Colour signals arise in a variety of sexual contexts, including advertising reproductive status. Despite potentially attracting negative attention from unrelated competitors, bright pregnancy coloration may communicate gestation to kin and potential fathers, thereby garnering aid during agonistic encounters and reducing the overall amount of aggression received by pregnant females. To establish whether this 'pregnancy sign' influences rates of aggression in the presence versus absence of maternal kin, we conducted behavioural observations of wild olive baboons, Papio anubis, in Gombe National Park, Tanzania, in groups composed of maternal kin and nonkin, and of captive baboons at the Southwest National Primate Research Center (SNPRC, San Antonio, TX, U.S.A.), in group enclosures that were unlikely to include close kin. At SNPRC, we also experimentally obscured the coloration of the pregnancy sign, and we performed playback experiments to measure male responses to the distress calls of pregnant females. Free-ranging female baboons experienced significantly less aggression from nonkin females after the onset of the pregnancy sign compared to the pre-pregnancy sign. In contrast, captive pregnant females whose pregnancy coloration was obscured with paint experienced significantly lower aggression rates from female conspecifics compared to pre-painting. Male aggression towards females did not differ in the presence versus absence of the pregnancy sign in either the wild or the captive population, although captive fathers paid significantly more attention to distress calls of pregnant cage-mates than they did to those of cycling cage-mates, suggesting a willingness to aid mothers that were carrying their unborn offspring.
Bibliographical noteFunding Information:
We gratefully acknowledge the financial support provided by the American Society of Mammologists, the American Society of Naturalists, the Animal Behavior Society, the Dayton Bell Museum Fund Fellowship, the National Science Foundation Graduate Research Fellowship Program and the Wenner-Gren Foundation (grant number 8474 ). We thank the Tanzania Wildlife Research Institute (TAWIRI) and the Tanzania National Parks for permission to work in Gombe National Park, and the Jane Goodall Institute and Gombe Stream Research Center for allowing us access to their infrastructure and facilities. Special thanks go to the Gombe field assistants who aided in the collection of this data, especially Hamimu Mbwama. We also thank the Southwest National Primate Research Center for granting us access to their facility, with a special thanks to the staff for their expertise and help. Finally, we thank Emily Briggs and Katie Gundle for their work coding the vocalization playback videos and Dr Michael Wilson for his advice and support.
- Olive baboon
- Papio anubis
- Pregnancy sign