The International Union for Conservation of Nature lists black lion tamarins as Endangered (IUCN, 2020), appearing on the IUCN Red List of Threatened Species. This designation is due to a predicted population loss of more than 50% over the next twenty years, or about three generations. There are only an estimated 1,600 remaining mature black lion tamarins alive today, living in just 15 forest patches. Only one of these subpopulations, the 1,200 black lion tamarins in Morro do Diabo State Park, is considered “viable” by scientists, meaning that it has enough individuals—at least 750, according to researchers—to retain enough genetic diversity for the species. Populations that are too small do not have the genetic diversity to survive in the long-term. The other 14 subpopulations all have fewer than 80 animals and live on less than 6,000 acres (2,400 ha). These subpopulations are not expected to survive in the long term, and may even be extirpated—or locally extinct—by 2050.

Further habitat loss of 10–15% by 2040 is expected, and the already small black lion tamarin subpopulations will become even more fragile. Of particular concern are “stochastic events.” These are unpredictable events, such as extreme weather or disease outbreaks, that can significantly harm populations. The smaller and more disjointed a population is, the more harm these stochastic events can do. For example, an outbreak of yellow fever beginning in 2018 resulted in the deaths of one-third of wild golden lion tamarins, the closest living relatives of black lion tamarins. Low genetic diversity can play a role in a species’ susceptibility to these stochastic events as well. If a species has low genetic diversity, all or most of its individuals may be vulnerable to a particular disease, like “putting all your eggs in one basket,” as the saying goes. A more genetically diverse population will have more individuals that are resistant to the disease, so they are more resilient to these events.

Compounding all these issues is climate change. Models show that climate change will shift suitable black lion tamarin habitat southwards in the coming decades and result in an overall reduction in suitable black lion tamarin habitat of 28%. As the climate changes and suitable habitat shifts southwards, black lion tamarins will need to follow that shift and move south. But because black lion tamarins live in “islands” of forest, there is presently no viable way for them to make that move. Unless a network of habitat corridors is created, the black lion tamarins will have nowhere to go and will be left in unsuitable habitat as the climate changes. This will spell disaster for the species unless significant conservation efforts are undertaken. One model shows that black lion tamarins will be exposed to these climate impacts within 60 years.