Giraffe numbers have declined by as much as 40 percent since the 1980s in a "silent extinction" driven by human causes, the International Union for Conservation of Nature (IUCN) reported on Thursday. The Red List of endangered species complied by the IUCN moved the giraffe to the category "vulnerable" to extinction for the first time, against a previous rating of "least concern". Populations of the world's tallest land creature fell to about 98,000 in 2015 from an estimated 152,000-163,000 in 1985, according to the list compiled by the IUCN.