The Iberian Lynx (Lynx pardinus) has a total population of only 84-143 adults, restricted to areas of Spain and Portugal, qualifying the species as critically endangered. (IUCN)

The first review of the world's mammals in more than a decade paints a bleak picture, with close to a quarter of species threatened with extinction, according to the International Union for Conservation of Nature.

The main threats are habitat loss and overexploitation for terrestrial mammals, and pollution, global warming and overexploitation for marine mammals, according to the authors of a study to be published Friday in the journal Science.

The findings, based on a survey of over 5,000 mammals on Earth, were presented Monday at an IUCN meeting in Barcelona, Spain, and are the first major update to the state of the world's mammals since 1992.

The assessment found that at least 1,141 of the 5,487 mammals on Earth are known to be threatened with extinction — or about one in five. But the authors said there is too little data to classify more than 800 mammals, many of which are thought to be endangered, bringing the estimated number of threatened species closer to one in four.

"It is frightening that after millions and millions of years of evolution that have given rise to the biodiversity of mammals we are perched on a crisis where 25 per cent of species are threatened with being lost forever," said Arizona State University professor Andrew Smith — one of more than 100 authors of the paper — in a statement.

The researchers state that 188 mammals are in the highest threat category, critically endangered, including the Vancouver Island marmot, which moved from endangered to critically endangered in the last year.

The distinction between conservation categories is a matter of degree. For example, if a decline in the animal's population is one of the measures used to assess the threat level, a critically endangered animal would be one whose population could be observed or estimated to have been reduced by 80 per cent over the last 10 years or three generations, whichever is longer.

"Our results paint a bleak picture of the global status of mammals worldwide," the authors of the Science article state. "Yet, more than simply reporting on the depressing status of the world's mammals, these Red List data can and should be used to inform strategies for addressing this crisis, for example, to identify priority species and areas for conservation."

They point to the U.S. Fish and Wildlife Service's reintroduction of the black-footed ferret to eight western states and Mexico as a successful example of conservation.