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 minima l energetic cost to the signaller. However, marking with faeces is also con strained by the animal's ability to produce faeces. This study examined whe ther limits on the volume of faeces produced by oribi, Ourebia ourebi, in S erengeti National Park, Tanzania, caused territorial males to regulate thei r output and prioritize the placement of faecal marks. Territorial males ma rked with faeces more often, and with a smaller volume per defecation, than did juvenile males and females. Territorial males also defecated only on e stablished dung middens along borders shared with other territorial males o r on top of a female's urine and faeces. In contrast, juvenile males and fe males defecated randomly with regard to their location in territories. Terr itorial males with larger harems marked with faeces at higher rates and les s volume than males with few or no females. This difference suggests that w hen males overmark female excretions they reduce the amount of faeces avail able for marking other preferred sites, such as along territory borders sha red with other males. Dominant males with adult subordinates marked with fa eces less often, and with a greater volume per mark, than males that defend ed territories without the aid of subordinates. Dominant males also reduced the volume of marks less as the number of females on their territory incre ased than did males without subordinates. Territories occupied by more than one adult male also were marked with faeces at higher rates, and with mark s of greater volume, than territories held by single males. These results s uggest that the presence of subordinate males reduced the demand on dominan t males to, regulate the volume and placement of faecal marks. Overall, the se results suggest that territorial male oribi;regulate their faecal markin g behaviour in response to a limited supply of faeces. (C) 1999 The Associa tion for the Study of Animal Behaviour.