A high-pitched, searing call pierced the air from behind a towering wall topped with razor wire. It was the unmistakable sound of a mountain marmoset – the buffy-tufted ear marmoset – calling from within a tiny fragment of forest hidden in the heart of the city.

We walked along the outside of the wall until we found a gate. A guard came down, unlocked it, and let us in. As we stepped through, we entered a small but magical forest, completely enclosed by the surrounding city of São José dos Campos. After 20 minutes of walking through dense vegetation, we found a group of ten beautiful marmosets, their skull-like faces and tufted ears instantly recognisable.

This small forest fragment, barely five hectares in size, was astonishingly rich in life. Orchids and bromeliads clung to trees, birds flitted through the canopy, and insects filled the air. It was a jewel of biodiversity – a refuge surrounded by busy roads, power lines, noise, and constant danger for the marmosets that lived there. Isolated and vulnerable, this pocket of forest was fighting to survive, just as the marmosets within it were.

The buffy-tufted-ear marmoset is found in south-eastern Brazil, surviving in small patches of forest in mountainous regions and, increasingly, in isolated urban fragments like this one. Their populations are now so fragmented and disconnected that very few areas support viable groups. Without intervention, these populations will continue to decline, and many will disappear entirely. In the future, these marmosets will require active management through rescue, translocation, and reintroduction into safer areas.

Here is a short video where Rodrigo Carvalho from our partners the Mountain Marmoset Conservation Programme explains plans to put a bridge over a dangerous road for the marmosets: https://www.youtube.com/watch?v=dUcQTDhrFSM

And here is a short video where I explain efforts to save the marmosets in the city of São José dos Campos: https://www.youtube.com/watch?v=1BDGwHHP_8I

The mountains of south-eastern Brazil, particularly in the states of Minas Gerais, Rio de Janeiro and São Paulo, are dramatic and biologically rich. It is high in these mountains that the the majority of populations of mountain marmosets still persist. Sadly, they are becoming increasingly threatened, primarily due to habitat destruction, with very few populations viable long term due to low numbers and isolation.

I was in Brazil with Dr Rodrigo Carvalho, who coordinates the Mountain Marmoset Conservation Programme, which we established together 10 years ago. Tom Killick from 3Ci filming also accompanied us to capture footage of this rare primate and record some of the work that is being carried out to save it.  Our aim was to join several teams in different areas who are surveying forest fragments to determine whether the marmosets still survive there and to support and help those working to find these last populations.

The two places we managed to find groups of the marmosets during our week-long search were in the isolated urban fragment of São José dos Campos and in forest high in a mountain valley near to the city of Teresopolis. Rodrigo has several groups of volunteers in different areas who regularly search for the marmosets. They play recordings of marmoset calls through speakers while walking trails in the forest. These calls will make the marmosets call back if they are in the area. They told us that some of the areas they now visit have lost their marmosets. This is what happens to populations that are so small and isolated, due to inbreeding. We visited many areas that had historical records of the monkeys but were now empty.

But there is hope. Our trip also took us to Serra Negra in Minas Gerais, at the northern edge of the species’ range. We surveyed a stunning 13,000-hectare forest that once supported mountain marmosets but now appears to have lost them, almost certainly due to yellow fever outbreaks that have devastated primate populations across south-eastern Brazil over the last decade. The forest was pristine and extraordinarily rich in plant life, yet it was strangely silent. There were no dawn calls from howler monkeys, no sounds of titi monkeys or capuchins – only the quiet of a forest missing its primates.

Local people confirmed that mountain marmosets had lived there in the past but had not been seen for many years. This makes Serra Negra a strong candidate for future reintroductions, either using animals bred in conservation programmes or individuals rescued from highly threatened fragments. So this was an intense and inspiring two weeks, focused on the survival of one of Brazil’s most beautiful and threatened primates. Meeting so many dedicated individuals working tirelessly to protect these animals gave a real sense of hope for the future. It was a trip that renewed commitment seeing firsthand the huge task ahead to save the species, and we will be doing everything we can to help secure a future for the mountain marmosets. We are very grateful to the Balcombe Charitable Trust for supporting this work.