One orangutan, two orangutans, three orangutans, four

SFU PhD candidate in the faculty of Resource and Environmental Management Brent Loken has co-authored a study which describes a new method for estimating orangutan density using camera traps.

According to census data gathered in 2003, there are about 45,000 to 65,000 of these apes remaining and are all found in either Borneo or Sumatra. The large margin between those figures is attributed to how difficult it is to count orangutans that are on the move, often monkeying around in the treetops.

To study the density of animal populations, researchers previously have relied on methods that convert nest counts to species densities. These methods require a substantial effort for reliable results, and researchers are especially challenged to study species which are endangered or in low densities.

Loken explained that obtaining more definite numbers will help with conservation efforts:

“It’s extremely difficult to protect an endangered species if we don’t know how many are there.”

Over the period of the study, which lasted for six months, 70 cameras captured a sample of 7,320 trap days, which resulted in a total of 658 photographs.

There were some repeats of the individuals or groups of orangutans due to the fact that three photos were captured per trigger. The photos were analyzed to determine whether the orangutans captured were the same individual apes they had seen before or different ones based on a number of different indicators such as body size, facial features, and secondary sexual characteristics.   

In addition to nest count surveys, data was collected using camera trapping and spatial capture-recapture (SCR) models, which, although imprecise, allow for a better estimate of orangutan encounters.

The results suggest that with methodological adjustments, camera trapping and SCR modelling could be successfully used to estimate the densities of orangutans and, potentially, other elusive primates.

Loken says that this is the first time this method has been used for orangutans and it has the potential to greatly improve our knowledge about the number of orangutans left in the wild.

“This is a big step forward in helping to better understand how many orangutans remain in the wild and where they live,” he said.