Study Finds Urban Mice and Rats Adapting to Traps and Poisons

Researchers collected DNA samples from 300 rodents across dense urban areas in New Jersey, Pennsylvania, Washington DC and New York. They identified different adaptations between the two species.

Seventy percent of the house mice sampled carried a genetic mutation that made anticoagulant poisons ineffective. The rodents can consume the poison and continue normal activity. Mice developed this tolerance after repeated exposure to unfamiliar food sources, including poison baits, over many years.

Norway rats showed no comparable genetic change but demonstrated learned avoidance of physical traps. Video recordings documented rats making hundreds of approaches before touching snap traps or sticky traps. One rat population studied in the Bronx required up to a week of repeated approaches before any contact with traps occurred.

Continued use of rodenticides could affect non-target wildlife that consume poisoned rodents. Studies have detected rodenticide residues in animals that feed on roadkill. The researchers stated that cities may need to explore non-chemical approaches focused on prevention and sanitation to limit rodent populations.