During the breeding season, the males of various animal species will devote many long hours to closely following and protecting their mate, a behaviour that is known as “mate-guarding”. They do this to prevent rival males from accessing their partner and in doing so, are able to guarantee that they will be the father of her offspring.
Despite the obvious benefits to the male, this close monitoring of the female’s movements can prove to be extremely taxing. In rhesus macaques (Macaca mulatta), the males usually store extra fat reserves in anticipation of this extra activity. By the end of the mating season, mate-guarding males will have lost much of their weight and will be in poor physical condition. But for other species this burden is not so costly. To discover why this is so, researchers monitored the behaviour of another species of macaque, the long-tailed macaque (Macaca fascicularis) from the Gunung Leuser National Park in Indonesia.
These long-tailed macaques lived in social groups of up to 58 individuals. Although female long-tailed macaques can conceive at any time of the year, their reproductive cycle usually coincides with periods of maximum fruit availability. This lack of seasonality enabled researchers to follow the macaques for two distinct 5-month mating periods within a single year. They spent hundreds of hours in the primary lowland rainforest trailing after the macaques, recording every movement of the males, how often they fed and the distances that they travelled.
Males were found to guard females for an average of four consecutive days, devoting approximately 30% of their time to this activity. They did this at the expense of their own feeding time and had a greatly restricted diet, feeding on fewer fruits than they normally would. This equated to a considerable reduction in energy intake for the males, yet to the surprise of the researchers, this did not appear to affect their overall energy levels.
Instead they found that the macaques were able to compensate for any reduced food consumption by moderating their physical activity – they no longer climbed as much, and so saved themselves a tremendous amount of energy. These results show that under certain circumstances, males may be able to maintain their strength even when actively protecting a female over several days. However, further investigations will be needed to show if this also occurs in other mate-guarding species.
Reference: Girard-Buttoz, C., Heistermann, M., Rahmi, E., Marzec, A., Agil, M., Fauzan, P., & Engelhardt, A. (2014). Mate-guarding constrains feeding activity but not energetic status of wild male long-tailed macaques (Macaca fascicularis) Behavioral Ecology and Sociobiology DOI: 10.1007/s00265-013-1673-8
Image: Terry Townshend