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

Abstract

Nuttall''s sparrow [Z. l. nuttalli] is a nonmigratory form of white-crowned sparrow that inhabits the Mediterranean plant community of the coastal fog zone of California [USA]. The major events of its annual cycle were investigated through 5 consecutive seasons near the middle of its latitudinal range in Marin County. The nesting season, following a sparse prenuptial molt lasting about 60 days, begins in late March and continues for about 125 days. Indirect evidence (brood-patch condition) indicates that most females incubate 2 broods per nesting season and some incubate 3. A small minority apparently incubates only 1 brood. Postnuptial molt requires 68 days on the average, and is temporarily suspended in a small fraction of individuals late in the season. Postjuvenal molt begins about 20 days after the juvenal plumage has finished growing, and requires about 60 days on the average. Body weight in both adults and young undergoes an annual cycle having a maximum in midwinter and a minimum in midsummer. Much weight is added during the postnuptial molt, and a lesser amount during the prenuptial molt. During the investigation, the phase of the annual cycle with respect to calendar date varied about .+-. 15 days from the median, delay being correlated with cold and (or) rainy weather during the prenesting period (but not correlated with weather during other phases of the annual cycle). Nuttall''s sparrow invests about 1/3 of the year in reproduction, 1/3 in molt and 1/3 in winter maintenance.