Cooperative and Solitary Mobbing to Defend Offspring in Wild Gray Mouse Lemurs, Microcebus murinus

Gray mouse lemur, Microcebus murinus, mothers either cooperatively breed plurally with kin or breed solitarily. We describe the first observations of cooperative and solitary mobbing to defend offspring by wild cooperative breeding gray mouse lemur mothers in Kirindy Forest, Western Madagascar. We observed four groups of cooperatively breeding mothers and their offspring daily between 18:00 and 04:00 from January 1 to 15, 2023. Cooperative mobbing was observed twice, and solitary mobbing by a single cooperative breeding mother was observed once. There was one Malagasy tree boa, Sanzinia madagascariensis, per mobbing event. Mothers solitarily mobbed by directly approaching within 1 m of the boa, walking and changing distance while within 1 m of the boa. In addition to the solitary mobbing behaviors, cooperatively mobbing mothers approached the boa together from the same or different directions or alternated, and they gathered around the boa. Mothers collaborated in the context of offspring defense from predators and performed different complementary tasks: mobbing while another provided alloparental care by guarding the offspring of the association, that is, babysitting. Mothers performed similar mobbing behaviors and occasionally synchronized in time or coordinate in time and in space to approach from different directions and gather around the boa. Mothers did not come in contact with the boas during mobbing but kept a distance of at least 20 cm. On two mobbing events, the boa rose up with its head facing the mobbing mothers and climbed down the tree after the mobbing. Cooperative mobbing to defend offspring likely evolved by kin selection but reciprocity and an interaction between kin selection and reciprocity cannot be ruled out, since gray mouse lemur mothers cooperatively breed with kin and basically allonurse reciprocally.