The Timing of Life-History Stages Across Latitudes in Zonotrichia Sparrows

Tropical vertebrates are considered to have greater flexibility in the timing of life-history stages than are temperate-zone vertebrates. Yet the annual cycles of most resident tropical species are poorly understood, making latitudinal comparisons of phenology difficult. We investigated the reproductive seasonality and synchrony of a mid-elevation (∼2100 m), equatorial population of the Rufous-collared Sparrow (Zonotrichia capensis) and compared our data with data from three other populations of Zonotrichia across a range of latitudes and elevations (one equatorial high-elevation population of Z. capensis and two temperate-zone populations of Z. leucophrys, one at high elevation and one at sea level). We predicted that (1) the reproductive synchrony and seasonality of temperate-zone populations should be greater than those of the equatorial populations and (2) the reproductive synchrony and seasonality of populations breeding at high elevations should be greater than those of populations breeding at lower elevations. We found no seasonal pattern in the proportion of adults' life-history stages in the mid-elevation equatorial population of Z. capensis. Broader comparisons revealed that the reproductive synchrony and seasonality of temperate-zone populations were not always higher than those of the equatorial populations. Elevation of the breeding population had a strong effect on reproductive seasonality in both temperate-zone and equatorial populations. However, reproductive synchronies of temperate-zone populations were very different, while those of equatorial populations were similar. Thus elevation and climatic factors associated with latitude of breeding are important to reproductive seasonality and synchrony.