In the wintertime, there are "living crystals" that grow and expand in the Cave. A strange, unidentified spore appears to be able to implant itself into the crystals, which spawns the egg. The eggs grow in the darkest and coldest crevices where these crystals are found. The Science and Research Center in Ark City believes that these Cave crystals are powered by an inexhaustible life form but they have not formally experimented on the crystals in lab environments to verify the hypothesis.
Who knows what beast these crystals may bring into the world...
Pipitallo creatures are bats that are fully powered by ice. It is their blood and their energy. They don't eat anything except the Cave crystals from which they came. They can only survive in cold environments and melt above freezing temperatures (both eggs and their any of their hatched forms). As a result, their summer home is the Cave itself and they venture outside of it only in the wintertime.
Thankfully, Pipitallos are pretty good at understanding the weather and predicting it, so they are rarely caught in a bad situation (i.e. too far from the coldness of the Cave) when things thaw in the transition to spring.
Pipitallos are a reserved creature that don't interact with much outside of their own kind. They keep to themselves. They like their Cave. They do not like intruders. If you threaten their home, they will swarm and attack viciously with their razor-sharp ice wings. They protect Cave crystals at all cost and are willing to sacrifice their life, if it means other Pipitallos survive.