Researchers in the 3,6 million hectare Salonga National Park (Africa’s largest tropical rainforest reserve) in the Democratic Republic of the Congo set up 160 camera traps in 743 locations and used a new method of analysis known as “camera trap distance sampling” to estimate animal abundance in this, one of Africa’s richest biodiversity habitats.
Camera traps have revolutionised wildlife research in allowing data to be collected on specie’s distribution, density, abundance, behaviour and social structure without the presence of a human observer. They have proved to be an indispensable tool, particularly in challenging environments such as dense rainforests or in dealing with shy, elusive or even dangerous animal species. Their value has been clear for many years but only recently have scientists found ways to use them to evaluate actual population data accurately. These population and density estimates are, in turn, crucial in evaluating the conservation status of individual animal species and ensuring that the correct measures can be implemented for their protection.
In a study published in the Journal of Applied Ecology, biologists describe how they covered 17,127km2 (1,712,700 hectares) from September 2016 to May 2018, systematically placing camera traps between 70 to 90cm above the ground. These produced more than 16,000 video clips with over 170 hours of animal footage that revealed the secretive species.
In the past, camera trap footage and images could only be used to estimate populations of animals with distinctive markings such as leopards, where individuals could be identified and recognised in future images. For animals with more obscure or indistinct individual markers, it was far more challenging to avoid counting the same individual twice at different locations. This study focused on using camera trap distance sampling – subdividing the time the cameras were active into “snapshots” where at a specific and predetermined moment, one individual animal could only be in one location at one point in time.
The results of this method allowed this study to provide the first-ever estimates of the population sizes of species such as the Congo peafowl and giant ground pangolin. For the peafowl, the results of the study were positive – the numbers seem to be far higher than previously thought. For the giant ground pangolin, the researchers concluded that the population estimates are far more concerning, with fewer than 1,000 individuals in an enormous and, presumably vital, portion of their natural distribution.
Most importantly, the methods utilised by the researchers show that camera trap distance sampling is an essential survey method to provide valuable information on wildlife density and abundance. Previously, conservation efforts aimed at the protection of elusive species like the African golden cat or four-toed sengi (a type of elephant-shrew) were mainly based on educated guesses as to their numbers, but this study has provided a concrete way of estimating their actual wild abundance. According to the authors, this in turn “gives an insight into the complex and delicate equilibrium of the rainforest community and the threats to its survival.”
