Titi monkeys are small, shy, fruit-eating primates. They represent the most diverse Neotropical primate radiation and are widely distributed across South America. They can be found in a broad range of forest habitats, including primary and secondary, flooded and unflooded, tropical moist deciduous and dry forests. Like all Neotropical primates, titi monkeys are highly dependent on tropical forests. Information is still lacking on how deforestation affects titi monkey populations. It is therefore essential to assess their conservation status and design strategies for their conservation.

Conservation status is assessed based on the data and expert knowledge available on the potential threats to and the characteristics of the species. When a species does not meet any criteria of a threatened category, it is categorized as Least Concern on the IUCN Red List. However, in many cases, the lack of information hampers the assessment of a species’ conservation status, and the absence of evidence may not be evidence of absence.

Plecturocebus bernhardi. Photos: Marcelo Santana

Prince Bernhard’s titi monkey Plecturocebus bernhardi is one such case. Information on its occurrence and distribution is limited to a few studies, and the assessment of its conservation status did not include data on population size and threats. The relatively large range of P. bernhardi was the main justification to categorize it as Least Concern. The species occurs in the southern Brazilian Amazon Rainforest, on the border between Amazonas, Mato Grosso, and Rondônia states. This region has one of the highest deforestation rates in the Brazilian Amazon and is known as the Arc of Deforestation. Our team of researchers from several universities, together with colleagues from governmental and non-governmental organizations, carried out a series of surveys. Our aim was to gather evidence to investigate whether the titi monkey was more threatened than previously thought.

Along with population surveys, we used spatial predictive modelling to estimate the amount of habitat loss for the species. We looked at predictions for the next 24 years, which corresponds to three titi monkey generations. We assessed habitat loss under two scenarios: governance, and business-as-usual. Although P. bernhardi occurs over an area of 131,295 km2, we estimated a habitat loss of 58,365 km2 (44.5% of the species range) under the governance scenario and 105,289 km2 (80.2%) under the business-as-usual scenario. This amount of habitat loss indicates that the species meets the IUCN Red List criteria for Vulnerable, at least. We recommend P. bernhardi categorized as such in both the national and global red lists.

Left: Amazon Rainforest on fire. Right: Surveying primates in the Amazon Rainforest. Photos: Marcelo Santana

These findings potentially shed light on the status of the other 17 titi monkey species that live in the Amazon rainforest and are currently also categorized as Least Concern based on the same arguments used for P. bernhardi. These include their large range, presence in protected areas, or absence of evidence of threats to their populations. However, although P. bernhardi has a large range, its habitat is highly fragmented in the southern portion of its distribution. Although protected areas and Indigenous lands are essential to counter deforestation in the Brazilian Amazon, several initiatives promoted by the current government, and by some politicians associated with agribusiness, are undermining the conservation effectiveness of these areas and encouraging violations of environmental regulations.

Left: The Aripuanã River. Right: Selective logging. Photos: Marcelo Santana

These initiatives come as proposed bills such as PL 191/2020 and PL 490/2007, which would allow mining and hydropower dams within Indigenous lands, and the so-called land-grabbing bills PL2633/2020 and PL510/2021, which grant an amnesty to land-grabbers and invaders that irregularly occupy exploited and deforested federal lands. This backdrop of impunity promotes activities such as land grabbing, illegal logging, mining and fire that increase deforestation in the southern Amazon . Together, these actions are disastrous not only for species conservation but for the protection of the social well-being of the traditional peoples of this region.

The conservation status of primates inhabiting the Arc of Deforestation needs to be evaluated by considering both their current status and potential future scenarios. If the absence of evidence of threats is because of lack of information, then a species should be considered Data Deficient, which indicates it requires more data to evaluate its conservation status. We hope that similar approaches are considered in the assessment of the conservation status of other Amazonian species. As a practical implication of our findings, we hope that P. bernhardi is included in the National Action Plan of Amazonian primates and that its conservation status is updated in both the national and global Red Lists of threatened species.

Taking the motorboat, “rabeta”, in the Aripuanã River into the deep rainforest. Time-lapse video: Marcelo Santana

The article Using population surveys and models to reassess the conservation status of an endemic Amazonian titi monkey in a deforestation hotspot is available in Oryx—The International Journal of Conservation.

Felipe Ennes Silva is a primatologist interested in the ecology, evolution, and conservation of Neotropical primates. Currently, he is a postdoctoral researcher under the Marie-Curie fellowship scheme at the Université Libre de Brussels where he investigates the genetic diversity of Amazonian primates using whole-genome sequencing. Felipe is a research collaborator at the Mamirauá Institute for Sustainable Development. He is also collaborating with the Primate Genome Project and in 2022 became a member of the IUCN Species Survival Commission Primate Specialist Group.