Photoperiod and tutor access affect the process of vocal learning.

Song learning in white-crowned sparrows, Zonotrichia leucophrys, involves three steps: memorization of external models, song practice and selection of a song from the practiced repertoire for crystallization. These three events occur in a sequential and predictable order during the first year of life in captive sparrows. To study the external regulation of these events, we raised nestling sparrows under conditions in which photoperiod and tutor exposure were manipulated.

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.

Testosterone-induced shortening of the storage phase of song development in birds interferes with vocal learning.

Bird song is a complex, learned behavior. Vocal learning in sparrows involves several different processes that occur in a distinct temporal pattern over the course of the first year of life. Songs are acquired without practice during a sensitive period within the first 3 months of life and rehearsal of the acquired song does not begin until 7 or 8 months of age.

Sustained hormonal responses of Siberian hamsters (Phodopus sungorus) to a single longer day at weaning.

Siberian hamsters undergo gonadal development for several weeks after exposure to a single longer day at weaning. To characterize changes in gonadotropin secretion after a single acute light stimulus, hamsters housed in a long photoperiod (16L:8D) were given a single longer day (20L:4D) or maintained in the 16L:8D photoperiod at 19 days of age and transferred to a short photoperiod (8L:16D) on Day 20. Elevated plasma FSH concentrations were detected in male hamsters at 5, 7, and 12 but not at 17 days after the single longer day.

Long day lengths enhance myelination of midbrain and hindbrain regions of developing meadow voles.

Rates of brain growth differed in meadow voles maintained in long (LP) or short (SP) photoperiods postnatally. At 35 days of age, brain weight was greater by 6.6% in LP males and by 4.