When do field mice breed? - briefly
Field mice reproduce from early spring through late autumn, with the majority of litters born between April and May and a secondary peak in September.
When do field mice breed? - in detail
Field mice begin reproducing in the spring, when daylight lengthens and temperatures rise. The first estrus cycles appear after the winter dormancy, typically in March in temperate zones. Breeding continues through the summer and may extend into early autumn, with a decline as night lengthens and food supplies diminish.
Key points of the reproductive cycle:
- Sexual maturity is reached at 6‑8 weeks of age; juveniles can join the breeding population within a month of weaning.
- Gestation lasts 19‑23 days, depending on species and ambient temperature.
- Litters contain 4‑8 offspring on average; larger litters are common in years with abundant resources.
- Females are capable of producing 3‑5 litters per season if conditions remain favorable.
- Peak conception periods occur in late April–early May and again in July, aligning with maximal vegetation growth and insect activity.
Geographic variation influences timing. In northern latitudes, the breeding window narrows to May‑July, while in southern regions it may start as early as February and persist until October. Mild winters can trigger early estrus, whereas harsh winters delay the onset by several weeks.
Environmental cues that regulate reproduction include:
- Photoperiod: increasing day length stimulates hypothalamic release of gonadotropin‑releasing hormone.
- Temperature: optimal breeding temperatures range from 15 °C to 22 °C; extreme heat suppresses fertility.
- Food availability: abundant seed and plant matter accelerate ovarian development and increase litter size.
- Population density: high density can suppress breeding through pheromonal signals.
During the breeding season, males establish territories and display increased aggression, while females construct nests in concealed locations such as under dense vegetation or within burrows. Nesting materials consist of shredded plant stems, grasses, and soft debris, providing insulation for the altricial young.
Reproductive activity ceases as days shorten in late summer. Hormonal changes lead to estrus suppression, and females enter a period of reproductive quiescence that can last until the next spring. This annual cycle ensures that offspring are born during periods of maximal resource availability, enhancing survival rates.