How lion-tailed macaques have changed parenting techniques with rising rates of twins

Altruism is a much-debated topic in biological studies, and the prevailing conclusion is that almost all forms of altruism are reciprocal. “So, you’re either helping your kin, or you’re helping a friend who could potentially help you in the future,” says wildlife biologist Ashni Kumar Dhawale.

However, when Dhawale witnessed what seemed to be selfless altruism in the form of alloparenting or allomothering – where a non-related individual provides childcare – among the endangered lion-tailed macaques (Macaca silenus) in Puthuthottam in Tamil Nadu’s Valparai, it became the most incredible experience of her study.

Recounting the experience, Dhawale explains that she studied two mothers with surviving twins and their caretaking behaviour until the offspring turned one. This study was significant for two reasons: first, twins are an extremely rare occurrence among primates, especially lion-tailed macaques; second, the first year of an infant’s life is crucial for its survival, with mothers often investing heavily in their care until they pass this developmental milestone.

Alloparenting has not been observed in the species until now. “They have a long inter-birth interval of three years, so mothers are heavily invested in their infants,” says Dhawale. “This is evident in the way they care for them – they carry the infant and lactate for a year, which is not a common behaviour in mammals of that size, and not even among other primates.”

It takes a village

In the case of the Puthuthottam twins, when one mother faced the task of transporting her twins through a precarious location, she allowed an older female to carry one infant while she carried the other. The twins were in the latter half of their one-year development and were presumably too heavy for the mother to carry both at once.

Dhawale explains that this decision followed intense communication, during which the non-mother engaged in “affiliative behaviours” – friendly and peaceful acts such as lip-smacking and touching – to reassure the mother that the infant would be safe with her. Ultimately, the mother conceded. As soon as all four macaques had crossed the difficult path, the mother quickly retrieved her infant.

Dhawale believes this behaviour demonstrates the social intelligence of lion-tailed macaques and the cognitive processes involved. “There was nothing for the non-mother to gain from this act of helping. In fact, she risked being chased or even shown aggression by the mother, but she still approached and convinced her to let the infant go. In the end, the infants were safe,” she says.

Researchers have been studying the lion-tailed macaque population in Valparai and their adaptation to a human-modified landscape for over two decades. The forest in the region, located in the Anamalai Hills of the Western Ghats, is highly fragmented.

The paper notes that the Puthuthottam forest fragment currently supports a population of about 190 lion-tailed macaques, divided into five groups. The forest patch is less than one square kilometre in size and surrounded by tea plantations and adjacent to a town, pushing the growing macaque population to venture out of the forest fragment to explore the surrounding human-dominated landscape, where they exploit anthropogenic foods – primarily by foraging through garbage and entering homes.

The study observed several behaviour modifications among the mothers, who adjusted their actions to meet the needs of their twins. For instance, the mothers stayed closer to their infants while resting and foraging, rather than venturing closer to human settlements. As the twins grew in size, the mothers began spending more time on the ground and also socialised more with other adults and juveniles during this period.

The study also suggests that the rising rates of twinning may be linked to dietary changes resulting from anthropogenic influences and highlights the species’ resilience in adapting to these changes.

Adapting to a new world

In previous studies conducted by Dhawale and her team, the species’ adaptability to a rapidly changing landscape was clearly evident. In one of these studies, Dhawale and her team explored the concept of “synurbanisation” in lion-tailed macaques, where urbanisation processes impact the species’ behaviours and ecological dependencies.

This refers to the phenomenon where the macaque population either starts utilising certain changes or infrastructures that come about as part of urbanisation, or begins altering their behaviour in response to these changes in their habitat – or both.

“For example, roads are a key part of the urbanisation process,” says Dhawale. “The synurbanisation process for lion-tailed macaques occurs when they start using roads that cut through the forest, realising that these roads not only help them move across fragmented forest patches but also provide opportunities to interact with humans and their artifacts, such as food handouts.”

The road that cuts through the Puthuthottam forest patch has become an integral part of the macaques’ habitat, as they need to constantly use it to access their natural range. Synurbanisation manifested in the form of the macaques spending more time in and around the road. “Initially, they would only use it to cross, but over time, they started to linger, spending more time on or near the road,” highlights Dhawale.

