Nelson D.A. & Poesel A. (2007). “Segregation of information in a complex acoustic

signal: individual and dialect identity in white-crowned sparrow song.” Animal

Behaviour (74): 1073-1084.

The authors test whether the two components present in white-crowned sparrow song act as redundant signals of male dialect or whether they are multiple signals that have different functions. White-crowned sparrow song includes both an introductory phase or ‘note complex’ and a subsequent ‘trill’. In order to elucidate the functions of these two phrases, the authors first assessed the variability of each phrase within a population of males with the same dialect and among a subset of these males in Puget Sound over two years. Recordings of these males’ calls were made and 13 variables were measured on the first three notes in each call. These measurements included the frequency at the beginning and end of each note, note length, length of silence between notes and mean number of notes.

The authors assessed variability within the group of 85 males and among a subset of six males in the aforementioned aspects of note complex and trill elements. In addition, the authors performed a playback experiment on breeding territories where fifteen males were randomly presented 3 different stimuli: i) a neighbor’s song ii) a neighbor’s song with a substituted stranger’s trill and iii) a neighbor’s song with a substituted stranger’s note complex. Male response to playbacks was measured by the change in his song rate and the change in his distance from playback source.

The resulting analysis demonstrated considerably more variation in note complexes than trills in both years. Also, although both trills and note complexes differed among individuals, note complexes served as a more reliable predictor of individual identity. Furthermore, the authors found that males moved closer to the speaker and sang more when presented with a neighbor’s song with a substituted note complex than when presented with either of the other two stimuli suggesting males respond more to the information coded in the note complexes when determining male identity. These combined results are consistent with a ‘multiple messages’ hypothesis where each phrase encodes for different information; trill most likely establishes dialect while note complex determines individual identity.

As we discussed in class the stereotypy of a signal that codes for inclusion in a specific group is excepted among group members thus it is not surprising that the trill which shows very little variation among dialect members may encode for group identity. Also, we discussed that the simultaneous need for individual recognition and for group recognition may cause variation among group members in a specific element of the signal; in this case, males’ trill calls conform while the note complexes allow enough variation for individual recognition. Finally, as concluded in this study, we learned that the existence of multiple signals (e.g. a trill and a note complex) would arise even though costly if each signal has a different function or if each signal carries different information about the some characteristic.