Avian parental infanticide is apparently a rare phenomenon judging from the scant reports in the literature. However, unexplained cases of single nestling disappearance or of apparent fall from the nest are rather common and are routinely attributed to parental eviction of dead nestlings, single chick predation or dislodging of nestlings through errors by nestlings or parents. During long-term studies of pied flycatchers Ficedula hypoleuca in central Spain 29 cases of eviction from the nest cup of mostly hatchlings or small, heterothermic nestlings were recorded, leading invariably and quickly to death. Parental errors and failed attempts to predate single chicks are unlikely in these cases. Although the incidence of recorded evictions was mostly below 5% of nests, it reached higher levels in years and populations where reproductive success was low. Some cases were preceded by prior egg eviction. In these studies, there were unexplained disappearances affecting 3.7% of eggs laid which amounted to 20% of all losses. During studies of three other passerine cavity nesting species, similar cases were observed. The rarity of reports of parentally evicted nestlings is apparently based on the difficulty of directly observing parents evicting live nestlings but may also be due to observer bias as ejections of dead nestlings, erroneous dislodgings or single-chick predation events are also rarely observed but are normally given as reasons for single-chick losses. Field researchers should attempt to determine the real causes of partial brood loss before assuming that parsimony excludes parental infanticide through eviction.
Article first published online: 29 DEC 2011
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