"Rodent mothers produce more offspring after smelling odors produced by frightened males. This is reported by a team of biologists from Finland and the Netherlands and bring new information the proximate and ultimate explanations of small mammal behavioral responses." Source: Phys.org.
"Fear of being eaten has the power to shape populations and drive evolution. The effect the authors report is large: exposed mothers produce litters with about fifty percent more pups compared to unexposed control mothers."
Comment: If the rat population can grow so explosively in places like India where they're venerated, I hate to think how quickly they reproduce when living in a state of fear. Rats, of course, are considered to be vermin in the West but they're actually nothing to be afraid of according to the noted English rat expert, James Herbert.