This section is 1.50 min long, with soundtrack (see also "SILENT CLIPS")

Chapter size: 18 MB (.mpg) or 3 MB (.mov).

Topics and Behaviours covered: birth, multiple paternity, parental care, competition, infanticide (see commentary below).

Chapter commentary:
(numbers in bold refer to behaviours also shown in the silent clips)

Three weeks later, 10 pups are born (1). Litter size in lab rats is generally more than their wild cousins. But like them, the litter can be fathered by different males.

Females make attentive mothers as virtually no care is provided by the males. Pups are born blind and hairless and will be dependent on the mother for several weeks. They are at the mercy of predators, and that includes other members of the colony...

(2) Infanticide, though not frequent, is widespread amongst mammals. Many instances of infanticide are attempts to limit competition. In some rodents females may kill the pups of other females, but the real danger are the males who, profiting of the female’s brief absence, may kill some or all the pups.

This infanticidal male is probably not the father of this litter as males are less likely to attack the litter of females with whom they have mated. However cruel it may seem, it makes biological sense of course, as these pups will never compete with his offspring. Perhaps it is because of this biological equivalent of a protection racket that females accept, indeed solicit, mating with several males. In the mating frenzy, the males cannot be sure that at least some of the pups are not theirs. The ruse appears to work, as this was the only incident that we observed during the filming.