Over 5,500 species of birds, mammals, reptiles and amphibians are subject to legal and illegal trade around the world. This represents 18% of the vertebrate species of the earth. This figure is higher than previous estimates, according to a study published in the scientific journal Science, BTA reported.

Roughly one of every five animals that walks the land or plies the skies is traded internationally, the research notes.

The most affected species are often also the most vulnerable or threatened with extinction, say the study's authors - scientists at the universities of Florida and Sheffield.

27% of mammals’ species are affected  for the purpose of extracting products from them, such as the case of pangolins killed for their flakes and meat. Reptiles and amphibians are often sold as pets or for zoos, circuses and exhibitions. 23 percent of the bird species are bought and sold for both domestic animals and for the extraction of products for the purpose of medicines or trophies.

According to researchers, the number of affected species is 40-60 percent higher than in previous studies. Experts predict that in the future, legal and illegal trade will add between 317 and 3196 species to the list, mainly species close to those already hunted or relatively large animals that are most valued.

The researchers concluded that more than 8,000 wild species might eventually be included in the global wildlife trade market—3,000 more than are now. The new total would encompass almost 30 percent of all mammals, birds, amphibians, and reptiles, National Geographic reported.

Abundant species are not necessarily protected. The species is often added to the protection lists after a significant decline in its population, scientists say.

At the same time, the Ministry of the Environment of the Republic of South Africa announced the seizure of 340 kilograms of lion bones, France reported. Three people were arrested. The bones were in crates destined for Malaysia. They are used for medical purposes or for the production of jewellery.

More than 11,000 lions live in Africa, 3,000 of which are freed in national parks. International trade in parts of lions killed in the wild is prohibited by international treaties, but authorized for captive animals. However, the export of these parts requires a special permit.