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The ontogenetic development of vocal communication was studied in 23 young red squirrels (Tamiasciurus hudsonicus) from four litters born in captivity. The age of appearance and sonogram analysis of the young's vocalizations are presented. In the newborn, discomfort and distress calls are the first vocalizations to appear. With the development of hearing, differentiation of distress and threat calls is noted and a contact call commences. Various alarm and threat calls occur when the young make their first appearance outside the nest. Territorial calls are heard for the first time around weaning.