Diversity in Two Wintering Bird Communities: Possible Weather Effects

Abstract

THE study of bird species diversity has thus far been concerned primarily with nesting bird communities (MacArthur and MacArthur 1961, Karr 1968, Recher 1969, Kricher 1973). Comparable studies on winter bird communities are less frequent (but see Emlen 1972, Austin and Smith 1972). This is unfortunate because winter presents a very distinct series of stresses to avian populations, differing from those of the nesting season. In winter, birds in north temperate latitudes are concerned only with individual survival. There is no singing, courtship display, or nesting activities. Acquisition of food is of prime importance to birds occupying a winter environment characterized by short daylight hours and an ambient temperature usually many degrees below body temperature (Gordon et al. 1968). Migration testifies to the rigors of the temperate winter environment. Recent studies of avian population biology (Lack 1966, 1968; Fretwell 1969, 1972) emphasized the possible importance of the winter season as a regulator of population size. The objective of this paper is to examine the patterns of winter bird species diversity over a 2-year period in two ecosystems of the New Jersey Piedmont. Considerable attention has been paid to possible relationships between weather factors and avian population and diversity changes. It is hoped that the elucidation of patterns in winter bird species diversity will contribute a greater understanding to the importance of the winter season relative to population regulation and will also contribute to an increased understanding of how ecosystems function.