SEASONAL PLASTICITY OF THE SONG CONTROL-SYSTEM IN WILD NUTTALLS WHITE-CROWNED SPARROWS

Seasonal plasticity in the morphology of telencephalic nuclei that con trol song behavior has been reported for diverse species of songbirds, The only published report of a lack of seasonal changes in the song n uclei of a seasonally breeding bird is that of Baker et al, in the Nut tall's subspecies of white-crowned sparrow (Zonotrichia leucophrys nut talli). In this study, they brought wild birds into the laboratory and exposed them to either ''summer'' or ''winter'' photoperiods, Previou s 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 breed ing birds, Changes in circulating T are primarily responsible for the seasonal morphological changes in the song nuclei, To determine whethe r 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 th e spring and fall, Testis size and circulating T concentrations were g reater in spring than fan birds, The absolute volumes of the song nucl ei HVc, RA, and Area X, and their volumes relative to those of either the total telencephalon or three thalamic nonsong nuclei, were signifi cantly greater in the spring than fall sparrows. Song behavior also ch anged seasonally; fall birds sang shorter songs than did spring birds, These results show that there is seasonal plasticity of the song syst em in wild Nuttall's white-crowned sparrows, Seasonal plasticity can n ow be regarded as a common feature of the seasonally breeding songbird s studied thus far. (C) 1998 John Wiley & Sons, Inc.