Syllable repertoire and the size of the song control system in captive canaries (Serinus canaria).

In songbirds, there is considerable interest in relationships between song structure and the size of the song control system in the forebrain. In male canaries, earlier studies have reported that repertoire size increased with age, and positive correlations were obtained between repertoire size and the volume of song control nuclei such as high vocal center (HVC). Here we investigate whether age has an effect upon both the song structure and the morphology of two song control nuclei [HVC and robustus archistriatalis (RA)] that are important in song production. We recorded songs from an aviary population of 1- and 2-year-old male domesticated canaries. We found that repertoire size, number of sexually attractive (sexy) syllables, and size of song nuclei did not differ between 1- and 2-year-old males. Neither did we find significant correlations between syllable repertoire size and the size of the song control nuclei. However, HVC size was positively correlated with the proportion of sexy syllables in the repertoires of 2-year-old males. Some older males may enhance vocal performance by modifying the control of syllables rather than by increasing repertoire size or neural space.

Leitner S ，Catchpole CK 《journal of neurobiology》

Female canaries that respond and discriminate more between male songs of different quality have a larger song control nucleus (HVC) in the brain.

In male songbirds the song control pathway in the forebrain is responsible for song production and learning. In most species, females do not sing and have smaller nuclei in the song control pathway. Although the function of the pathway in females is assumed to be associated with the perception of male song, there is little direct evidence to support this view. In this study on female canaries, we investigate the role of two key nuclei in the song control pathway (HVC and lMAN) in relation to playback of male song. Male canaries produce elaborate songs that function to attract and stimulate females. The songs are constructed from smaller units called syllables, and special syllables with a more complex structure (sexy syllables) are known to induce females to perform copulation solicitation displays (CSD) as an invitation to mate. By using computer-edited experimental songs, we first show that females discriminate between songs by producing significantly more CSD to those containing sexy syllables. We then sectioned the brains and used in situ hybridization to reveal song nuclei containing androgen receptors. We report positive correlations between the size of HVC and both total CSD response and the amount of discrimination between sexy and nonsexy songs. We found no such relationships between these measures and the size of lMAN. These results provide some evidence to support the view that, in female canaries HVC is involved in female perception and discrimination of male song. The results also have implications for the evolution of complex male songs by sexual selection and female choice.

Leitner S ，Catchpole CK 《journal of neurobiology》

Song and brain development in canaries raised under different conditions of acoustic and social isolation over two years.

Early isolation experiments indicate that male songbirds learn their songs during an early sensitive period, although later work has shown that some open-ended learners modify songs in later years. Recent isolation experiments suggest that in some species song has a stronger genetic basis than previously thought. This study raised domestic canaries under different combinations of acoustic and social isolation and followed song development into the second year. Males raised alone in acoustic isolation developed songs with normal syllables, but larger repertoires and also produced syllables with lower repetition rates when compared to controls. The smallest repertoire occurred in males raised in a peer group. Isolate males had a smaller song control nucleus HVC than controls, but there was no effect on nucleus RA or on brain weight in general. In the second year, after introduction into a large normal colony, isolate and peer group males adjusted their syllable repertoire to normal size. In particular, the isolates reduced their repertoire even though the size of HVC showed a significant increase in volume. However, songs of isolate and peer group males still differ in repetition rate and number of single syllables in the common aviary. In contrast, control males showed low syllable turnover and no significant change in repertoire size. Nor did they show any significant change in the volumes of song control nuclei. It seems that complete isolation affects only some aspects of song and brain development, and later socialization corrects some but not all of these in the second year.

Leitner S ，Catchpole CK 《Developmental Neurobiology》

Seasonal activation and inactivation of song motor memories in wild canaries is not reflected in neuroanatomical changes of forebrain song areas.

Seasonal, testosterone-dependent changes in sexual behaviors are common in male vertebrates. In songbirds such seasonal changes occur in a learned behavior--singing. Domesticated male canaries (Serinus canaria) appear to lose song units (syllables) after the breeding season and learn new ones until the next breeding season. Here we demonstrate in a longitudinal field study of individual, free-living nondomesticated (wild) canaries (S. canaria) a different mode of seasonal behavioral plasticity, seasonal activation, and inactivation of auditory-motor memories. The song repertoire composition of wild canaries changes seasonally: about 25% of the syllables are sung seasonally; the remainder occur year-round, despite seasonal changes in the temporal patterns of song. In the breeding season, males sing an increased number of fast frequency-modulated syllables, which are sexually attractive for females, in correlation with seasonally increased testosterone levels. About 50% of the syllables that were lost after one breeding season reappear in the following breeding season. Furthermore, some identical syllable sequences are reactivated on an annual basis. The seasonal plasticity in vocal behavior occurred despite the gross anatomical and ultrastructural stability of the forebrain song control areas HVc and RA that are involved in syllable motor control.

Leitner S ，Voigt C ，Garcia-Segura LM ，Van't Hof T ，Gahr M ... -  《HORMONES AND BEHAVIOR》

Social context affects testosterone-induced singing and the volume of song control nuclei in male canaries (Serinus canaria).

Boseret G ，Carere C ，Ball GF ，Balthazart J ... -  《journal of neurobiology》