Br. Coppedge et al., AGONISTIC BEHAVIOR ASSOCIATED WITH ORPHAN BISON (BISON-BISON L.) CALVES RELEASED INTO A MIXED RESIDENT POPULATION, Applied animal behaviour science, 55(1-2), 1997, pp. 1-10
Aggressive interactions of 43 bison (Bison bison L.) calves (10 months
old) released motherless into a 288-member resident bison population
of mixed composition were observed. Based on expected observations of
aggressive interactions from chi(2) analyses, these 'orphan' calves we
re recipients of significantly more aggression than any resident age c
lass, including similarly aged resident calves. Most aggression direct
ed towards orphans was initiated by resident yearlings. We did not obs
erve orphan calves initiate any aggression towards other animals durin
g the study, even towards other orphans. These findings support previo
usly suggested hypotheses that: (1) dominance rank in bison is linear
and established by older cohorts over each subsequent year's cohort; a
nd (2) maternal presence is socially beneficial to young bison by redu
cing aggression directed towards the offspring from other herd members
and facilitating their social integration. Surprisingly, no differenc
es were found in growth rates between orphan calves and resident calve
s with mothers, despite initial weight differences that were significa
nt. This finding suggests that the higher levels of hostility experien
ced by the orphan calves had no significant physical effects. (C) 1997
Elsevier Science B.V.