Scent marking in a territorial African antelope: II. The economics of marking with faeces

Faeces may be ideal substances for scent marking because they have a minimal energetic cost to the signaller. However, marking with faeces is also constrained by the animal's ability to produce faeces. This study examined whether limits on the volume of faeces produced by oribi, Ourebia ourebi, in Serengeti National Park, Tanzania, caused territorial males to regulate their output and prioritize the placement of faecal marks. Territorial males marked with faeces more often, and with a smaller volume per defecation, than did juvenile males and females. Territorial males also defecated only on established dung middens along borders shared with other territorial males or on top of a female's urine and faeces. In contrast, juvenile males and females defecated randomly with regard to their location in territories. Territorial males with larger harems marked with faeces at higher rates and less volume than males with few or no females. This difference suggests that when males overmark female excretions they reduce the amount of faeces available for marking other preferred sites, such as along territory borders shared with other males. Dominant males with adult subordinates marked with faeces less often, and with a greater volume per mark, than males that defended territories without the aid of subordinates. Dominant males also reduced the volume of marks less as the number of females on their territory increased than did males without subordinates. Territories occupied by more than one adult male also were marked with faeces at higher rates, and with marks of greater volume, than territories held by single males. These results suggest that the presence of subordinate males reduced the demand on dominant males to, regulate the volume and placement of faecal marks. Overall, these results suggest that territorial male oribi;regulate their faecal marking behaviour in response to a limited supply of faeces. (C) 1999 The Association for the Study of Animal Behaviour.