Mouse pup urine as an infant signal

Drops of urine from donors of different ages and sexes were applied to the anogenital regions of 19-day fetuses, killed by freezing, that ordinarily are weak in stimulating parental care. These fetuses were then presented to virgin, naive albino mice (Mus musculus). In Experiment 1, fetuses treated with urine of 6-day-old pups were more stimulating than fetuses treated with water. Differences in contact, picking-up, retrieval, licking and self grooming were significant. The sex of the donor revealed no effect. In Experiment 2, urine from 10-day-old pups was found to be more effective than urine from 4-day-old pups, with different effects on contact and retrieval. Urine from pups was also more effective than urine from adults, because of different effects on contact, picking-up, retrieval, licking and nest building. The effects of urine from adult virgin females differed less from those of pup urine than did the effects of urine from adult males. Compared with the latter the adult female urine had different effects on picking-up, licking and cannibalism. Speculations are made about an infant factor that might be still active in the urine of adult females.