The relationship of kinship and diet selectivity to provisioning behavior in the cooperatively breeding pygmy nuthatch (Sitta pygmaea) and their influence on reproductive success

Alloparental care provided by pygmy nuthatch (Sitta pygmaea) helpers influenced the reproductive success of recipients during the breeding season in central California, 1991--1998. Reproductive success was monitored in 103 nests of pygmy nuthatches breeding in artificial nesting boxes. It was found that helpers significantly increased the number of fledglings above what was produced at nests without helpers. The timing of breeding also influenced reproductive success of pygmy nuthatches; early breeders fledged more than late breeders. Helpers increased the average hourly feeding rate to nestlings above what was achieved at nests without help. Helpers did not affect the survival rate of breeding pairs they assisted.;Pedigree analyses of individuals with known identity revealed that pygmy nuthatches most often help at nests of close relatives. Pygmy nuthatch helpers were males, and the majority were in their first adult year and assisting at the nest of one or both parents. The average level of relatedness between helpers and recipients of known identity was 0.30. It could not be determined conclusively whether or not helpers varied their level of aid with relatedness. Helpers likely gain some indirect fitness benefits via kin selection through their helping behavior.;Adult pygmy nuthatch foraging behavior was quantified over 3 years, 1995--1997, during the breeding season. Pygmy nuthatches foraged 86% of the time on one species of tree, the Jeffrey Pine (Pinus jeffreyi). They gleaned for insects in the foliage of outer branches (62% of observations) and in fairly equally in the upper, middle and lower canopy.;The diet fed to pygmy nuthatch nestlings by adults was determined via video taped recordings of prey delivery during 1995--1997. An aposematic Coccinellid beetle (Hippodamia convergens) was regularly fed to nestlings without any adverse affects to nestling growth or survival. Selectivity analyses (Manly et al. 1993) revealed that adult pygmy nuthatch do not select against H. convergens as prey items for nestlings as would be predicted if the beetles were either toxic or unpalatable. Individual adult nuthatch selectivity of H. convergens as prey items for nestlings varied widely. H. convergens may not be distasteful to birds in the wild, as has previously been reported for this family of beetles.