The Annual Cycle of White-Crowned Sparrows (Zonotrichia leucophrys nuttalli) in Coastal California

Abstract

The basic unit of temporal organization in long-lived animals is the annual cycle, In birds this includes most prominently the periods of winter maintenance, reproduction, molt, and migration or dispersal. To attain maximal, or at least adequate, fitness, all of these essential processes must occur and be timed in individuals and populations so that conflicting demands for time and energy are minimized and they must exploit as well as possible the cyclic variations of the environment. The structure of the annual cycle thus represents evolutionary tendencies toward optimization, including, for instance, the length of the reproductive period, the pattern and duration of molt, and the proclivity for migration. Although much can be learned about the adaptive basis of the annual cycle by intensive investigation of individual taxa or geographic populations, much more can be learned by comparisons of taxonomic or geographic variants. Through nearly four decades of research, beginning with the pioneering investigations by Blanchard (summarized by DeWolfe 196S), the annual cycles of the crowned sparrows, Zonotrichia spp., have been analyzed especially thoroughly in this context. It is paradoxical that certain aspects of the annual cycle and general biology are least well known in the form of Zonotrichia Zeucophrys that is most readily accessible from urban and academic centers. 2. 1. nuttalli, hereafter called Nuttall’ s Sparrow, is the only nonmigratory form of Zonotrichia in North America, and is thus of particular interest in a comparative context. Nuttall’ s Sparrow inhabits the narrow coastal fog zone of California between about 34” and 40” N latitude. We report below the results of a five-year investigation of the cycles of reproduction and molt in Nuttall’ s Sparrows on Point Reyes, near the middle of their latitudinal range.