Peregrine Falcons near Canberra bred slightly earlier following a dry winter. The laying season was shorter and ended earlier when there were many raindays between June and September. The number of raindays in July and August accounted for 77% of the variation in the length of the laying period. A warm, dry winter was associated with a lengthened laying season. A longer, slightly earlier, laying season resulted in more pairs laying and therefore more young raised by the population. Late-laying pairs were only slightly less successful than early-laying pairs. Pairs with alternative nest(s), or with a well-drained nest, had a longer egg laying season, and more of them laid, than other pairs. Thus, pairs holding a territory with a high quality nest were advantaged over those that were not, because of the direct effect of rain.