As roads and railways threaten primates, Brazil is a global hotspot

As roads and railways threaten primates, Brazil is a global hotspot

  • A study mapping out the regions of the world where primates face the greatest risk from infrastructure such as roads, railways, power lines and pipelines has identified Brazil, Thailand, Indonesia and China atop the list.
  • Of the 512 known primate species, 92, or 18%, are directly affected by roads and railways; threats come from vehicle impacts as well as the “barrier effect” that the infrastructure poses, limiting the mobility of tree-dwelling animals.
  • Some 25 million kilometers (15 million miles) of roads and railways are expected to be built by 2050, of which 90% will be in less-industrialized countries, including tropical regions that are home to rich primate diversity.
  • Nearly 200 million hectares (almost 500 million acres) of tropical forest have been lost over the past 20 years in regions where primates live, with Brazil’s Atlantic Forest and the Amazon considered high-priority areas for mitigation and preservation measures.

Brazil should be the country of highest priority for measures to save primates from the threats posed by roads and railway lines, according to a study. It highlighted the Amazon and the Atlantic Forest as the regions most in need of preservation and mitigation actions, and recommended that the construction of roads, railways, power lines, pipelines and waterways be avoided because of the vulnerability of native primate species.

The study, published March 2021 in the International Journal of Primatology, was carried out by researchers in Portugal and Spain. It found that 65% of the planet’s primates are at risk of extinction, with the greatest visible threats coming from the expansion of agribusiness, illegal logging, hunting, and capture.

“Transportation infrastructure like highways and railways, power lines, pipelines and artificial waterways also have a hand in the current biodiversity crisis, but are oftentimes forgotten,” the study’s authors say.

Of the 512 known primate species, 92, or 18%, are directly impacted by road and rail infrastructure, the study says, citing data from the IUCN, the global wildlife conservation authority.

Aside from the more obvious threat from vehicle impacts, roads and railways also pose what’s known as a “barrier effect,” inhibiting or impeding the mobility of wildlife through their habitat. This is especially the case for species that move through the treetops. The presence of transportation infrastructure has also been shown to lead to increased deforestation and human occupation of previously inaccessible areas, with all the attendant threats: the spread of disease, hunting, wildlife trafficking, and more.

And without measures to address the problem, the situation could get worse, the study says. It notes that 25 million kilometers (15 million miles) of new roads and railways are slated for construction worldwide by 2050, 90% of them in less-industrialized countries, including tropical regions with rich primate diversity.

A Guyanan red howler (Alouatta macconnelli) killed on the BR-174 highway near the border between the Brazilian states of Roraima and Amazonas. Image courtesy of Fernanda Abra.

Mitigation and preservation

The study ranked primate-rich regions around the world into two categories: one with a high density of transportation infrastructure, where mitigation measures should be prioritized, and the other with low density, where preservation against new infrastructure is preferable. The Atlantic Forest topped the ranking for “primate mitigation areas,” while the Amazon led the one for “primate preservation areas.”

Study lead author Fernando Ascensão, a biologist at the University of Lisbon’s School of Sciences, told Mongabay that “the idea of having these two rankings is to make it possible to manage the infrastructure networks in a differentiated manner.”

“There are zones on the planet, or different regions within countries — it doesn’t matter which scale we consider — in which we need to mitigate. [This is] where infrastructure has already been built and is impacting biodiversity, especially primates,” Ascensão said. “And there are zones where there is still no significant influence from infrastructure, particularly the tropics. These zones should be maintained as much as possible. Given the negative impacts, construction of infrastructure should be avoided there.”

To create the rankings, the researchers used IUCN data on 475 primate species distributed in four regions: the Neotropics (Central and South America), Africa, Madagascar (geopolitically part of Africa, but with a primate richness that warrants its own distinction), and Asia.

The researchers obtained localization and distribution of roads, railways and other structures in these regions from the OpenStreetMap platform, a collaborative mapping project. They also reviewed published studies on the issue and conducted a poll via questionnaire of primatologists around the globe.

