional hunting behavior in the most ancient species P. roborovskii displayed similarities with obligate patterns in “young” Allocricetulus species. It thus turned out to be the most advanced hunter among members of the Phodopus genus. Differences in hunting sequences among Phodopus representatives suggest that the hunting behavior of these species, despite its optional mode, was subject to selection during species splitting within the genus. These results did not reveal the role played by phylogenetic differences in the divergence of species’ predatory lifestyles. They suggested that ecological conditions are the main factors in speciation of the hunting behavior in hamsters.

The development of cognitive ethology and new experimental methods for the study of animal intelligence has led to an underestimation of the role of innate stereotypes in the behavioral repertoire. Researchers tend to see cognitive phenomena in animal activity. On the example of ants and rodents, using an experimental model of interaction with prey, we identified relatively flexible fragments of innate stereotypes prone to recombination or loss. We propose that variability of individual fragments of stereotypes underlies the formation of species-specific hunting behavior. The combination of innate fragmentation of behavioral stereotypes and simple forms of social learning may lead to certain behavioral traditions within communities and populations. This review presents the results of research team’s studies and considers the prospects of the proposed direction of studies based on a detailed analysis of behavioral stereotypes.

Predatory hunting is a complex species-typical behaviour involving different skills, some of which may include learning. This research aims to distinguish between rigid and flexible parts in live-insect hunting behaviour in nine herbivorous and granivorous rodent species, and to find out whether there is room for cognition in this activity. In laboratory experiments, all species studied manifest skilful attacks towards insects in a manner that is typical for specialised predators chasing a fleeing prey. Voles demonstrate a “core” and somewhat primitive scheme of a hunting pattern: approaching a potential victim, biting it, and then seizing and handling. Hamsters display the tendency to start their attacks by actions with paws, but they can achieve success only using teeth as well. Gerbils can successfully use both paws and teeth to start the attack, which brings their hunting behaviour closer to that of specialised rodent predators. We revealed variability in the display of hunting in different species, methods of seizing the prey, and the number of attempts to attack an insect before catching it. We found specific flexible fragments within the “bite–grasp–handle” bouts that can be precursors for adaptive phenotypic variations and include some cognitive attributes. We hypothesise that the divergence and specialisation of predatory behaviour in rodents can be based on the natural fragmentation of the original hunting patterns, that is, on the loss or recombination of particular behavioural elements. We consider a possible link between the fragmentation of hunting behaviour and social learning in different classes of animals and conjecture an intriguing correlation between predatory activity, cognitive skills and personal traits in rodents.

In laboratory experiments, purposeful predatory inter-relations with moving insects have been revealed and described in three species of herbivorous voles: the East European vole, the narrow-headed vole, and the Tuva silver vole. The appearance of the full hunting stereotype in these species does not require preliminary experience, which indicates its innate nature. The hunting behaviour of the Tuva silver vole differed from that of the East European vole and narrow-headed vole, which probably reflects the phylogenetic relationships between these species.

The development of cognitive ethology and new experimental methods of studying animal intelligence has led to an underestimation of the role of innate stereotypes in the behavioral repertoire. Researchers tend to see cognitive phenomena in animal actions, such as the formation of cultural traditions in communities. On the example of ants and rodents, using an experimental model of interaction with prey, we identified relatively flexible fragments of innate stereotypes prone to recombination or loss. We suggest that the variability of individual fragments of stereotypes underlies the formation of species-specific hunting behavior. The combination of innate fragmentation of behavioral stereotypes and simple forms of social learning may lead to certain behavioral traditions within communities and populations. The review presents the results of the research team's studies and considers the prospects of the proposed direction of investigations, based on a detailed analysis of behavioral stereotypes.

In laboratory experiments, purposeful inter-relations with moving insects in the “predator–prey” manner have been revealed and described in two species of herbivorous mountain voles: the Tuva vole and the flat-headed vole. The patterns of the hunting behavior are similar in these species. The appearance of the full hunting stereotype in mountain voles does not require preliminary experience and does not improve, which indicates its innate nature. Unlike the rodent species studied earlier, mountain voles demonstrate “storing” behavioral patterns when operating with live prey. According to the characteristics of the interactions with prey, mountain voles are among the most successful and effective hunters for moving insects. Regarding the hunting tactics and the manners of their manipulations with prey, mountain voles are similar to the most “predatory” of omnivorous hamsters, Eversmann’s hamsters, but differ from them in an optional manifestation of the hunting stereotype. The frequency of occurrence of the stereotype and the success of hunting in mountain voles are twice as high as in the previously studied herbivorous narrow-head vole. Characteristics of a hunting behavior so unexpected in herbivorous rodents were revealed in mountain voles for the first time. The expansion of the diet due to the hunt for insects can be attributed to dwelling in arid places with a deficit of plant food resources.

