Helper systems where non-breeding group members assist with the territorial defense and care of the young are widespread throughout the animal kingdom. In this study, we examined the role of subordinate Eurasian beavers (Castor fiber) as helpers in a population in southeast Norway. We conducted playback scent experiments, simulating a territory intruder. In total, we recorded 349 territorial reactions, and found that subordinates reacted towards simulated intruders according to their proportion in the family group, i.e. they helped with territorial defense. Subordinates reacted more with increasing age of their parents suggesting that they might take over territorial duties with increasing age of their senescing parents. However, the number of subordinates in a family group did not increase the total number of responses. Further, we examined whether the number of subordinate beavers within the family group affected the body weight of kits (n = 120) while controlling for other factors, hypothesizing that subordinates would aid with food provisioning. The body weight of kits was not related to the number of subordinates in the family group, but decreased with increasing precipitation. In conclusion, subordinate beavers might play a role in territorial defense, but did not affect offspring weight. By remaining in the natal family group, subordinates likely learn important behaviours, e.g. territorial defense, that will increase their chances to successfully gain and defend a territory of their own.