Norway rats recruit cooperation partners based on previous receipt of help while disregarding kinship.

Norway rats are known to liberate trapped conspecifics, which implies an empathic response to the deplorable situation of the captive. If this is an altruistic behavior reflecting an evolved decision rule, the requisite fitness enhancement to the actor may result either from close relatedness or the expectation of future returns. Neither potential effects of relatedness nor of reciprocal returns have yet been examined.

Assessment of help value affects reciprocation in Norway rats.

Wild-type Norway rats reciprocate help received in a well-replicated experimental food-giving task, but the criteria to appraise the received help's value are unclear. We tested whether quality or quantity of received help is more important when deciding to return help, and whether partner familiarity and own current need affect this evaluation. We experimentally varied recipients of help's hunger state, and familiar or unfamiliar partners provided either higher caloric food (enhanced quantity; carrots) or food higher in protein and fat (enhanced quality; cheese).

Reaching Out for Inaccessible Food Is a Potential Begging Signal in Cooperating Wild-Type Norway Rats, .

Begging is widespread in juvenile animals. It typically induces helpful behaviours in parents and brood care helpers. However, begging is sometimes also shown by adults towards unrelated social partners.