Following a deadly yellow fever outbreak in 2016, brown howler monkeys are slowly making a recovery through targeted vaccination and reintroduction efforts in one of the world’s largest urban forests. The recovery is detailed in a Mongabay video by Kashfi Halford and a report by Bernardo Araujo.
Brown howler monkeys (Alouatta guariba) are endemic to the Atlantic Forest in Brazil and Argentina and were considered the primate species most affected by yellow fever, a deadly viral disease transmitted by mosquitoes of the Aedes genus.
Scientists adapted a yellow fever vaccine originally developed for humans to successfully vaccinate howler monkeys. Now, all howlers slated for translocation must be vaccinated, including those reintroduced later to the 4,000-hectare (10,000-acre) Tijuca National Park, an urban forest at the heart of Rio de Janeiro.
Located in the Atlantic Forest, Tijuca was deforested heavily to make way for housing and coffee plantations. However, after the area experienced water shortages, a reforestation program was introduced in the 19th century.
Even with reforestation, it was considered an “empty forest,” ecologist Fernando Fernandez, from the NGO Refauna, told Mongabay. Refauna was founded to rebuild the native animal life “and make this forest work again as a healthy ecosystem,” Fernandez said.
As Mongabay has previously reported, the national park has become a living laboratory for reintroductions of locally extinct species. Howler monkeys were first reintroduced in 2015, becoming the second reintroduced species to make the park their home after the agouti (Dasyprocta leporina). Both animals are excellent seed dispersers that could help regrow the damaged forest.
The initial howler population in Tijuca was a couple named Juvenal and Kala, who had a baby in 2016, Araujo reports. When the yellow fever outbreak hit, Refauna had to pause the release of howler groups into the forest. The outbreak did not affect Tijuca, and Juvenal and Kala’s family grew to six.
By 2023, more howler monkeys were brought to the park, all of them vaccinated against yellow fever. The reintroduction was challenging: An infant died from pneumonia during the group’s acclimation period and another individual was shunned by the group — she had to be returned to the Rio de Janeiro Primatology Center (CPRJ), Araujo reports.
Despite an initial cold welcome from Juvenal’s family, the new group eventually came to an understanding with the original inhabitants. Conservationists told Araujo how a newcomer howler monkey named Hope reached out to Juvenal, who accepted the touch after weeks of threatening howls between the two groups.
Less than 20% of the original Atlantic Forest remains, fragmented across much of the Atlantic coast of South America. Atlantic Forest rewilding programs like Tijuca park “have become increasingly important,” CPRJ veterinarian Silvia Bahadian Moreira told Mongabay.
Watch the documentary here. Read the report by Bernardo Araujo here.
Banner image of Max, a brown howler monkey, courtesy of Marcelo Rheingantz.
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