The crèche (from French) in zoology refers to care of offspring in a group or colony. Many species such as common eider, lions, and penguins form crèches and exhibit group behaviours. Crèches can serve different functions and purposes depending on the species and the environment. For example, some crèches may aid in defence while other crèches may aid in feeding and protection from harsh weather conditions. This form of group living has evolved over time to become advantageous to the species. Studies have shown that by participating in group living, species will increase their inclusive fitness since their young will be in a better condition to reproduce and carry on the line of descendants in the species. Crèche behaviour in eiders, Somateria mollissima In the Common eider population, after giving birth to their eggs, the mother will incubate them until they hatch. The mothers will hear a signal from the juvenile's which will cause her to move away and open the nest for the eggs to hatch safely. Once the eggs have hatched, the mother will either abandon her young, care for her young alone or join a multi-female crèche. In the common eider species, if the crèche group behaviour is followed, the formation of the crèche will occur as soon as the juveniles leave the nest, and the group behaviour will last for a long period as the mother provides parental care to her young as they develop. Studies have shown that while the parental care mode can change over the years, 46% of female eiders will care for their young through a multi-crèched environment. Female eiders can care for their young through a true crèche or a transient crèche. In a true crèche, the mother will choose a select group of females to live and care for her young with for a long period of time. Contrastingly, in a transient crèche, the female and her young will not stay with the same group for a long duration and they will move through different crèches rather than stay with one permanent group. These transient crèches will normally form about two weeks after the juveniles hatch so they have time to experience social interaction with their mother and siblings first. The females and young in the true crèches showed a higher level of overall condition compared to the transient crèches. Another study provided evidence that common eiders who do not