Distribution and Dispersal of the Cardinal, Richmondena cardinalis, in Relation to Vegetational Cover and River Systems

Abstract

Cardinals, Richmondena cardinalis, were studied at four locations of different population density to determine if their presence was correlated with certain environmental features. Distributional data were based on responses to tape-recorded cardinal song, and relationships were analyzed using linear regression techniques. An increase in woody cover, regardless of foliage type, was associated with an increase in cardinal numbers in all regions, but cardinals occupied even very sparse cover in Tennessee. A strong association with river systems noted in peripheral populations was not displayed by cardinals in the center of their range, and largely coniferous vegetation close to these rivers in any region did not appear to deter them. The edge of the cardinal's range in Ontario shows good agreement with snowfall distribution peculiar to the region. It is suggested that most dispersal is effected by young cardinals using rivers as guidelines and thus settling close to them through inertia, and not because they offer the best available habitat. The cardinal's northward spread is likely limited by winter snow cover and concomitant food shortage rather than by unsuitable vegetation. INTRODUCTION The cardinal, Richmondena cardinalis, is characteristic of the avifauna of the Carolinian Zone or Deciduous Forest Biome, and provides perhaps the classic example in North America of the rapid range expansion possible among indigenous birds. The euryoecious distribution of a dense Tennessee population suggests that foliage type and even amount of vegetational cover may be of little importance to cardinals, and need only provide adequate nest-sites (Dow, 1969a,b). Observations of cardinals living in cypress cedar swamps, spruce and pine plantations, or other coniferous situations in various parts of their range, suggest that even relatively homogeneous tracts of boreal forest vegetation might be insufficient to limit their northward expansion. The cardinal first bred in southern Ontario in 1901 (Snyder, 1957), and from that time its history has been well documented. Snyder (1957) and De Vos (1964) have speculated on factors responsible for the rapid spread of the species in Ontario. The present paper examines some factors possibly limiting its distribution, particularly foliage types and amounts of woody vegetation, river systems, and snowfall. METHODS Between 1965 and 1967 I studied populations of cardinals at four locations, one of high density near the town of Dresden in western 1 Present address: Department of Zoology, University of Queensland, St. Lucia, Brisbane, Australia.