In three rodent species with different types of nutrition, a targeted “predator–prey” type interaction with mobile prey was revealed for the first time and described in detail. The granivorous striped field mouse, herbivorous narrow-skulled vole, and omnivorous Campbell’s dwarf hamster have an equally efficient, stereotypical hunting behavior that is in many ways similar to the behavior of the common shrew (specialized insectivorous species). At the same time, the hunting rate in rodents is lower than in insectivores. Unlike insectivorous species, rodents have a stereotypical hunting behavior that is manifested facultatively (completely, but not in all individuals). The portion of “hunters” in narrow-skulled voles is two times lower than that in striped field mice. The tactics of prey killing vary in different species: striped field mice, narrow-skulled voles, and shrews immobilize an insect with a series of quick bites; Campbell’s dwarf hamsters bite off limbs of the prey, which is apparently a manifestation of a more specialized hunting behavior. The nature of hunting attacks is different: first capturing the prey by teeth, rodents move to a capture with paws, while shrews use only teeth, which indicates a relative primitiveness of their predatory behavior. Campbell’s dwarf hamsters can start the attack with a capture using both teeth and paws, which characterizes their hunting behavior as the most evolutionarily advanced among the studied species. The stereotypes of hunting behavior in all three rodent species are manifested according to the principle “all at once” and are not affected by experience. The hunting behavior of rodents can be considered an evolutionarily stable strategy that supports the ability of populations to hunt moving insects in order to expand the spectrum of food resources.

One of the main problems in comparative studying animal behavior is searching for an adequate mathematical method for evaluating the similarities and differences between behavioral patterns. This study aims to propose a new tool to evaluate ethological differences between species. We developed the new compression-based method for the homogeneity testing and classification to investigate hunting behavior of small mammals. A distinction of this approach is that it belongs to the framework of mathematical statistics and allows one to compare the structural characteristics of any texts in pairwise comparisons. To validate a new method, we compared the hunting behaviors of different species of small mammals as ethological "texts." To do this, we coded behavioral elements with different letters. We then tested the hypothesis whether the behavioral sequences of different species as "texts" are generated either by a single source or by different ones. Based on association coefficients obtained from pairwise comparisons, we built a new classification of types of hunting behaviors, which brought a unique insight into how particular elements of hunting behavior in rodents changed and evolved. We suggest the compression-based method for homogeneity testing as a relevant tool for behavioral and evolutionary analysis.

Using the data-compression method we revealed a similarity between hunting behaviors of the common shrew, which is insectivorous, and several rodent species with different types of diet. Seven rodent species studied displayed succinct, highly predictable hunting stereotypes, in which it was easy for the data compressor to find regularities. The generalist Norway rat, with its changeable manipulation of prey and less predictable transitions between stereotype elements, significantly differs from other species. The levels of complexities of hunting stereotypes in young and adult rats are similar, and both groups had no prior experience with the prey, so one can assume that it is not learning, but rather the specificity of the organization of the stereotype that is responsible for the nature of the hunting behavior in rats. We speculate that rodents possess different types of hunting behaviors, one of which is based on a succinct insectivorous standard, and another type, perhaps characteristic of generalists, which is less ordered and is characterized by poorly predictable transitions between elements. We suggest that the data-compression method may well be more broadly applicable to behavioral analysis.

Investigations of the mechanisms of the spatial-behavioral interaction of members of diverse and significant guilds such as red wood ants and small mammals have been started only recently, and many questions remain obscure. We have investigated interrelations between red wood ants Formica aquilonia Yarr and the common vole Microtus arvalis Pallas, the bank vole Myodes glareolus Schreber, and the pygmy wood mouse Sylvaemus uralensis Pallas in laboratory experiments. We first describe the defensive behavior of rodents and reveal a stereotype of the hunting behavior of the common vole towards dangerous insects. In all three rodent species, defensive behavior increases with an increase in the number of ants used in the tests, which corresponds to simulated natural situations with gradations of the dynamic density of insects. We speculate about the relationship between the defensive and hunting behavior of rodents towards red wood ants.

