Group composition in wild and commensal hamadryas baboons: A comparative study in Saudi Arabia

Papio hamadryas was surveyed throughout its range in Saudi Arabia and was observed at altitudes ranging from 0 to 2300 m. Wild populations occur along the whole range of altitude, while commensal populations are only found above 850 m altitude. No variation in group size was found with altitude. Comparison of wild and commensal populations showed the following. (1) Their composition in terms of age and sex classes, overall adult sex ratios, and group size does not significantly differ. (2) Groups of both populations include, in similar proportions, three types of parties: one-male units (>70%), two-male units (>13%), and a few other units of variable composition. (3) The mean size of commensal parties is significantly larger than in the wild population; specifically one-male units are larger in the commensal population due to a larger number of females per male. Thus, female distribution in commensal groups is more inequitable than that in wild groups. (4) Finally, the number of females included in two-male units increases with altitude. These differences are discussed in terms of food availability and predator pressure and are compared with results obtained on other Arabian and Ethiopian populations.