Inclusive fitness theory is an important theoretical framework in demonstrating the evolution of social behaviors. However, in the scenario of caring for offspring, it is difficult for the inclusive fitness theory to demonstrate the errors parents made in offspring selection, either rejecting their own offspring (type I error) or accepting the offspring of others (type II error). To address why parents make errors in caring for offspring and the relationship between making errors and parental ability of offspring recognition, we designed a series of experiments in the azure-winged magpie (Cyanopica cyanus). By manipulating the nest spatial position or cross-fostering chicks, we examined parental care strategies for the manipulated offspring and tested whether offspring age and parent-offspring familiarity affected the occurrence of both errors. In the nest resettlement experiment, the probability of type I error significantly increased with nest-moving distances while decreased with offspring ages. In the cross-fostering experiments, the probability of type II error significantly decreased with the age difference between cross-fostered chicks. In the experiments of reselection between familiar offspring and unfamiliar unrelated chicks or between unfamiliar offspring and familiar cross-fostered chicks, the probability of both errors was closely related to the time when parents were deprived the association with their offspring. Given offspring phenotypic traits become individualized and fixed with their growth, it imposes an aging effect on parental ability of offspring recognition. Parental errors in offspring selection depend largely on the age of offspring when the environmental or offspring signals are manipulated.

Data used in the experiment were collected in the field.