How many baby mice are born at one time? - briefly
A typical litter comprises «5–6» newborns, though counts may vary from three to twelve in larger litters. Gestation lasts roughly 19–21 days, after which the altricial young are born.
How many baby mice are born at one time? - in detail
The common house mouse typically produces litters of 4 to 12 offspring, with 6 to 8 being the most frequent count. Litter size can reach 13 in exceptional cases, but numbers below 4 are rare under optimal conditions.
Factors that modify the number of newborns include:
- maternal age (young and very old females tend to have smaller litters);
- nutritional status (adequate protein and energy increase litter size);
- genetic line (selected laboratory strains may yield larger or smaller litters);
- seasonal cues (longer daylight periods often correlate with higher reproductive output);
- health of the mother (parasitic load or disease reduces offspring number).
Wild species display comparable ranges. The meadow mouse (Apodemus sylvaticus) generally yields 3 to 7 young, while the deer mouse (Peromyscus maniculatus) averages 5 to 9 per birth. Extreme environments can shift these figures downward.
Gestation lasts 19 to 21 days, after which neonates weigh 1 to 2 grams and are altricial: eyes remain closed, fur is sparse, and thermoregulation is undeveloped. Pups cling to the mother’s nipples and receive nourishment exclusively from milk until the weaning period at 3 to 4 weeks of age.
Survival to weaning averages 60 % to 80 % in stable laboratory settings; in the wild, predation, competition, and environmental stress lower this proportion. Litters delivered in secure nests with abundant food achieve the highest conversion of births to independent juveniles.