Decay of Apparent Individual Distinctiveness in the Begging Calls of Adult Female White-Throated Magpie-Jays

Individual recognition, the ability to correctly identify an individual, relies upon individual distinctiveness in a trait being used to determine identity. However, if such distinctiveness is not stable over time, its usefulness is limited. The purpose of this study was to assess individual distinctiveness in the begging calls of female White-throated Magpie-Jays (Calocitta formosa) recorded over different time periods. Such food solicitation calls could be selected to encode caller identity if multiple individuals within a group or neighborhood produce them. On average, a discriminant function analysis of 29 call parameters correctly assigned 51% of each female's calls to the appropriate female, suggesting that begging calls are individually distinctive. However, females that were recorded on many days were more likely to have their calls incorrectly assigned than were females recorded on one or a few days. On a short time scale, females produce calls consistently, but calls vary over longer time scales, causing a significant decrease in assignment accuracy. Such decay in accuracy raises questions about reported individual distinctiveness in other species that have not been sampled over longer time periods or on multiple occasions. In White-throated Magpie-Jays, floater males looking for fertile females, or group members determining whom to feed could benefit from individuality in begging, but they may need to integrate identity information over multiple calls in order to correctly determine sender identity.