Reproduction and survival in the lesser spotted woodpecker. Effects of life history, mating system and age

Sammanfattning: Over 9 years, 116 breeding attempts made by individually marked lesser spotted woodpeckers (Dendrocopos minor) were followed in a study area in southern Sweden. The home-range area decreased from on average 742 ha in winter to a defended territory of 103 ha prior to breeding and 43 ha during nesting. The annual timing of the breeding varied between years but was each year synchronized with the bud burst of oaks. The mean clutch size was constant between years but showed a steep decline within the season. Early broods produced more recruited young, and the clutch size laid is suggested to be adjusted to the declining reproductive value of young, as influenced by the laying date relative to the rest of the population. Most birds died in spring and summer and the survival of both sexes was related to factors in the breeding season. Winter mortality was remarkably low, and as judged by foraging behaviour, energy was not limiting in winter. The main cause of breeding failure was the loss of the partner, whereupon the widowed bird gave up the breeding attempt. Failures occurred predominantly in pairs breeding together for the first time, leading to a considerably higher success for established pairs, who also started breeding earlier. Hence, there clearly was a high premium in retaining the mate, which may explain the strong mate and site fidelity found. An implication of this is that the fitness of either bird in the pair was influenced by the condition of the partner. This, and the overall lower survival of females compared to males, may explain the larger share in parental care assumed by the male. In situations with a skewed sex-ratio, multi-nest polygamy occurred. In 16% of the breeding attempts, males were mated to polyandrous females, and in 6% females were mated to polygynous males. Polyandrous females invested equally in all nests and polyandry was clearly succesful for the females, producing more young than monogamous females. Polygynous males appeared to invest mainly in the primary nest and were less succesful than polyandrous females.