The influence of familiarity and temperature on the huddling behavior of two mouse species with contrasting social systems

•Huddling is an effective way to reduce heat loss and increase survival.•Mound-building mouse and house mouse differ in their social systems.•Familiarity and temperature had different effect on their huddling behavior.•Huddling is a good indicator of tolerance between individuals. Huddling with other individuals is an effective way to reduce heat loss. This cooperative behavior requires that the individuals tolerate each other’s presence at least for a certain time or under certain circumstances. In our study, we investigated the effects of ambient temperature and familiarity on the huddling behavior of two closely related mouse species, the mound-building mouse (Mus spicilegus) and the house mouse (Mus musculus musculus). While their geographic distribution overlaps, their social systems differ in many aspects. Whereas house mice are territorial, mound-building mice tolerate each other and live in groups during winter. In laboratory experiments we found that familiarity and ambient temperature influenced the huddling behavior of both species. Familiar individuals were more likely to huddle, but while mound-building mice did so at all temperatures, huddling in house mice increased with lower temperatures. Our results are consistent with the previous knowledge about these species’ social systems and might provide us with more details about their sociality. Investigating huddling behavior might be a good way to measure social tolerance between individuals within a species and compare social systems of different species.