Temporal stability and change in a microgeographical pattern of song variation in the rufous-collared sparrow

摘要

We studied the pattern of song variation in the rufous-collared sparrow, Zonotrichia capensis, in the 1987 and 2000 breeding seasons in a 7-km~2 area covering open and closed habitats. We measured 14 quantitative song variables over a total of 390 individuals and found consistent differences between habitats in both years. In particular, songs of individuals from closed habitat sites had trills with longer trill intervals and lower frequencies than those of individuals from open habitats. This pattern of variation is interpreted as a song cline that correlates with the environmental gradient. Although this cline was stable in location and shape, it also showed several differences between years. The songs recorded during 2000 had trills with longer trill intervals and lower minimum frequencies than those recorded during 1987. Thus, this study is the first to directly document temporal changes in song variables in a Z. capensis population. This change would be expected if all the habitats studied were more closed in 2000 than in 1987, but we did not find obvious differences in habitat features between seasons. However, this modification of song structure is compatible with alternative explanations, such as subtle differences in habitat characteristics, changes in climatic variables, a delayed effect of a past modification of the environment and neutrality of the change.