Local Song Traditions in Indigo Buntings: Cultural Transmission of Behavior Patterns Across Generations

Abstract

Songs of indigo buntings were recorded at the E. S. George Reserve in southeastern Michigan from 1963 to 1980. A computer program was developed for the recognition of similar song patterns, using a catalog of audiospectrogram song figures and the sequence of the song figures. Neighboring buntings often matched their songs, usually with no more than five birds having the same song. Buntings from remote populations rarely matched the song of the George Reserve buntings. The probability of survival of song traditions was estimated from the historical data on the local songs. Most bunting songs of the 1960's no longer occur locally and either have disappeared or have altered beyond recognition by cultural drift. A few song types nevertheless have persisted in the local population for 15 years. Song types of adult buntings had an estimated annual exponential decay rate of 0.18 and an exponential half-life of 3.8 years. Estimated survival rates of songs were higher when more liberal criteria were used to recognize cases of matching songs, indicating that certain song traditions have changed through the accumulation of learning errors in cultural evolution. Survival of marked individual adult buntings was only a third of the survival of their song types. Survival of songs was similar whether estimated forward in time from the early samples or backward from the last samples. The equivalence is consistent with a random neutral substitution model of cultural evolution rather than with a competitive model that resembles an intense natural selection leading to many descendants being derived from a few founders. The local songs of adult indigo buntings are relatively long-lived behavior traditions that persist by social song learning outside of any family kinship line across several generations.