Parental care and social mating system in the Lesser Spotted Woodpecker Dendrocopos minor

The sexes' share in parental care and the social mating system in a marked population of the single-brooded Lesser Spotted Woodpecker Dendrocopos minor were studied in 17 woodpecker territories in southern Sweden during 10 years. The birds showed a very strong mate fidelity between years; the divorce rate was 3.4%. In monogamous pairs, the male provided more parental care than the female. The male did most of the nest building and all incubation and brooding at night. Daytime incubation and brooding were shared equally by the sexes, and biparental care at these early breeding stages is probably necessary for successful breeding. In 42% of the nests, however, though still alive the female deserted the brood the last week of the nestling period, whereas the male invariably fed until fledging and fully compensated for the absent female. Post-fledging care could not be quantified, but was likely shared by both parents. Females who ceased feeding at the late nestling stage resumed care after fledging. We argue that the high premium on breeding with the same mate for consecutive years and the overall lower survival of females have shaped this male-biased organisation of parental cart. In the six years with best data, most social matings were monogamous, but 8.5% of the females (N = 59) exhibited simultaneous multi-nest (classical) polyandry and 2.9% of the males (N = 68) exhibited multi-nest polygyny. Polyandrous Females raised 39% more young than monogamous pairs. These females invested equal amounts of pal-ental care at all their nests, but their investment at each nest was lower than that of monogamous females. The polyandrously mated males fully compensated for this lower female investment. Polygynous males invested mainly in their primary nest and appealed to be less successful than polyandrous females. Polyandry and polygyny occurred only when the population sex ratio was biased, and due to strong intra-sexual competition this is likely a prerequisite for polygamous mating in Lesser Spotted Woodpeckers