ON THE QUANTIFICATION OF SUCKLING INTENSITY IN PRIMATES

The inhibitory effect that suckling has on the reproductive function o f primate mothers varies as a function of the intensity with which the y are suckled. Here we present an easily computed index of one paramet er of suckling intensity, namely the temporal patterning of suckling b outs. High intensity suckling is characterized by frequent nursing bou ts demarcated by short interbout intervals. Therefore, our suckling in dex is based on the brevity of observed interbout intervals, more spec ifically the proportion of such intervals that fail to exceed a criter ion length. The index is an appropriate means of making interspecific comparisons of the development of infant suckling and is well suited f or application to field data that include interbout intervals that wer e not observed in their entirety. To demonstrate its utility, we apply the index to field data collected on the suckling behavior of free-ra nging rhesus monkey (Macaca mulatta) infants in India. In this context , we demonstrate that, in rhesus, between-infant differences in suckli ng intensity manifest themselves early in the postpartum period and co ntribute to between-female differences in the timing of first mating p ostpartum. (C) 1998 Wiley-Liss, Inc.