Seasonal plasticity of the song control system in wild Nuttall's white-crowned sparrows

Abstract

Seasonal plasticity in the morphology of telencephalic nuclei that control song behavior has been reported for diverse species of songbirds. The only published report of a lack of seasonal changes in the song nuclei of a seasonally breeding bird is that of Baker et al. in the Nuttall's subspecies of white‐crowned sparrow (Zonotrichia leucophrys nuttalli) . In this study, they brought wild birds into the laboratory and exposed them to either “summer” or “winter” photoperiods. Previous studies have shown that exposing wild‐caught white‐crowned sparrows to long‐day photoperiods in the laboratory may not induce circulating concentrations of testosterone (T) as high as those seen in wild breeding birds. Changes in circulating T are primarily responsible for the seasonal morphological changes in the song nuclei. To determine whether there is seasonal plasticity of the song system in this subspecies, we measured circulating T, morphological attributes of the song nuclei, and song behavior in wild Nuttall's white‐crowned sparrows during the spring and fall. Testis size and circulating T concentrations were greater in spring than fall birds. The absolute volumes of the song nuclei HVc, RA, and Area X, and their volumes relative to those of either the total telencephalon or three thalamic nonsong nuclei, were significantly greater in the spring than fall sparrows. Song behavior also changed seasonally; fall birds sang shorter songs than did spring birds. These results show that there is seasonal plasticity of the song system in wild Nuttall's white‐crowned sparrows. Seasonal plasticity can now be regarded as a common feature of the seasonally breeding songbirds studied thus far. © 1998 John Wiley & Sons, Inc. J Neurobiol 34: 69–82, 1998

Structural Changes between Seasons in the Songbird Auditory Forebrain

“…The telencephalon size of songbirds in different seasons has already been reported (Smith, 1996;Brenowitz et al, 1998) but without significant differences. Because it allows to search for volume changes at the intraindividual level, repeated measures MRI is statistically more powerful than histology for identifying small but real differences in volumes, explaining why other studies may have failed to identify this telencephalon volume change.…”

Plasticity of the Avian Song Control System in Response to Localized Environmental Cues in an Equatorial Songbird

“…Brain sectioning and Nissl staining were always done on pairs of brains, one from each population. Song nuclei volumes were measured and calculated as described previously (Smith et al, 1995;Brenowitz et al, 1998;Tramontin et al, 1998). Briefly, a magnified (46ϫ) image of each stained section was projected onto paper, and the profiles of the telencephalic song nuclei HVC, RA, and X were traced.…”

Seasonal neuroplasticity in the songbird telencephalon: A role for melatonin

“…It must be noted that these centrally mediated different reproductive states are not mediated by seasonal changes in gonadal steroids and still occur at the levels of the hypothalamus and the pituitary gland, even in the absence of gonads (2). Coincident with changes in reproductive activity, seasonal neuroplasticity now documented in several species of oscine songbirds occurs within discrete telencephalic nuclei that are involved in song learning and production (3)(4)(5)(6)(7). Increases in the volumes of these song-control nuclei largely depend on seasonal increases in circulating testosterone (T) and its metabolites (8)(9)(10) that are directly related to the annual reproductive cycles of these birds (11).…”