Dominant Red Junglefowl (Gallus Gallus) Hens in an Unconfined Flock Rear the Most Young over Their Lifetime

Abstract

-The evolutionary success of individuals must ultimately be evaluated in terms of their lifetime contribution of mature young to the breeding population. The greater lifetime breeding success of the more dominant hens in an unconfined flock of Red Junglefowl (Gallus gallus) gave crucial evidence why female dominance hierarchies have evolved in this species. The number of chicks reared to independence by 28 hens of one flock from 1982 to 1988 was significantly associated with a hen's dominance, life-span, and year of hatching. Of these, dominance was by far the most important factor. It, by itself, could explain differences in the number of chicks reared as shown by log-linear analysis. This suggests that the associations with life-span and year of hatching may result from the fact that these are correlated with dominance. The top 3 hens in the peck order added more offspring of breeding age to the population than did the remaining 25 adult hens of the flock. Eleven of the 28 hens reared no young successfully. Received 8 March 1993, accepted 2 July 1993. THE DIFFERENT INDIVIDUALS in a natural population vary greatly in the numbers of young that they manage to rear successfully, with profound implications for population dynamics and evolution. The purpose of this report is to identify and evaluate some of the important factors that account for this difference among individuals in an unconfined population of Red Junglefowl (Gallus gallus), taking into account differences in life-span, age class (year of hatching), and lifetime dominance status of adult hens. Darwin (1887, vol. 1:258) concluded that the Red Junglefowl was the ancestor of the domestic fowl, and much recent evidence accumulated since then has tended to confirm his view (Delacour 1977, Crawford 1990, Stevens 1991). Not all breeds of domestic fowl have been thoroughly investigated from this viewpoint, and it is still considered possible that genes from other species of junglefowl might have been introduced by hybridization in some breeds (Crawford 1990, Stevens 1991). The Red Junglefowl has the special advantage that one may be able to relate behavioral observations to the vast amount of work that has been done on the behavior, physiology, and genetics of domestic fowl. A field study of the behavior of Red Junglefowl in India (Collias and Collias 1967) and a parallel study of an unconfined population at the San Diego Zoo (Collias et al. 1966) showed that the behavior of the birds and the social structure of the population, aside from greater dispersion in nature, were basically and qualitatively similar in the two places. The Red Junglefowl is much hunted by humans and is one of the most wary of game birds (Bump and Bohl 1961). We returned to the zoo population for information on details of behavior of individuals over the adult life-span. This information would have been exceedingly difficult to obtain in the wild, and we feel that the observations on the zoo population generally will be found to apply in the field. We hope that the zoo studies will stimulate and provide some guidance for future studies under the more difficult field conditions. The evolutionary significance of individuals ultimately must be evaluated in terms of their lifetime reproductive success in the population. In recent years there has been an increasing emphasis on the study of lifetime reproductive success in birds. A recent review volume (Newton 1989) summarized long-term studies on 23 species of birds. Despite great differences in body size and life history, in all of these species breeding life-span emerged as the major demographic determinant of lifetime reproductive success when measured as fledgling production. However, where lifetime reproductive success was measured by the number of recruits to local breeding populations rather than by the number of fledglings, life-span contributed much less to variance in lifetime reproductive