Signature Systems and Kin Recognition

SYNOPSIS. This paper examines mechanisms of individual identificationin the kin recognition process. In type 1 kin recognition, theindividual (e.g., a parent) learns the identifying cues (the"signature") of particular kin (e.g., offspring) at some stagewhen there are reliable contextual cues as to kinship (e.g.,the parent finds the young in its nest). These kin are subsequentlyrecognized via their signatures in situations in which contextualevidence of kinship is lacking. The primary selection pressurein this case is for a mechanism that can generate a large numberof distinctive signatures, and thus permit recognition in largegroups. I develop a model that predicts the necessary informationcapacity of a signature system, and I test this prediction forthe signature call of the bank swallow (Riparia riparia). Themeasured information capacity of 17 bits corresponds well tothe prediction and, moreover, is substantially greater thanthat of the homologous call of the similar but non-colonialrough-winged swallow (Stelgidopteryx ruficollis). In type 2kin recognition, reliable contextual evidence as to kinshipis absent at all times, and kin must be recognized via a signature-matchingprocess. For example, the individual might compare its own signatureto that of the unknown individual, inferring kinship if theirsignatures are sufficiently similar. I describe a multi-locusgenetic signature mechanism that would permit discriminationof kin from non-kin, and suggest how this model might be tested