# Sleeping-Site Decisions in Tibetan Macaques: Social and Seasonal Drivers

## TL;DR

Tibetan macaques change where they sleep based on the season, with females playing a key role in making these group decisions.

## Contribution

This study reveals how social and seasonal factors influence collective sleeping-site decisions in Tibetan macaques.

## Key findings

- Tibetan macaques switch between arboreal and terrestrial sleeping sites depending on the season.
- Females are central to initiating and influencing collective sleeping-site decisions across seasons.
- Older individuals and socially central individuals play key roles in movement decisions during the mating season.

## Abstract

How do Tibetan macaques exhibit seasonal variations in sleeping-site selection and what are the underlying collective decision-making processes? In this study, we not only investigated the arboreal and terrestrial sleeping-site selection of free-ranging Tibetan macaques in Huangshan across mating and non-mating seasons, but also identified the key factors influencing these collective decisions. We found that these macaques switch their sleeping sites between the two seasons. Females played a central role throughout the study, initiating more arboreal movements in the mating season and joining movements earlier across all periods. Furthermore, older individuals and females dominated most terrestrial movements in the mating season; in the non-mating season, no specific social factors could predict movement initiators, yet females retained their advantage in attracting followers. These findings provide valuable insights into how social animals adjust collective decision-making to adapt to seasonal environments.

Sleeping-site selection is a critical decision-making process in animals, influenced by evolutionary pressures. However, the key factors controlling this choice under group demography, and how these vary seasonally, remain poorly understood. This study investigated the selection of arboreal versus terrestrial sleeping sites and the underlying decision-making processes in a free-ranging group of Tibetan macaques (Macaca thibetana) at Huangshan, China, across mating (July–January) and non-mating (February–April) seasons. Generally, Tibetan macaques slept arboreally during mating season (July–September), switched to terrestrial sites afterward (October–March), and returned to trees in the following April. As for the decision-making, females consistently played a central role, initiating collective movements to arboreal sites more frequently and attracting more followers during the mating season, and joining the collective movements earlier across all seasons. Decision-making rules also varied seasonally. Females and middle-aged/older individuals mainly initiated movements to arboreal sites during the mating season, whereas terrestrial movements were led primarily by older individuals, with high social centrality attracting more followers. In the non-mating season, no specific social traits predicted initiators across sleeping sites, though females consistently attracted more followers and joined movements earlier. In terrestrial movements specifically, older individuals joined later, whereas highly socially central individuals joined earlier. Our research reveals that the sleeping-site selection decisions of Tibetan macaques are influenced by their matrilineal group structure. This study provides insights into the ecological adaptability of primates, demonstrating how dynamic decision-making supports survival in seasonal environments among social animals.