The Primate Isolation Call: A Comparison with Precocial Birds and Non-primate Mammals

Abstract

Evolution took a major turn when mammals first walked the Earth. Reptilian infants typically develop within the egg to be self-sufficient at hatching. Most mammalian infants, however, require their mother for warmth and sustenance during their earliest developmental period, and will die if they fail to receive these life-sustaining gifts. Infant birds, like reptiles, hatch from eggs, but for most species, they are fed and cared for by one or both parents until they can fend for themselves. As with mammals, infant birds depend on a caregiver to survive during their earliest developmental period. It should not be surprising, then, that infant birds and mammals have evolved vocal signals to alert their caregiver should the infant become separated from its nest or caregiver. With birds, the best developed of these so-called “separation calls” or “isolation calls” appear to be in precocial species, where the chicks can locomote soon after birth and get their food by foraging with the mother. This sometimes results in occasions when the chicks become separated from the mother, hence the adaptive value for auditory signals to efficiently bring about reunion. In some species, these separation calls continue into adulthood. For example, in the Bobwhite Quail (Colinus virginianus), adults use the separation call in the same way as chicks do, namely when a covey becomes separated (Baker and Bailey, 1987a). As is the case for a number ofmammalian species (discussed below), Bobwhite Quail can recognize their covey mates based on the auditory information in their separation calls (Baker and Bailey, 1987b). In other species (e.g., the Japanese quail, Coturnix), the neonatal isolation call of chicks matures into “crowing,” a call associated with reproduction (Takeuchi et al., 1996).