Fig. 1. Dams shepherd virgins to nest.

a, System for continuous monitoring of behaviour and neural activity. b, Ethogram showing activities of co-housed dam and virgin mice over a period of four days. c, Co-housing with dam and pups led to earlier retrieval by virgins. Left, individual retrieval rates. Right, mean retrieval probability. d, Day of retrieval onset was earlier in D+ virgins. e, Time in nest for dams and co-housed virgin mice. f, Correlation between virgin nest entry during day 1 and virgin retrieval at the end of day 1. g, Illustration of shepherding behaviour; arrows, movement direction; dashed circle, nest area. h, Probabilities of dam starting (yellow) and ending (orange) chasing of a co-housed virgin, relative to nest position (circle indicates the nest, radius approximately 10 cm). i, Distances from nest of dam→virgin chases. j, Frequency of shepherding events (grey, individual dyads; red, daily averages across cages) was more frequent than dam→virgin chases in the absence of pups (0.2, indicated by dashed line). k, Correlation between shepherding during day 1 and virgin retrieval at day 1 end. Data are mean ± s.e.m.; *P < 0.05, **P < 0.01.