Japanese macaques population growth

Introduction to the Study

The relocation of 38 Japanese macaques from Japan to Austria in 1996 created a unique opportunity to follow a primate population from its first days in a new environment. The animals were moved from the Minoo-H group in Osaka Prefecture to Affenberg Landskron, a forested enclosure in southern Austria.

Over the following 23 years, the group grew steadily, reaching 160 individuals by January 2020. A study published in the journal Primates examined the population’s births, deaths, reproduction and social structure, revealing how the group developed over more than two decades.

Background and History

The Japanese macaques, also known as Macaca fuscata, are native to Japan and are known for their distinctive physical and behavioral characteristics. The species is listed as vulnerable on the IUCN Red List, due to habitat loss and fragmentation, as well as other human activities.

The introduction of the Japanese macaques to Austria was a significant event, as it allowed researchers to study the population in a controlled environment and gain insights into their behavior, social structure, and population dynamics.

Population Growth and Development

The 38 macaques arrived in August 1996 after being moved from Japan. The founding group consisted of 13 sexually mature females, 10 younger females and 15 immature males. No adult males were among the animals brought to Austria.

After 12 days of quarantine and medical checks, they were released into a 4-hectare enclosure of natural forest at Affenberg Landskron. The site included spruce trees, shrubs, grassland, swampy areas and a small stream, giving the macaques space to move and forage.

The population experienced a small decline during its first year, but recovered quickly. One year after arrival, it recorded its highest annual growth rate of 25%. By 1 January 2020, the group had reached 160 individuals.

Food and Management

Food availability was an important part of life at Affenberg. The macaques could eat natural vegetation, including leaves, seeds, bark, roots, flower buds and insects, but this was not considered sufficient throughout the year.

The group received additional food, with supplies adjusted according to its size and the seasonal conditions. By January 2020, when there were 160 macaques, the daily provisions included around 8–10 kilograms of wheat, 80 kilograms of apples, 20 kilograms of carrots and 60 kilograms of potatoes.

Reproduction and Births

The study recorded 223 births between 1997 and 2019, including 104 females, 116 males and 3 whose sex could not be determined. Most females that reproduced for the first time did so between four and five years of age, with the average age at first birth being 4.92 years.

Births were not evenly spread throughout the year. Apart from two unusual births, the birth season ran from mid-March to late July, with the largest numbers occurring in late April and late May.

Time Between Births

The time between births varied considerably. Across the population, the average interval was 1.68 years, although individual intervals ranged from 0.88 to 4.31 years.

One notable pattern appeared after the loss of an infant. Females gave birth again after an average of 1.10 years when their previous infant had died, compared with 1.77 years when the infant survived.

Population Change and Social Structure

The population gradually changed from a group dominated by younger animals into one containing a substantial number of older macaques. When the founders arrived, 60.5% were younger than 4 years, while none was older than 18.

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By January 2020, 22.5% were younger than four and 17.5 percent were older than 18. The oldest living animals at that point were a 32-year-old female and a 23-year-old male.

Deaths and Mortality

Deaths were also recorded throughout the study. There were 102 deaths, including 43 females, 56 males and 3 individuals whose sex was unknown.

Confirmed causes included severe wounds, infections, blunt trauma and cancer, although the cause was not always possible to establish. Infant mortality was relatively low, with 20 of 223 live-born infants dying before reaching one year, giving a rate of 8.97%.

Implications for Conservation and Management

The study of the Japanese macaque population in Austria has important implications for conservation and management of primate populations. The findings highlight the importance of considering the social structure, behavior, and population dynamics of the species when developing conservation strategies.

The study also demonstrates the value of long-term monitoring and research, which can provide valuable insights into the dynamics of primate populations and inform effective conservation and management practices.

Expert Perspective

According to experts, the study of the Japanese macaque population in Austria is a significant contribution to the field of primatology and conservation biology. The findings of the study have important implications for the management and conservation of primate populations, and highlight the need for continued research and monitoring.

Conclusion

The study of the Japanese macaque population in Austria provides valuable insights into the growth and development of a primate population in a new environment.

The population’s growth, reproduction, and social structure were all influenced by various factors, including food availability, management, and individual characteristics.

• The population grew from 38 to 160 individuals over 23 years.
• The average age at first birth was 4.92 years.
• The time between births varied considerably, with an average interval of 1.68 years.
• The population developed a stable social structure, with 11 intact maternal lines and changes in the positions of high-ranking males over the years.

What to Watch Next

Future research should continue to monitor the population and study its dynamics, behavior, and social structure. Additionally, the study of the Japanese macaque population in Austria can inform conservation and management practices for other primate species.

The implications of the study for conservation and management of primate populations are significant, and highlight the need for continued research and monitoring to inform effective conservation practices.