It is widely accepted that the first White Storks to arrive at a nest remain there to breed. In contrast to this belief, the paper describes the replacement of at least three males and at least one female at one nest in SW Poland during the spring of 1994. The first pair occupied the nest for 5-8 days, the second pair for one day, and probably only the third pair remained at the nest to actually breed. Additional data on arrival patterns show that such replacements of non-breeding storks may occur much more frequently than was previously thought, especially in areas of intense migration. Consequently, the most common phenological observations (e.g. the arrival dates of the first and second White Storks) are not really useful for defining the timing of breeding. It is suggested that the beginning of nest occupancy should be defined by the beginning of the permanent stay of the second partner, and not just by the date of the birds' first appearance.
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