With all this data, the researchers created two maps. One shows the countries according to their conservation ratings, indicating priority areas that should be protected as they are still home to rich primate diversity, and the other with countries according to the density of infrastructure already installed. Transposing these two maps enabled them researchers to identify the primate mitigation areas and the primate preservation areas.

Map A shows the regions with the richest primate diversity, while Map B shows infrastructure density (roads, railways, power lines, pipelines and man-made canals). Map C transposes the two, allowing researchers to identify the priority regions for evaluation of global risk for primate survival. Image courtesy of Ascensão et al. (2021).

Priority regions

The countries that ranked highest for conservation due to the richness of primates and heavy impact of existing roadways and railways were Brazil, Thailand, Indonesia and China, in that order. The Atlantic Forest, which in Brazil has been reduced to just 10% of its original expanse, was pinpointed by Ascensão as an area where “infrastructure mitigation is urgently needed.”

The study also identified the 12 primate species most vulnerable to the impacts of high infrastructure density in the Neotropics, which include Brazil.

“These are species to which priority should be given in infrastructure management, especially the establishment of bridges and corridors between patches of habitat,” Ascensão said. Such has been the case of the golden lion tamarin, which is the focus of important mitigation measures taken on the BR-101 highway. These projects were the fruit of the work of many researchers, especially the folks at the Golden Lion Tamarin Association.”

Mongabay reported in October 2020 on the construction of forested bridges to help wildlife cross a freeway in Brazil. The infrastructure was built to connect the sections of Atlantic Rainforest still standing along BR-101 in the municipality of Silva Jardim in Rio de Janeiro state.

In addition to this bridge, the company holding the concession for BR-101, Arteris Fluminense, was required to install 15 wildlife tunnels under the highway, 10 structures connecting treetops on opposite sides of the road —specifically for arboreal fauna such as the golden lion tamarin (Leontopithecus rosalia) — nine bridges, more than 30 km (19 mi) of fencing, and signs alerting drivers to the presence of wildlife. All this was installed along a 72-km (45-mi) stretch of the highway running between the municipalities of Rio Bonito, Silva Jardim and Casimiro de Abreu in Rio de Janeiro state.

These wildlife passages are meant to mitigate the barrier effect created by the road and allow the wildlife to resume moving between isolated patches of forest.

A wildlife crossing bridge over the BR-101 highway in the municipality of Silva Jardim, Rio de Janeiro state. Image courtesy of the Golden Lion Tamarin Association.

Fabiano Rodrigues de Melo, a professor of primatology at the Federal University of Viçosa in Minas Gerai state, told Mongabay that the loss of landscape connectivity due to the highway has isolated groups of animals of the same species. This restricts the exchange of genetic material among the animals, compromising their ability to adapt to change in the environments in which they live.

Aside from the golden lion tamarin, the list of species most vulnerable in regions with high road and railway density in the Neotropics include the blond capuchin (Sapajus flavius), the black lion tamarin (Leontopithecus chrysopygus), the golden-headed lion tamarin (Leontopithecus chrysomelas), the brown howler monkey (Alouatta guariba), the Maranhão red-handed howler monkey, (Alouatta ululata), the common marmoset (Callithrix jacchus), the black-tufted marmoset (Callithrix penicillata), Wied’s marmoset (Callithrix kuhlii), the buffy-headed marmoset (Callithrix flaviceps), the buffy tufted-ear marmoset (Callithrix aurita) and the Geoffroy’s tufted-ear marmoset (Callithrix geoffroyi). All are found in Brazil.

Another 20 species from other regions around the globe were also considered highly vulnerable to the existing roads and railways in their habitats.

A buffy tufted-ear marmoset (Callithrix aurita). Image courtesy of Rodrigo Salles de Carvalho/CPB-ICMBio.

Brazil also headed the list of regions with rich primate diversity but few roads and railways. The Amazon River Basin stood out in this ranking, followed by the Democratic Republic of Congo, Colombia and Indonesia.

