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Ancestor: South-West Catland River Mice 

Size: 20-25 centimetres excluding the tail, 30-35 with the tail.

Dietary Needs: It's most prized prey is the river snails, which they will hold in their paws and "punch" through the shell with it's incisors. It will then work on expanding the damage to the shell from that starting point, to make it easier to extract the living snail. However, some snails present great difficulty by being covered in very slippery slime, shell included. Having webbed, basket-like paws helps somewhat.

Being more carnivorous than the ancestral mice, snail-punching mice also eat small (usually juvenile) crustaceans, small fish and fish spawn. But they will also eat grains and fruit to assist with fattening up for winter.

Life Cycle: Very similar to it's ancestor, with short oestrus cycles in the female over spring and early summer until impregnated. Females also locate males the same way as before, following urine trails and ultrasonic chirps. Multiple males may fight over a female, and such fights can get bloody very quickly, more so if the competition is intense from many males. Their range is more confined to freshwater sources, and as such there is heightened competition for nesting. Females compete hard for space. They do this by standing tall and sizing up and bearing teeth. They have to stay healthy and strong for much longer than the males if they want to pass on their genetic information because they must raise the pups to adulthood, and with pups can't afford to be nursing wounds, so are more risk averse and less inclined to violence. But if no one female backs down, conflicts can move on to shoving and if that doesn't settle it, full-blown fights can occur between females.

Their instinct is to give birth in a deep, cosy, moss-and-fur-lined burrow on a good riverbank and this drive can become desperate if prime burrowing spots become full. If a female ends up giving birth in the open, she will likely be too stressed to raise the pups, will eat them to salvage some spent nutrients and energy, then will move out of the area to try to find less crowded habitats with recent male scent trails and try again there. Very successful "winner" females may keep the same burrow year-after-year.

Successfully raised pups take about a month to wean, and about 2 and a half months to become independent, but their sexual maturity will be delayed until the following year, except in the case of very early starters (raised in a warm early spring), who may sexually mature in the early summer and produce their first litter that very same year.

Other: These mice are much more winter-adapted than their ancestors. They go through a fattening period on the autumn, and in winter will spend a lot of time sleeping and minimizing calorie usage. A lot more males die in the winter than females, because females usually have a burrow all ready to go for the winter. But males and unsuccessful females are forced to scramble for somewhere to keep safe and save calories. They go into bursts of hibernation, where their body temperature drops (again, to minimize calories burned) and they seem almost dead. But they will wake and emerge every few days, or up to a week between. This is to try to find calorie top-ups or pass waste.

Individuals living at the North of their range can make it through the winter without a burrow, but where rivers freeze there isn't enough food for them, so they must keep inactive if they are to survive.