Rats are homely and have a fairly small radius of action.
Read aloud Rats in big cities remain true to their ancestral territory and move only in exceptional cases farther than several hundred meters away. This is what US researchers found out in genetic studies of urban rodents in Baltimore. The typical radius of action of a rat corresponds to about a block, as it is determined by the checkerboard-like layout of the streets of the city. There are about eleven blocks to a family's territory, with larger areas being delineated by obstacles such as rivers, according to researchers around Lynne Gardner-Santana at Johns Hopkins University in Baltimore. In their study, the scientists studied brown rats as they inhabit thousands of major cities around the world. The researchers captured around 300 rats in 11 different districts of Baltimore, took gene samples and determined the relationships of the captive animals. From this genetic map resulted in the surprisingly large fidelity of the animals: As a rule, the wandering rats within the block in which they are born. Only a small percentage moves farther than 400 meters away. Only in exceptional cases, there are migratory movements that lead the animals once across the city, the researchers found out.

The reason for this site loyalty lies in the highly developed social system of rats with a pronounced family structure, which is also defended to the outside, explain the scientists. On the other hand, there could be greater migration if the rats in one area are nearly wiped out, leaving neighbors with no danger of spreading. Therefore, programs to control rats should always take into account possible migratory movements of neighboring populations, the researchers write.

Lynne Gardner-Santana (Johns Hopkins University, Baltimore) et al .: Molecular Ecology, doi: 10.1111 / j.1365-294X.2009.04232.x ddp / science.de? Ulrich Dewald

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