Social inhibition of song imitation among sibling male zebra finches

1. Social inhibition of song imitation among sibling male zebra finches Results Ofer Tchernichovski and Fernando Nottebohm Proc. Natl. Acad. Sci. USA Vol. 95, pp. 8951-8956, July 1998 Methods Thirty-four clutches of one to five male siblings from 32 pairs of zebra finches that had bred before were used in the work reported here. New hatchlings were identified and tagged on a day-to-day basis. There were 4 experimental groups: Group 1: One early-hatched male from each of 10 clutches of variable size was kept in a soundproof cage with its father after day 30 and until day 90. Group 2: Another five clutches of two to five male siblings and their sisters kept with their parents for the same duration. Group 3: This group consisted of 16 clutches. The siblings from each clutch were housed with their parents in the same cage. These cages were kept in a room with many other clearly visible zebra finches until day 90. Group 4: Three clutches of three male siblings were kept in three separate rooms. Between day 30 and day 90 the siblings were housed in separate cages around their parents’ cage so that each sibling could approach its father and other siblings and interact with them across the wire wall. Judging Similarity At least 10 renditions of a song by each bird was recorded. Each note of each song was compared to a similar, if present, note of the father. Similarity was then judged and given a value of 1 to 5 based on fundamental frequency, frequency modulation, duration, and position of the note in each motif. Whole song comparisons were then completed, based on “relative duration” and the number of similar notes in a son and father’s song (Fig 2). Abstract A male zebra finch, Taeniopygia guttata, kept with its father until adulthood develops an imitation of its father’s song motif. It is reported here that the completeness of this imitation was sensitive to the social or auditory context in which the bird grew up: the greater the number of male siblings in a clutch, the shorter the mean duration of their song, termed fraternal inhibition. This fraternal inhibition was avoided by members of a clutch that developed the song first. Fig. 3: Differences in mean relative song duration and mean similarity between group 1 and group 2. In 10 cases of male zebra finches kept singly in isolation with their father between days 30 and 90, the mean relative duration of their song motif was 101 +/-3 %, and the mean similarity was 91+/-3%(fig 3). In contrast, the song motifs of 18 male zebra finches raised in five clutches of two to five male siblings until the age of 90 days (group 2) had lower mean relative durations (84 +/- 6%) and lower mean similarity (73 +/- 5%) than those of the single male siblings (fig. 3). Results similar to those found in group two were found for group 3 and group 4, when clutches were kept in rooms that housed many other birds. As the number of male siblings in a clutch increased, the mean relative duration of the siblings’ song motifs decreased, as did the mean similarity. The study speculated that siblings hatched earlier would tend to acquire their song motif earlier and produce better imitations of the father’s song. Surprisingly, imitation was incomplete in the early hatched siblings of each clutch (relative duration = 65+/- 6%; similarity = 67+/- 7%) but not in late-hatched birds (relative duration = 88 +/- 6%, similarity =81 +/- 7%). To answer how this comes about in ontogeny, the study made recordings of song in five clutches of two to five male siblings raised by their parents in soundproof rooms (group 2). The results show that the first siblings to produce recognizable versions of their adult motif (example of adult motif in Fig. 4) also produced the most accurate imitation of their father’s motif. Introduction Song development in the zebra finch occurs within the first 90 days after hatching, which is known as the so called “sensitive period” of song growth in birds. Songs of father and son zebra finches are remarkably similar when the son grows up in the company of the father, which has been determined to be a non-genetically influenced phenomena. This study investigates song imitation in clutches with different numbers of male offspring. Discussion Bohner (1983) suggested that inaccuracies in song imitation might serve a purpose in zebra finches e.g. by promoting the uniqueness of each juvenile’s own song when several siblings imitated the same model. This study goes one step further in that it shows that rules seem to govern the relative completeness of song imitations. Incomplete imitations are more common among early-hatched than amo0ng late-hatched siblings. Moreover, the completeness of the imitation seems to be influenced by the order of song development, which tends to be inversely related to hatching order. A simple explanation for all of the facts we observed is that model abundance affects the fidelity of imitation. Fidelity is at its peak when there is a single model source-in-our case the father-and a single, live-in-pupil that imitates the model. However, factors other than model abundance alone could also affect the completeness of song imitation. Future studies could be developed to determine the effects of these other factors. Bohner, J. (1983) Anim Behav.31, 231-237.