Figure 1 - Mean (± SEM) frequency of sniffing, lateral attack, frontal attack and biting the intruder male by the lactating female with cross-fostered pups during 10-min recording sessions. F8+P8 (female on the 8th postpartum day raising 8-day-old pups); F8+P18 (female on the 8th postpartum day raising 18-day-old pups); F18+P18 (female on the 18th postpartum day raising 18-day-old pups); F18+P8 (female on the 18th postpartum day raising 8-day-old pups). N = Number of animals in each group. *P<0.05, F8+P18 compared to group F8+P8; +P<0.05, F18+P8 compared to group F18+P18 (Student t-test).