“The species in these regions should be targeted by different programs offering measures to keep the habitat from being fragmented,” Ascensão said. “Building roadways should be avoided.”

He said monkeys like the Juruá red howler monkey (Alouatta juara), the Guyanan red howler (Alouatta macconnelli) and the black howler (Alouatta nigerrima), whose conservation status is less dire, will probably be heavily impacted if human activity reaches their territories.

Looking for solutions in the Brazilian Amazon

Fernanda Abra, a post-doctoral biology researcher at the Smithsonian Institution’s Center for Conservation and Sustainability (CCS) in the U.S., is developing a project called Reconecta to test two models of bridges for arboreal wildlife over the BR-174 highway, which connects the city of Manaus in the state of Amazonas state with Boa Vista in Roraima state, crossing the Waimiri-Atroari Indigenous Territory.

“The Reconecta project aims to gain scientifically based information to orient the [implementation] of adequate wildlife bridges with a good cost-benefit to help primates and other species that travel in treetops,” said Abra, who was not involved in the 2021 study.

Thirty structures are being built along 125 km (78 mi) of paved highway cutting through a well-preserved section of the Amazon Rainforest. Their locations were chosen after consultations with leaders of the Indigenous community, who know the region’s wildlife well.

Half of the bridges will have simple structures of very thick rope, and the rest will be built from woven ropes. Abra said it’s challenging to conceive of structure models for primates, given that the species that will use them will have different modes of mobility, from jumping to walking on four legs to swinging from branch to branch.

Two golden-handed tamarins (Saguinus midas) killed on the BR-174 highway near the border between the Brazilian states of Roraima and Amazonas. Image courtesy of Fernanda Abra.

More than 15 arboreal species live in the stretch of forest where the study is being performed. They include hedgehogs, marsupials, rodents, reptiles and primates such as the Guiana spider monkey (Ateles paniscus), a threatened species known for its reluctance to cross roads.

In splitting an area of forest, a road doesn’t just introduce the movement of people and vehicles, but also acts as a barrier preventing arboreal wildlife from crossing, Abra said. “Those killed on the roadway are the semi-arboreal animals. For the ones who live exclusively in trees, the problem is the barrier effect, an invisible consequence that, in the long term, is extremely dangerous for this fauna,” she told Mongabay.

The Reconecta project, which began with monitoring roadkill numbers in September 2021, will last for two and a half years. The posts that will support the bridges are currently being installed. As soon as the wildlife bridges are ready, camera monitoring will begin to verify which animals are using the new structures, how they behave, and how effective each model is.

Abra said the results of the study will be sent to the National Department of Transportation Infrastructure (DNIT). Seminars will be prepared together with that department and the National Center for Brazilian Primate Research and Conservation (CPB) at the Chico Mendes Institute for Biodiversity Conservation (ICMBio) to share the knowledge.

Ascensão noted in his study that nearly 200 million hectares (almost 500 million acres) of tropical forest have been lost over the past 20 years in regions where primates live. Brazil, Indonesia, the Democratic Republic of Congo, China and Malaysia account for half of this loss.

Ascensão said research already shows that these deaths and behavioral changes associated with roads, railways, power lines, pipelines and waterways severely impact primates.

“Government holds a fundamental role in orienting infrastructure development policy. It is essential that decision-makers have access to and make use of the information which those of us in the scientific community have produced,” he said. “This is the path to better-planned highways and railways, and to creating new ways of reducing existing impacts.”

Banner image of golden lion tamarins, courtesy of Sally Foster/Golden Lion Tamarin Association.

This story was reported by Mongabay’s Brazil team and first published here on our Brazil site on July 22, 2022.


Ascensão, F., D’Amico, M., & Barrientos, R. (2021). No planet for apes? Assessing global priority areas and species affected by linear infrastructures. International Journal of Primatology43(1), 57-73. doi:10.1007/s10764-021-00207-5

This story first appeared on Mongabay

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