BARCELONA, Spain (CNN) -- Nearly a fourth of the world's mammals are threatened with extinction, a leading international conservation group said Monday as it unveiled its latest global study of the problem.

Climate change is affecting sea ice-dependent species such as polar bears.

At least 1,141 of the 5,487 mammals on Earth, or 21 percent, are endangered species, the International Union for Conservation of Nature (IUCN) said at the start of its World Conservation Congress in Barcelona.

The problem appears to be getting worse since the IUCN's last comprehensive survey of mammals 12 years ago, the IUCN's Jan Schipper told CNN. But he added that more study will be needed in the coming months.

The IUCN, in updating its trademark Red List of Threatened Species, emphasized that conservation efforts could help turn the tide.

"Hundreds of species could be lost as a result of our own actions, a frightening sign of what is happening to the ecosystems where they live," Julia Marton-Lefevre, IUCN's Director General, said in prepared statement. "We must now set clear targets to reverse this trend."

The IUCN study also showed that 5 percent of the mammals currently listed as facing possible extinction are showing signs of recovery in the wild. And just 76 mammals have become extinct in the last 500 years, the IUCN said.

But the study said 188 mammals are critically endangered, including the Iberian Lynx, which has at most 143 adults remaining. They are on a steady decline mainly because there's a shortage of their primary prey, the European Rabbit.

Another 29 species were listed as critically endangered and possibly extinct, such as Cuba's Little Earth Hutia, which has not been seen in 40 years, the IUCN said.

The Swiss-based IUCN, founded 60 years ago, has a membership of more than 80 nations and 800 non-governmental agencies like environmental groups, and also counts on 11,000 volunteer scientists around the globe.

The latest study citing the danger to mammals involved 1800 scientists in 130 nations. It showed that China's "Pere David's Deer," already listed as extinct in the wild, is showing signs of recovery in captivity and that relaunching it in the wild may soon be attempted.

Schipper said that although the study put 21 percent of the world's mammals on the endangered list, it might be as high as 36 percent, pending further study, particularly for 836 mammals for which scientists still have little incomplete information.

The new study is far more comprehensive than the last major study in 1996, and includes 700 more mammals, IUCN officials told CNN.

Enhanced study methods and tracking of mammals and other species -- marine species, plants and insects -- has increased dramatically since 1996, which makes it hard to compare the current results with those of 12 years ago, Schipper said.

In just one example, Schipper said, the lemur, a primate in Madagascar, was thought to have been just one species there in 1996, but further study has shown three different species of lemurs, separated by rivers or valleys.

The IUCN said the loss or degradation of natural habitats is affecting 40 percent of the world's mammals, particularly in Latin America, much of Africa and in southeast Asia. Overharvesting is wiping out larger mammals in many locations.

Overall, the IUCN Red List now includes 44,838 species of all categories -- mammals and other species -- of which 38 percent are threatened with extinction.

Nearly a third of amphibians alone face extinction or have already become extinct, the IUCN said.

Barcelona's zoo has a number of mammals on the endangered list, including the Chimpanzee, Red Panda, Variegated spider monkey, Sumatran Tiger and African hunting dog, zoo and IUCN officials told CNN.

The zoo -- not far from the IUCN congress that has brought thousands of government officials, environmentalists and scientists to the city for the conference which is held every four years -- has made conservation of endangered species a key part of its work, zoo officials told CNN.