Male Group Dynamics and Inter?male Aggression of Guanacos in Southern Chile

Group dynamics and aggressive behavior of guanaco (Lama guanicoe) male groups (MGs) were described and quantified. All?male groups consisted of yearling, subadult, and adult males. Yearlings joined MGs from early Sep. to Feb., but the majority entered groups in Dec. and Jan. Adult males dispersed from MGs in Jan. and Feb. to establish or challenge tor territories. Young females were occasionally observed in MGs, but not during the height of the breeding season. Aggressive activity rates peaked in Jan., and older males were more aggressively active than younger males, initiating more threats and receiving fewer. After the breeding season, rates of aggression decreased but mean durations of two ear threats increased, suggesting that threats may replace energetically costly fighting as a sign of increased aggressiveness. Guanaco fighting style was similar to that of Equidae, in that fights proceeded in an unpredictable manner to unbalance and bite the opponent. The guanaco chest?ram was hypothesized to be a ritualized behavior that coevolved with the large camelid canine teeth. Male guanacos spend 3-4 years in all?male groups where they assess size and fighting ability via chest?rams and playfighting, thus presumably improving fighting skills that may ultimately affect reproductive success. Comparisons with horned ungulates are also discussed.