838 R. Costa‐Araújo et al.


Plecturocebus vieirai (Plate 1). This species was recently dis- covered in the Arc of Deforestation (Gualda-Barros et al., 2012) but is known only from its pelage colour and occur- rence in three localities and is therefore considered Data Deficient (Alonso et al., 2018; IUCN, 2021). Using our find- ings, we discuss the threats to primates and the opportun- ities for biodiversity conservation coupled with climate change mitigation and income generation in the Arc of Deforestation using P. vieirai as an emblematic example, a species that we assess to be Critically Endangered based on the IUCN Red List criteria (IUCN, 2019).


Study area PLATE 1 Vieira’s titi monkey Plecturocebus vieirai. Photo: F. Reis.


expansion of agriculture and settlements have transformed southern Amazonia, adjacent ecotonal forests and the north- ern Cerrado into the largest global deforestation frontier (Kirby et al., 2006;FAO, 2016; Silva et al., 2019; Montibeller et al., 2020), known as the Arc of Deforestation, significantly affecting the functioning of the Amazonian ecosystem (Nobre et al., 2016;Gatti et al., 2021). There are 52 primate species in the Arc of Deforestation.


The majority are endemic to this region and approximately half are threatened or near threatened with extinction (Costa-Araújo et al., 2021b). At the same time, there is a scarcity of baseline data on these primates, including a sig- nificant taxonomic deficit (Costa-Araújo et al., 2019; Byrne et al., 2021), which hampers the protection of these species (Rylands&Mittermeier, 2014). An understanding of species diversity, distribution and abundance is therefore necessary to clarify and quantify extinction risks and to provide a sci- entific foundation for the conservation of the poorly studied primates endemic to the Arc of Deforestation. Investment in research into and the conservation of pri-


mates is especially important as they play a vital role in eco- system functioning (Peres et al., 2016; Trolliet et al., 2016; Heymann et al., 2017), and they are the most vulnerable ver- tebrate group globally (Arroyo-Rodríguez et al., 2013, 2017), with c. 60%of all primate species threatened to some degree (Estrada et al., 2017). Moreover, primates are valuable as flagship species (Dietz et al., 1994; Chapman et al., 2020), and so the protection of their habitats in the Arc of Deforestation will not only contribute to their conservation but also provide protection to other species endemic to this region, contributing to biodiversity conservation with impacts at local, regional and global scales. Here we identify the areas of suitable habitat, delimit


the geographical distribution, estimate the population size and assess the conservation status of Vieira’s titi monkey


The study area is located in the Tapajós–Xingu interfluve, a region within the Arc of Deforestation that is especially susceptible to land-use change (Laurance et al., 2002; Fig. 1). The Arc of Deforestation extends across southern Amazonia, ecotonal forests and the northern Cerrado from its eastern edge in the states of Pará and Maranhão to the state of Acre in the west (Fearnside et al., 2009; Silva et al., 2019). This region accounts for almost half of the total global land-use changes during 1990–2015 (FAO, 2016). Although sustainable development was expected for the Tapajós–Xingu region 2 decades ago (Nepstad et al., 2002), it became an epicentre of deforestation as a result of logging and slash-and-burn clearance for agriculture and cattle ranching as well as legal and illegal gold mining, affecting even protected areas and Indigenous lands (Printes, 2017; Montibeller et al., 2020).


Methods Data collection


We collected new occurrence records in field expeditions within the Tapajós–Xingu interfluve during 2015–2019 to model areas of suitable habitat and to delimit the geographical distribution of P. vieirai. We reviewed the literature and examined specimens housed in museum collections in Brazil, the USA and Europe for additional occurrence records. To estimate the size and density of the P. vieirai population, we surveyed four areas during 2016–2018 using the linear transect method (Buckland et al., 1993). In each area we established a transect of 5 km covering mature and secondary forests. Each tran- sect was surveyed at a constant speed of c. 1.25 km/h twice daily, at 07.00–11.00 and 14.00–18.00 by DAS, LFS and RMA. We noted the number of individuals and the perpendicular distance between the group and the transect using a GPS and ameasuring tape; we considered each of the two daily surveys to be independent (Peres & Cunha, 2011). The four forest areas surveyed are on the east bank of the middle Teles Pires River in the


Oryx, 2022, 56(6), 837–845 © The Author(s), 2022. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S003060532100171X


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