Camera traps reveal hidden treasures of the rainforest

In their new research, Mattia Bessone and colleagues demonstrate how camera trap distance sampling can be used to develop conservation strategies and protect threatened species.

The impact humans are exerting on the planet is accelerating the loss of biodiversity, with animal species disappearing at such unprecedented rate that scientists have labelled the current era ‘Earth’s sixth mass extinction’. To preserve the remnants of wildlife we need methods effective in monitoring animal population status, thus allowing the development of conservation strategies. This is particularly urgent in tropical rainforests; habitats that harbour stunning biodiversity but where ecological information is scarce for the majority of the endemic vertebrates. In Africa’s Congo basin, one of the most diverse areas of our planet, we are witnessing dramatic population declines and local extinctions of charismatic animals such as elephants and great apes. Yet, we still know very little about other species inhabiting these remote forests.

Installing camera traps in Salonga National Park. Photo: ©Jonas Abana Eriksson

In our research, we estimated vertebrate density in the block South of Salonga National Park, Democratic Republic of the Congo, Africa’s largest protected area of pristine rainforest, using a recently described monitoring method: Camera Trap Distance Sampling (CTDS) . CTDS estimates animal abundance by adjusting point transect distance sampling methods to the use of camera traps (CTs). Allowing the detection of cryptic and nocturnal species, mostly overlooked by monitoring methods where human observers are involved, CTs are extremely useful tools in the thick vegetation of tropical rainforests.

The video above shows some of the impressive camera trap footage captured by the team 

Taking advantage of a consolidated mathematical framework, open-source software and a vast community of users and developers, CTDS is easily accessible to both fundamental and applied research. Its accuracy has been validated under controlled field conditions and it can be considered among the most promising methods to assess animal density and abundance in forest habitats to date.

We applied CTDS to a diverse vertebrate community and obtained density estimates of 14 under-known species differing in physical, behavioural and ecological traits. Among these, we obtained the first estimates ever published for the Congo peafowl, the giant ground pangolin (both at risk of extinction) and the cusimanses, an unchartered genus of small, social, mongooses. In addition, we obtained density values of endemic and endangered species such as the Allen’s swamp monkey, the bonobo, the forest elephant and the African golden cat.

Highlighting practical pitfalls, such as animal reactivity to the camera, our study provides methodological recommendations for future surveys and shows the wide applicability of CTDS as a method allowing a simultaneous survey of a large proportion of the terrestrial vertebrate community, rather than single species surveys. The results obtained by the application of CTDS will translate into the revision of species’ conservation status in the IUCN Red List of Threatened Species, providing the basis for continuous monitoring and population trend evaluation, crucial for the implementation of effective conservation plans.

Read the full article, Drawn out of the shadows: Surveying secretive forest species with camera trap distance sampling, in Journal of Applied Ecology.

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