Demographic Patterns of the Vinous-Throated Parrotbill

Abstract

The vinous-throated parrotbill is one of the most widely distributed bird species in Taiwan and has a wide niche. To understand the population parameters of this highly social species, I monitored several parrotbill flocks from July 1983 through August 1990 on the Tunghai University Campus, Taichung, Taiwan. An effort was made to keep at least 80% of the population color-marked for individual identification throughout the study. The mean clutch size was 4.01 eggs (N=14O nests). The incubation period was 14 days, and nestling period 14 days. The mean hatching success was 2.68 eggs per nest (0.64 per egg). The mean fledging success was 1.90 young per nest (0.74 young per hatchling). Both sexes became sexually mature at one year and breeding was monogamous. Because parrotbill flocks utilize very dense vegetation, it was not always possible to identify all the birds present in each flock. The survival rate of the different cohorts was obtained. Mortality varied with age, being low in the third year, and high after the fourth year. When parrotbill flocks encountered each other, some birds changed flocks. The ratio and pattern of flock change was analyzed as an index for the rate of emigration and immigration. Age composition of each flock was analyzed by using banding dates as an index of age. There was remarkable similarity between the age composition of different flocks within a year but age composition of the population differed between years. The size of this population remained relatively stable before large scale habitat destruction began. With the shrinking of usable habitat within the study area, the population size declined slowly and the affected flocks increased the amount of time they spent outside the study area. However, the decline was offset by influx of birds from nearby areas where habitat also decreased.