On a yearly timescale, colonial birds breed approximately synchronously in an annual pulse within a time window set by photoperiod. If a nesting colony is sufficiently dense, higher frequency reproductive oscillations on a daily timescale can form within the annual pulse due to synchronized ovulation cycles. Tight annual pulses do not afford sufficient time for ovulation cycles to synchronize. Data from a colony of Glaucous-winged Gulls support the hypothesis that the degree of yearly synchrony is inversely related to the degree of ovulation synchrony. Yearly synchrony may be advantageous due to predator satiation (Fraser Darling effect); similarly, ovulation synchrony may be advantageous due to cannibal satiation during El Nino years with high cannibalism rates. This suggests a tradeoff between strategies of synchronous reproduction on two timescales.