Prolonged Incubation and Early Clutch Reduction of White Storks (Ciconia ciconia)

Two cases of prolonged incubation by White Storks (Ciconia ciconia) were observed in the same nest in 2009 and 2010 in southwest Poland. Incubation lasted at least 59 and 65 days, respectively; i.e., 84 and 103% longer than the average incubation period. Extended incubation was accompanied by other abnormal breeding behavior. The lack of observed copulation in either breeding season, an extremely short arrival-breeding interval, and early clutch reduction suggest the eggs were infertile. This is the first record of prolonged incubation in the Ciconiidae, and probably the first record of repeated prolonged incubation by wild birds. Received 12 September 2011. Accepted 21 December 2011.