Yellow-necked mice are nocturnal, being active for a single period each night (4). They feed on fruit, seedlings, buds and the odd invertebrate (4), often storing food within tunnel systems (3). All mice engage in 'refection' in order to fully digest food; they eat soft faeces that have passed through their digestive system once, allowing carbohydrates to be fully digested (3).
Breeding occurs from March or April until October, although under some circumstances breeding may occur throughout the year (4). Before mating, males are known to produce a string of ultrasounds, which may serve to pacify the female (3). Gestation takes 25 or 26 days (3), and the litter, which consists of 2 to 11, but usually five young (4) is born at night in a nest (3). Nests may be made in underground tunnels, inside hollow logs, bird or dormice nesting boxes or in dense vegetation (3). Around three litters are produced each year (4), and females are able to conceive whilst still suckling the previous litter (3). The young are fully weaned after about 18 days, and usually start to breed the year following their birth, but if they were born early in the year they may breed during the year of birth (4). Dominant males may be aggressive, and have been reported to chase and even kill juveniles (3). This species does not hibernate; during winter a number of these mice may group together when sleeping for extra warmth (3).
Yellow-necked mice are adept climbers, and as a result they feed in trees and bushes and enter houses more often than wood mice (3). Predators such as weasels and owls are often avoided by means of impressive leaps to safety, or by shedding the skin of the tail if it is gripped anywhere other than its base, allowing the mouse to escape. The skin does not grow back; instead that area of the tail dies and falls off (3).