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 mino r were studied in 17 woodpecker territories in southern Sweden during 10 ye ars. The birds showed a very strong mate fidelity between years; the divorc e 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 probabl y necessary for successful breeding. In 42% of the nests, however, though s till alive the female deserted the brood the last week of the nestling peri od, whereas the male invariably fed until fledging and fully compensated fo r the absent female. Post-fledging care could not be quantified, but was li kely shared by both parents. Females who ceased feeding at the late nestlin g stage resumed care after fledging. We argue that the high premium on bree ding with the same mate for consecutive years and the overall lower surviva l 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) pol yandry and 2.9% of the males (N = 68) exhibited multi-nest polygyny. Polyan drous Females raised 39% more young than monogamous pairs. These females in vested equal amounts of pal-ental care at all their nests, but their invest ment at each nest was lower than that of monogamous females. The polyandrou sly mated males fully compensated for this lower female investment. Polygyn ous males invested mainly in their primary nest and appealed to be less suc cessful than polyandrous females. Polyandry and polygyny occurred only when the population sex ratio was biased, and due to strong intra-sexual compet ition this is likely a prerequisite for polygamous mating in Lesser Spotted Woodpeckers.