Oestrous and birth synchrony in Norway rats, Rattus norvegicus

I investigated oestrous and birth synchrony in 22 groups of four sibling females from puberty to the birth of their first litters. I used Monte Carlo bootstrap simulations to evaluate whether the degree of synchrony observed in these groups differed from chance. No process of synchronization was found, however. No relationship between the degree of synchrony at first oestrus (puberty) and last oestrus (prior to introducing a breeding male into each group) was found. No relationship between the degree of oestrous synchrony and birth synchrony was found. These results conflict with previous results reporting synchrony in Norway rats. I suggest that the difference between this study and the previous study may have been due to the level of analysis at which these studies were statistically analysed. In this study, I measured and analysed synchrony at the level of the group, whereas in the original study, synchrony was measured at the level of the group but analysed at the level of the individual. These results have important negative implications. First, they undermine communal care or group mating hypotheses for the evolution of ovarian synchrony. Second, they further undermine the coupled-oscillator model of synchrony in rats; and thereby its application to other species. (C) 2001 The Association for the Study of Animal Behaviour.