A new method for modeling free-ranging animal populations has found smaller-than-expected macaque numbers

A team of researchers developed a new modeling method to estimate the population of free-ranging animals and in doing so found that the Old World monkey, the macaque, was far less numerous than expected.

Ph.D. candidate at the University of Western Australia’s School of Human Sciences, Xueying Zhu was a co-author of the published paper. Scientific advances.

Accurately estimating population size for free-living animals using non-invasive methods such as camera trap images is limited by individual identification, the small number of areas and the size of the datasets, Zhu said.

„Tracking animal movement using tag-and-retrieve methods or GPS tagging provides a solution, but inevitably disrupts the movement and behavior of animals and requires a lot of scientific resources and trained labor,” Zhu said.

„We developed a flexible model and used it to estimate the upper limit of the population of the long-tailed macaque; a wild animal often considered a pest.”

The long-tailed macaque, Macaca fascicularis, is a species native to Southeast Asian countries such as the Philippines, Malaysia, Indonesia, Burma, India, Vietnam, Cambodia, Laos, and Thailand, and has a long history with humans.

The researchers created habitat preference maps based on environmental and GPS data, using probability of distribution sampling, and creating an estimate with data from camera traps, line transect distance sampling, and direct sightings.

The study found that long-tailed macaque populations may be up to 80% smaller than previously thought.

„We recommend prioritizing and improving conservation measures for this species and continuing to monitor and study trends in its population dynamics,” Zhu said.

„Additionally, we believe in the use of citizen science data and encourage its integration into greater wildlife conservation to increase data availability.”

The modeling developed by the researchers is flexible, making it suitable for studying multiple species, providing a scalable, non-invasive tool for wildlife conservation.