Vocal syntax development in the white-crowned sparrow (Zonotrichia leucophrys).

Birdsong development exemplifies the interplay between experience and predisposition that occurs during behavioral ontogeny. Songbirds must hear song models to develop normal song, yet they preferentially learn conspecific song when given a choice in the laboratory. To the extent that features guiding this selective learning are pre-encoded in the brain, such features should also develop in the song of young birds not exposed to them in tutor models. To investigate whether song syntax-phrase number and order--is such a feature in the white-crowned sparrow (Zonotrichia leucophrys), the authors tutored males of this species with separate phrase models. Birds learned and assembled these into songs of species-typical sequence, suggesting that syntax is to some degree pre-encoded in white-crowned sparrows. Birds also learned heterospecific phrases, confirming previous evidence that note phonology is not the primary cue for selective song learning in this species.

Acoustic and neural bases for innate recognition of song.

In behavior reminiscent of the responsiveness of human infants to speech, young songbirds innately recognize and prefer to learn the songs of their own species. The acoustic and physiological bases for innate recognition were investigated in fledgling white-crowned sparrows lacking song experience. A behavioral test revealed that the complete conspecific song was not essential for innate recognition: songs composed of single white-crowned sparrow phrases and songs played in reverse elicited vocal responses as strongly as did normal song. In all cases, these responses surpassed those to other species' songs. Although auditory neurons in the song nucleus HVc and the underlying neostriatum of fledglings did not prefer conspecific song over foreign song, some neurons responded strongly to particular phrase types characteristic of white-crowned sparrows and, thus, could contribute to innate song recognition.

Development of the catecholaminergic innervation of the song system of the male zebra finch.

Catecholamines (CA) have been proposed to have neuromodulatory actions, particularly on attention and learning, in a number of neural systems. Because several of the interconnected brain nuclei that mediate song learning and production in the adult male zebra finch (Taeniopygia guttata) contain these neurotransmitters, we investigated the appearance of the catecholaminergic innervation of the song nuclei of male zebra finches during posthatch development, specifically during the period in which song learning occurs. We studied the development of immunoreactivity for tyrosine hydroxylase (TH) in the song nuclei HVc, RA, NIf, LMAN, and Area X in young males aged 20, 35, and 60 days as well as in adults (> 90 days). We also visualized catecholamines directly in Area X using CA histofluorescence. Both TH immunoreactivity and CA histofluorescence were initially low in Area X relative to their levels in the surrounding parolfactory lobe (LPO), and then increased during development to become more intense than in LPO by days 60-90. Similarly, TH immunoreactivity in HVc was initially low relative to that in the surrounding neostriatum, then increased during development to become more intense than that in the surround by day 60. TH immunostaining also increased markedly in NIf, RA, and LMAN over the same period. These results show that the levels of catecholamines and their major synthetic enzyme increase in song nuclei during development and thus raise the possibility that these transmitters contribute to the development of the song system or to song learning.