Annual and seasonal reproductive trends in the Lesser Spotted Woodpecker Dendrocopos minor

Annual and seasonal variation in reproductive timing and performance were s tudied in a population of the Lesser Spotted Woodpecker Dendrocopos minor o ver 10 years in southern Sweden. The median laying; date of the first egg v aried by up to 17 days between years, being generally larger than the varia tion of laying dates within years. Neither clutch size, brood size in succe ssful nests, fledging success in successful nests nor mean nestling weight differed significantly between years. There was no trend for mean clutch si ze to vary between early and late years. In spite of a more than threefold variation in population size, no reproductive variable demonstrated an appa rent density-dependence. Within the season, clutch size declined steeply wi th increasing clutch initiation date, whereas fledging success and nesting success did not, leading to a trend in brood size almost identical to the t rend in clutch size. The survival prospects of fledged young declined with increasing clutch initiation date, and it is argued that the clutch size la id is a strategic adjustment to laying date. Out of 124 breeding attempts, 34% did not produce fledged young. In 9% of the breeding attempts, pairs la id no eggs. At least 20% of the breeding attempts failed after egg-laying. The most common cause of breeding failure was loss of the breeding partner followed by nest abandonment (greater than or equal to 40% of the failures) . Only 16-28% of the failures were due to predation on the nest. Most compl ete failures, and also partial losses from nests, occurred at the early bre eding stages. It is argued that the early nestling phase may be a critical stage, which the woodpeckers adjust to coincide with the seasonal food peak , explaining the strikingly late breeding season compared with other non-mi grant species.