When the research team examined whether the macaques were actively choosing to use the road or avoiding it, given that it had become part of their home range, they found that most of them preferred it and used it actively.

“Looking at their diet, we found that macaques began incorporating human-provided foods, or ‘human-use foods’, into their diet. These include food scraps left by humans, garbage along the road, or food discarded in dumpsters. In some groups, human food makes up a significant portion of their diet – one group, for instance, relies on human foods for about 80% of their intake,” Dhawale says.

The forest patches have poor canopy connectivity, which is not ideal for a species that is fully arboreal. The patches are also surrounded by tea plantations, which the macaques avoid due to the risk of predators, such as leopards, that can hide in the dense undergrowth. Given this scenario, the road became a key factor when an entire group of macaques used it to completely leave the forest fragment.

“This migration, which we discuss in the paper, led the group to a nearby human settlement where they had easy access to food. They also found an acacia tree. While the acacia is not native to the area, it provided the macaques with some form of arboreal habitat,” Dhawale explains.

Principal scientist at the Salim Ali Centre for Ornithology and Natural History, Honnavalli N. Kumara, who has studied the species since the early 2000s, says that the macaques began showing signs of adaptability to anthropogenic pressures as early as the late 90s, when their habitat started changing.

A paper co-authored by Kumara in 2001 highlights this trend, noting that the loss of canopy contiguity and changes in vegetation in the rainforest were key factors forcing the almost wholly arboreal lion-tailed macaques to spend more time on the ground in this area. The paper also points to significant shifts in the species’ diet, ranging patterns, and other behaviours.

“In 1995, there was only one group of lion-tailed macaques, with about 33 individuals. By 2000-2002, the group had split into two. Three years later, there were about three groups, and by 2015, there were four groups with over 120 individuals,” he recounts. “The pressure for space became overwhelming, and they began moving into towns and other human settlements. Their natural diet was significantly impacted,” he adds.

Due to the reduced habitat and increased numbers, the macaque groups frequently encounter one another, leading to constant pressure to move, avoid each other, and adapt to the limited space.

You are what you eat

While the adaptability has allowed the population of lion-tailed macaques to grow, it also poses significant risks. Dhawale highlights accidents and injuries to extremities, such as limbs and tails, which result from crossing roads or foraging in dumpsters and open spaces. “These injuries occur because the macaques are interacting with human-built objects, like dumpsters with metal edges, house windows, roofs, and so on,” she explains.

It also makes them more vulnerable to human hostility. “The forest department is under pressure to translocate some populations but we can’t come up with management strategies without understanding the details of conflict fully,” Kumara says. The more they take refuge in human habitation, the more the chance of hostility from humans, he adds.

Feeding constantly on human-use foods can also affect their overall health, although it can’t be proven in the absence of physiological analyses, says Dhawale. Human food is generally higher in carbohydrates, fats, and complex sugars, leading to a quicker sense of satiety compared to the macaques’ natural diet which include mainly fruits and nuts, but also insects, lizards, etc.

“While the macaques may feel full more quickly, their evolutionary behaviour doesn’t change. They continue to spend a large portion of their time foraging, as continuous foraging is hardwired into them – about 80% of their time is dedicated to foraging,” she explains.

A 2013 study examined the prevalence of parasites in the guts of 91 lion-tailed macaques across nine forest fragments in the region. The study identified nine gastrointestinal parasite taxa, with 75.8% of the samples showing at least one parasite. It found that smaller forest fragments, especially those near human activities, had higher parasite diversity and prevalence. This suggests that habitat fragmentation exacerbates parasitic infections, the paper notes.

Authorities must urgently address corridor connectivity and restore forest patches to ensure the long-term survival of this endangered species, says Kumara. Another 2013 study on the potential solutions suggest that to connect three isolated populations of lion-tailed macaques in Valparai, a minimum area of 1.56 square kilometres is needed, encompassing various land-use types such as seasonal stream beds and cultivated areas.

“In Karnataka, too, the populations of lion-tailed macaques are splitting and expanding. The government has designated about 1,000 square kilometres in Sharavathi, Shimoga, as a lion-tailed macaque sanctuary, providing ample space for the species to grow and expand. Valparai should consider a similar solution,” Kumara concludes.

This article was first published on Mongabay.