Hibernation is a common yukkuri behavior, observed mostly in wild yukkuris, where a family or a large group of yukkuris, to preserve themselves from the cold climates of the winter and/or preserve the scarce amounts of food available during the cold months, willingly enter in a state of suspended animation, or merely limit their activities to the bare minimum, holing up in their nests (in this case the hibernation process may be called Winter Confinement). A peculiar form of Hibernation is the Rain Confinement, instead employed during the rain season in Summer.
Some weeks before winter, when the cold climate begins to sting, the parent "father" yukkuri (often a Yukkuri Marisa) begins to increase the frequency and the duration of its hunts, gathering and amassing large quantities of food and grass, while the "mother" parent takes extra care in keeping clean its offspring and use the gathered grass to make warm, softer beds for the kos. Then, according to the different stories, the yukkuri family starts its Winter Hibernation or Winter Confinement. It has to be noted that, lacking the yukkuri fandom a common canon, the choice between the Winter Hibernation and the Winter Confinement is left to the author, but it's also possible that different clans and families react to the cold in different ways.
In both cases, when the cold season starts, the "father" yukkuri seals up the entrance of their nest and the yukkuri begin their hibernation. According to some stories, the yukkuri simply begin a long, uninterrupted sleep, waking up with the first heat.
Despite taking great care to hole up in their nests, setting barriers of twigs, earth, pebbles and leaves and choosing places deep enough to ward off potential predators, hibernating yukkuris may still become easy prey for humans and large animals, able to pry the simple obstruction yukkuris places on their nest holes and consume or harm the helpless and lethargic inhabitants.
Some more organized Yukkuri Clan, instead of letting the yukkuri hibernate on their own, organize communal Yukkuri Places, large dens devoted only to sleeping hibernation where entire clans, under the direction of a Dosu (a larger leader yukkuri) and/or a Yukkuri Patchouli gather grass and cotton and ready themselves for the sleep. Being the Yukkuri Place chosen to ensure the maximum amount of safety, it's perceived as safer than a single dwelling, however Yukkuri Places have still a finite capacity, as such yukkuri are encouraged to reach them as soon as possible: late yukkuris will be expelled, left to fend for themselves in the cold climates on their own devices, more than often dying.
Large clans may have different Yukkuri Places, all placed in the clan usual territory, enabling them to avoid the search for a large cave and keep their population high in case one of the dwellings is compromised.
According to other stories, yukkuris don't get in a true lethargic status, but instead, after hoarding up as much food as they can and securing their nest, they enter in a willing state of "confinement" in which entire families, all holed up in their respective nests, do nothing but laze in their fluffy, warm bedding, rub rub together to keep themselves warmer and eat the minimum amount of food they need to stay alive, refraining from every other unneeded physical activity.
While the usually active koyukkurisare expected to suffer from this status of forced inactivity, they surprisingly react well to the forced confinement, seeing it as an opportunity to spend some quality time with their parents, endlessly rubbing without having to share their parents' attentions with necessary activities as the daily search for food and other inconveniences of the daily life, being just content of the warmth of their "Eaji place".
If the family group arranged the Winter Confinement properly, they'll all be able to survive the entire winter. However, not all families can expect to achieve such success. Most young families or yukkuri that have grown up in warmer climates may not be familiar with the proper procedures needed to survive. This includes stocking up on food, gathering bedding, etc. In such situations, survival may be dim and more unruly yukkuri may resort to cannibalism in order to survive (as seen below).
During the Winter Confinement, yukkuris are not supposed to refresh, as a pregnant yukkuri needs more food and freshly born koyukkuris need a huge amount of nutrition to grow up healthy, placing another dent in the dwindling resources of the family. However, by the rubbing employed to keep themselves warm and the miscalculation about their dwindling resources, most new Yukkuri Families end up having new koyukkuri during the hibernation and spoiling them by letting the little one have all the food they want to eat, thus dooming the entire family. It's not uncommon, in such situations, ending up with at least two generation of koyukkuris, the ones born before the Confinement and the ones freshly born, quarreling and fighting after the last scraps of food, killing each other in senseless acts of cannibalism, while the parents join the fray to "punish the uneasy little ones!" or performing Eat Up, Easy in a desperate attempt to quell their growing hunger. In most cases, if the new family survives the Winter Confinement, it's more than likely the family will consist of only the parents and possibly a lucky koyukkrui.
Rain Confinement is a peculiar form of confinement, and it differs from the winter variety because it happens in the summer season, when most climates are rainy. However, since yukkuris are especially weak to water, rain means that they can't even move in the forest, as the soaked soil would damage their feet and the rain would melt them down.
When a parent yukkuri becomes aware of an impending downpour, it begins gathering food and grass, albeit in a lesser quantity than during a Winter Confinement, while the mother yukkuri starts building new fluffy beds for the koyukkuri. When the rain starts to pour, the whole family seals off the entrance, and waits patiently for the rain to stop, rubbing and enjoying the warm of their nest and the comfort of their food.
As for Winter Hibernation, a miscalculation on part of the "father" yukkuri may be fatal to the entire family, as a shoddy or hastily made nest carries the risk of flooding, thus funneling in the nest the water the yukkuri are desperately trying to avoid.
Often felt as a joyful occasion to cuddle and play with their family, rain confinement may protract itself for days, often weeks, putting to a real test the ability of koyukkuris to survive with limited resources (despite their still lingering tendency to appreciate cuddling with their family). Though unlike Winter Confinement, koyukkuri have a much higher chance of surviving such seasons.
Pet Yukkuris and Strays
As a rule of thumb, Gutter Trash Yukkuris do not hibernate, since they've got to scavenge their meager amount of food every day or starve themselves to death. However, their lack of hibernation, coupled with the shoddy conditions of their makeshift cardboard homes or resting places expose them to the full range of symptoms Wild Yukkuri tend to avoid by hibernating or employing the "Confinements".
For example, with the extreme cold, by freezing their bottom part the yukkuri promotes constipation, especially in the premature yukkuris and the koyukkuris, forcing their parents to constantly clean them during the winter months in an attempt to keep their bodies warm and their bowel motion regular (even the paste filling near the frozen anyaru is mentioning becoming sherbet-like in its thickness), and even avoiding that, the loss of their shoddy homes end with freezing or developing dangerous molds because of the contact with damp, humid places, rainwater, and snow.
Pet Yukkuris, on the other hand and despite being aware of the possibility to hibernate, rarely if never do so. Instead they understand the concept of "Mister Heating", and keep themselves always active and thriving in the warm climate of a human housing.
However, an owner willing to witness the hibernation of a Pet Yukkuri family may still give them an elaborate Yukkurarium, conveniently placed outside the house (on a balcony or in the garden) and, when the temperature starts to drop, gradually increasing the amount of food. If the yukkuri are bright enough to survive, and if the yukkurarium is well furnished with earth and grass, the Yukkuri Family will start burrowing and preparing themselves for a Winter Hibernation or a Winter Confinement.
The Factory has since harnessed the mechanism that enable yukkuris to hibernate, thus creating the "Instant Yukkuris", a breed of Pet Yukkuris (usually bred to be docile and cheap) sold in packs of three-four individuals, able to be thawed in a simple oven or microwave and instantly able to play with their owner.
Another common use for hibernating yukkuris is selling them as food, for human or yukkuri consumption.