Pregnancy in female mice, lasting approximately 19 to 21 days, involves significant physiological and behavioral adaptations. These changes support the development of offspring and prepare for their arrival, ensuring the continuation of the species.
Early Gestation Behavioral Shifts
Early in gestation, female mice exhibit subtle behavioral shifts. Their activity levels often decrease, particularly during the dark, active phase, contributing to a positive energy balance necessary for pregnancy. These changes can be observed from around days 0.5-6.5 of pregnancy.
As pregnancy progresses, feeding and drinking patterns change. Pregnant mice tend to consume more food, often eating larger meals, especially during the light phase. This increased appetite and eating schedule support the growing metabolic demands of carrying a litter. Water intake corresponds with increased feeding. Social interactions can also shift during this time, with some pregnant mice becoming more reclusive, while others might display increased tolerance depending on their established social structures.
Nesting and Pre-Parturition Preparations
As the pregnant mouse nears parturition, typically a few days before giving birth, her nesting behavior intensifies considerably. She begins to actively gather and arrange available materials, such as shredded paper, cotton, or other fibrous substances, to construct a secure and insulated nest. This instinctual behavior is a direct preparation for the arrival of her blind, deaf, and hairless pups, who will be entirely dependent on the nest for warmth and protection. The quality of this maternal nest is directly linked to pup survival, with dome-shaped nests generally correlating with higher survival rates compared to flatter structures.
The process of nest building involves several distinct actions, including carrying materials to a chosen location, fraying them into smaller, more manageable pieces by biting, and then meticulously arranging them. Mice may also engage in digging, shoveling, and push-digging to create the optimal structure and clear space around the nest. This complex construction provides a sheltered environment, minimizing the risk of pups getting scattered or lost and aiding in thermoregulation for the vulnerable newborns.
In addition to nest building, other pre-parturition behaviors emerge. The female mouse may exhibit increased self-grooming, a behavior that becomes more frequent before parturition than in the postpartum period. She might also become less active and seek isolation, creating a quiet and undisturbed space for the impending birth. These concerted efforts ensure a safe and supportive environment for the upcoming litter.
Maternal Care and Post-Parturition Behavior
Immediately following birth, which often occurs during the night, the female mouse engages in a series of critical maternal care behaviors. One of the first actions involves cleaning herself and consuming the placentas. This behavior helps to keep the nest area clean, removes potential scent cues that might attract predators, and provides the mother with valuable nutrients.
The newly born pups are entirely helpless, requiring constant care. The mother retrieves any scattered pups, gently carrying them back to the nest to ensure they remain huddled together for warmth and security. She will then position herself over the pups, providing direct warmth and allowing them to nurse, which is essential for their nutrition and development.
Nursing is a continuous process as the pups are completely dependent on her milk for the first three weeks of their lives. The mother also regularly licks and grooms her pups, a behavior that not only cleans them but also stimulates their urination and defecation and supports their overall development. Furthermore, the mother will defend her nest and pups from perceived threats, sometimes exhibiting aggression towards intruders to ensure the litter’s survival.