Abstract - Mother-Daughter Interactions in American Bison (Bison bison): Factors Associated with Individual Variation

Green, Wendy Carroll Hortenstine. 1987. Mother-daughter interactions in American bison (Bison bison): Factors associated with individual variation. Ph.D. Dissertation. City University of New York. 202+ p.

Abstract

To describe developmental changes and individual variation in bison mother-daughter relations, I observed 13 dyads from birth to 1.5 years and collected supplementary data on the first five years for 48 daughters at Wind Cave National Park.

Pre-weaning spatial relations change minimally; mothers and calves follow each other infrequently and are often far apart. Bison appear to be neither hiders nor followers, but incorporate aspects of both strategies. Old and young mothers invest differently in offspring; while older cows provide more nursing care, young mothers contact calves more often. Maternal experience mitigates disruptive effects of tending by bulls on mother-calf relations.

Weaning occurs gradually, with little conflict. The end of weaning varies with the mother's subsequent reproductive status: pregnant cows stop nursing at 9-12 months; barren cows at 17-21. After weaning and the birth of the mother's next calf, daughters spend less time near mothers, but proximity-maintenance behaviors change little. While post-weaning associations with mothers vary in longevity, most continue at least until sexual maturity. Where bonds endure, mothers' efforts at proximity-maintenance are largely responsible.
Bison mother-daughter relationships appear to be polymorphic. Predominant classes reflect maternal and filial independence and maternal nursing tolerance. Bonds end earlier when mothers show aggression in the first few weeks and provide more nursing care. Filial and maternal independence are at opposite ends of a continuum. Calves are most independent when mothers maintain proximity often and nurse patiently.

Younger mothers and later-born calves behave as if to compensate for social and physical disadvantages. Late-born calves and their mothers synchronize movements more than other dyads. Young mothers have closer, longer-lasting relations with daughters. Larger daughters are born earlier, retain natal coats longer, achieve higher rank, and may calve earlier than smaller daughters; they are also more independent of mothers. Prolonged care by barren mothers enhances offspring size and, possibly, reproduction.
Dominance is correlated with age among cows, but with size and age among juveniles. Dominant cows tend to reproduce more than others and provide more nursing care; their daughters develop independence earlier and dominate peers. Dominance among daughters increases with nursing time and early independence.