Social stimulation in concert with environmental factors may influence the degree of reproductive synchrony among colonial breeders. Synchronous breeding has been shown to enhance reproductive success by decreasing predation. Although Common Murres (Uria aalge) typically have a cyclic pre-lay attendance pattern, during one of four consecutive breeding seasons we observed one acyclic pre-lay period (1999). The present study investigated how differences in pre-lay attendance patterns may influence breeding synchrony and reproductive success in a Common Murre sub-colony on Great Island, Newfoundland. Compared to the cyclic pre-lay period (2000), the acyclic pre-lay period showed: i) less synchronous egg-laying, ii) pairs spent less time together at their site due to the overall lower attendance by both sexes, but particularly by females, and iii) higher predation during early and first half of peak egg-laying, although overall reproductive success did not differ between years due to high re-laying rates. These results suggest that cyclic attendance during the pre-lay period of Common Murres may influence breeding synchrony within a sub-colony, which may reduce predation during early incubation and late chick rearing.