Population Variabilities of Bird Guilds in Kansas during Fall and Winter: Weekly Censuses versus Christmas Bird Counts

Abstract

Fall and winter (September through March) weekly census data from 1978 through 1992 were examined for 18 species of birds in forests and cultivated fields near Manhattan, Kansas. The 18 species were grouped into five feeding guilds: frugivores; granivores on the ground; acorn cachers; leaf, bud, and twig gleaners; and trunk and branch gleaners. Frugivores exhibited the most variable populations, both within years and between consecutive years. Granivores on the ground exhibited the second most within-year population variability. Among the remaining guilds, there were no statistically significant differences among either the within- or between-year variabilities. Although data were limited, there were significant correlations between the mean numbers in some species of frugivores, granivores, and acorn cachers and relative annual fruit or seed crop size in the area. The size and mobility of feeding flocks, the annual variability of food crops, and the manner of food exploitation all influenced the between-year variability of winter bird species population density. The rank order of between-year variability for species populations censused on Christmas Bird Counts in the same area correlated significantly with between-year variability of our weekly censuses. The within-year nomadic tendencies of some of the species with the greatest between-year variability decreased the correlation between Christmas Bird Counts and mean weekly censuses for these species.