Jan. 15 (UPI) -- Fewer than 10 percent of all mammals form pair relationships. For those that do, properly defining the nature of their relationship remains difficult. Are the animals true partners? Or do they simply share territory?
To better understand the characteristics of and motivations behind pair bonding, scientists closely monitored relationships among titi monkeys. The findings suggest females keep males around for protection and infant care.
"Our data is most consistent with the 'male-services' hypothesis for pair-bond maintenance, where a female contributes more to the proximity and affiliation maintenance while a male provides beneficial services," scientists wrote in their paper on the research, published Wednesday in the journal Royal Society Open Science.
For seven months, scientists with the German Primate Center, DPZ, observed seven groups of red titi monkeys in the Peruvian Amazon. The primates were used to the presence of humans. Researchers noted who sought proximity to its partner, who groomed whom and who engaged in confrontations with intruders.
"We have observed that the females, especially after giving birth, are increasingly concerned with maintaining relationships, i.e. actively seeking the proximity of their partner and grooming their fur," study author Sofya Dolotovskaya, doctoral student at the German Primate Center, said in a news release.
Meanwhile, the males were more likely to confront intruders and fend off rivals from his territory.
"This behavior is in line with the 'male-services hypothesis', which states that females are mainly concerned with being close to their partner while the latter provides useful services, such as defense against intruders or rearing the young," said DPZ researcher Eckhard W. Heymann.
The males don't just provide muscle. Researchers noted that male titi monkeys shoulder much of the parenting responsibility, carrying around their infants all day and returning them to their mother only to feed.
Researchers determined the partnerships are accompanied by monogamous mating behavior. Thus, male titi monkeys can spend more time and energy protecting their offspring, instead of concerning themselves with finding the next mate.
Previous research suggests dad's care likely provides offspring with benefits, too. One study found male parenting was associated with larger brain size.