title

A system for determining age groups of rodents based on morphometric skull parameters to assess the demographic structure of populations

author(s)

Igor Polischuk (orcid: 0000-0001-5648-4911)

affiliation

E. F. Falz-Fein Askania-Nova Biosphere Reserve, NAAS of Ukraine (Askania-Nova, Ukraine)

bibliography

Theriologia Ukrainica. 2025. Vol. 30: 127–141.

DOI

language

Ukrainian, with English summary, titles of tables, captures to figs

abstract

The variability in populations of mouse-like rodents was studied by identifying and analysing the proportions of different age groups, assessed according to a number of parameters available from the analysis of osteological materials from pellets of birds of prey, primarily owls. The analysis is based on a series of samples belonging to the species Microtus socialis, Microtus levis, Cricetulus migratorius, and Mus musculus, which are typical inhabitants of the protected steppe. Several systems were analysed in detail, primarily the length of the skull, the upper row of molars and mandible, the degree of development of the crests on the skull and the degree of molar wear (in species with bunodont molars). For comparison, data on specimens obtained by direct trapping and for which morphometric indicators, including body weight, are known were used. Based on these data, and primarily on metric indicators, age groups were identified for each species, ranging from 3 to 12 depending on the species and type of character. On this basis, the dynamics of the age structure of populations of each of the studied species is shown using comparisons of data from different seasons of the year and different years of data collection. Thus, it is shown that the combination of morphometric indicators with the assessment of the condition (wear) of teeth allows expanding the interpretative possibilities of the pellet method in long-term monitoring studies. It is also shown that molar wear in hamsters and mice as a criterion for age assessment does not always coincide with the size group based on the length of the molar rows and mandible, since it depends not only on absolute age but also on trophic conditions. In general, the distribution of rodent cranial remains by size groups, assessed by the length of M13, mandible length and other defined age categories, gives an understanding of the age structure of populations. For a quick assessment of the age structure of the small mammal population, only the lower jaws can be used, if they are laid out in a straight line and their sizes are visually assessed or measured.

keywords

craniometry, molars, age variation, rodents, population dynamics

references

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