May 27, 2009

Study finds rats rarely roam from home

Johns Hopkins scientists in Baltimore say they've found inner city rats, though appearing to roam freely, form distinct neighborhoods which they rarely leave.

The researchers from the university's Bloomberg School of Public Health studied nearly 300 Wild Norway rats -- also called wharf rats, sewer rats or brown rats -- that they trapped from 11 residential areas of the city. They then conducted genetic studies to see how the rats were related.

The scientists found that East Baltimore rats are separated from their unrelated West-side counterparts by a large waterway known as the Jones Falls. Within those areas the scientists discovered rat families form smaller communities of about 11 city blocks. Each community is further divided into neighborhoods that span little more than the length of an average alley.

The scientists said their findings suggest that while rats rarely migrate, neighborhood eradication efforts might backfire by encouraging the rodents to repopulate other areas and further spread disease.

The study appears in the journal Molecular Ecology.