In wildlife studies, individual animals are usually uniquely marked to collect data related to population ecology and behavior such as social structure, migration and dispersion, growth and age identification, seasonal fluctuation of physical features, reproductive patterns, life-history strategy, nesting territory and home range. Wild animals are mainly superficially marked with ear tags, ear-rings, neck collars, cut toes, foot bands, hair shearing, clipped ears, colored hair, brands, and tattoos. Using cut toes, colored hair and ear tags to mark individuals are normal techniques in population ecology studies on small rodents. However, all of these marking methods have various disadvantages. For example, clipped ears and cut toes physically harm animals and may affect their normal behavior as well as physiological condition. Because ear-rings are easily lost and colored hair lasts only a short time, these two methods are not suitable for long-term ecological research. Furthermore, all regular marking methods are difficult to use for marking individuals in a large population. These obvious disadvantages may potentially affect the reliability of results obtained.
A passive integrated transponder (PIT) is part of an electronic marking system based on radio frequency identification allowing each marked animal to bear a unique international code. The PIT tag remains dormant until activated at close-range by a handheld reader, which generates an electromagnetic field. PIT tags are small and light, giving them an advantage over traditional marking methods in that they can be implanted inside animal bodies and have a minimal affect the physiology and behavior of marked animals. PIT tags were first used in measuring fish movement in 1983. Since then, PIT tags have been widely applied in animal research among invertebrates, amphibians, reptiles, birds and mammals and are popular worldwide especially for use in zoos, aquiculture and animal trade. Nevertheless, the application of PIT tags is restricted to a few aquatic animals in China.
We adopted PIT tags and mark-recapture techniques to investigate the population dynamics of Siberian chipmunks (Eutamias sibiricus) during five time periods from October, 2011 to June, 2012 in Liangshui National Nature Reserve in Heilongjiang Province, China. A total of one hundred and forty chipmunks were marked, of which eighty-six were recaptured at least once. Seventy-two chipmunks were marked in autumn, 2011, thirty-eight of which were recaptured in spring, 2012. The injection wounds of all recaptured chipmunks had healed well and they exhibited no significant decrease in body weight. We estimated the dynamics of the chipmunk population based on mark-recapture data. The results showed that the average population density of chipmunks in the Korean pine forests of the Reserve was 8.91±2.76 per hectare in autumn, 2011 and 6.14±1.29 per hectare in spring, 2012. After the analysis of individual recapture records, we found that the maximum movement distance of studied chipmunks was not significantly different in autumn ((65±8) m) and in spring ((67±4) m). Chipmunks exhibited a clumped distribution pattern in autumn and uniform pattern in spring. These results indicated that PIT tags provide an ideal internal safe and reliable electronic marking system because they allow rapid and accurate identification of individuals when collecting data, last a long time when worn inside animal bodies, are less harmful to marked animals than other marking techniques, are rarely lost and are reusable. In summary, PIT tags allow the identification of individual small mammals, are mainly useful in wildlife ecology, and are especially suitable for population ecology.