Rodent females create extra offspring after smelling odors (chemo-olfactory cues) produced by scared males. Fear of being torn apart and eaten can influence the size of populations. A study showed that exposed small, highly fecund (prolific) species like rat mothers produce families with about 40-60 percent more pups compared to female that were not exposed to frightened males. It was observed that the increase in pups was second-hand evidence that there was predators around and that this was enough to escalate the number of pups. Predators can also scare the living be bejesus out of their prey and the resulting terror alters how they behave and reproduce. Also, these females may sense that their next litter may be their last and need to produce more offspring immediately. Simple physical interaction between the mating pair can regulate the litter size.
gogreenpestcontrol.ca & Exterminators Delta, Ladner Tsawwassen B.C., Randy L. Bilesky BsF CPA RPF
https://www.linkedin.com/pulse/fear-changes-how-rodents-reproduce-randy-bilesky/?published=t
https://www.delta-optimist.com/opinion/blogs/blog-fear-changes-how-rodents-reproduce-1.23506576