We revealed and analysed patterns of hunting behaviour in three rodent species (the granivorous striped field mouse, the herbivorous narrow-headed vole, and the omnivorous Campbell's dwarf hamster) towards active insects in comparison with the insectivorous common shrew. Unlike shrews, rodents display facultative hunting behaviour, that is, not all specimens can hunt, although the hunting patterns are fully complete in other members of the groups. For instance, the proportion of "hunters" within the group of narrow-headed voles is barely half of that displayed by striped field mice. The rate, effectiveness and features of hunting behaviour are similar in the insectivorous species and the rodent species with different diets. The manner of killing the prey differs between species: mice, voles and shrews apply series of fast bites to kill the insect, whereas hamsters bite its legs off, which can be considered as more specialised hunting pattern. The manner of the attack also varies across species: rodents first grasp the prey with teeth and then move on to grabbing it with the paws, whereas shrews use teeth only, and this can be considered a relatively primitive predatory behaviour. Campbell's dwarf hamster can start the attack both from grasping the prey either with teeth or with paws, and this can be evaluated as the most evolutionary progressive among the species investigated. The main features of hunting behaviour, as well as the ratio of the elements in the patterns, display 'all and immediately' in all three rodent species, and they are not affected by experience. One can consider the hunting behaviour evolutionarily stable strategy of rodents, which allows populations using predation on active insects to expand their feeding resources.

In laboratory experiments we investigate hunting behavior towards insects in Phodopus sungorus (Pallas 1773), P. сampbelli (Thomas 1905), Allocricetulus eversmanni (Brandt 1859), and A. curtatus (Allen 1925). In these species purposeful inter-relations with insects in the predator–prey manner have been revealed and described in details. In all species investigated, the patterns of hunting behavior are comparable with those of specialized predator hamsters. In a quarter of all cases, hamsters start attacks by seizing the prey with their paws, which is considering more evolutionary progressive than capturing with their teeth. The Djungarian hamster P. sungorus demonstrates the simplest pattern of hunting, whereas in other species some features of specialization have been revealed, such as different forms of manipulation activity. A. curtatus displays the swiftest and most effective attacks towards prey. We speculate that the obligatory innate patterns of hunting in both Allocricetulus species are connected with more specialized predatory behavior of members of this more evolutionary young group as compared to members of the genus Phodopus, with their optional hunting patterns which need experience to be completed.

We compare predatory behaviour towards a mobile insect in three species of small mammals: the granivorous striped field mouse, the insectivorous common shrew and the Norway rat (a generalist). The striped field mouse displays a surprisingly efficient hunting stereotype. We apply the data compression method (Ryabko et al. Theory Comput Syst 52:133–147, 2013) to compare the complexity of hunting behavioural patterns and to evaluate the flexibility of stereotypes and their succinctness. Norway rats demonstrated the highest level of complexity of hunting behaviour, with the highest proportion of ‘auxiliary’ and ‘noise’ elements and relatively low proportion of ‘key’ elements in their behaviours. The predominance of ‘key’ elements resulted in similarly low levels of complexity of hunting stereotypes in striped field mice and shrews. The similarity between hunting stereotypes of the insectivorous shrew and the granivorous striped field mouse enables us to argue about evolutionary roots of hunting behaviour in small mammals. We show that this method is a useful tool for comparing ethograms as ‘biological texts’.

Being a great source of nutrition for many rodent species, invertebrates, including insects, have been under–estimated before as an alternative feeding resource. Reactions towards mobile insects (speckled cockroach Nauphoeta cinerea Olivier, 1789) were experimentally investigated in three rodent species with different types of diet, such as omnivorous, granivorous and herbivorous, in comparison with the insectivorous common shrew. In all investigated rodent species highly stereotypical hunting behavior was revealed, comparable with that of a common shrew, which is known as a specialized predator. This enables us to suggest that certain proportion of carriers of hunting stereotypes towards live insects is maintained within populations of rodents, thus enriching their diet.