Story highlights Report: Wild giraffe population falls 40% in 30 years

Birds, insects, aquatic life and plants also join "red list"

(CNN) Africa's wild giraffe population has plunged dramatically and the world's tallest animals are in the process of a "silent extinction," a conservation group has reported.

Giraffe populations have fallen by up to 40% over the last 30 years, the International Union for Conservation of Nature says in the latest edition of its "Red List" of endangered species.

The gentle giants' numbers have dipped from as many as 163,000 in 1985 to just over 97,000 last year, according to the report.

The steep decline was one of the headline statistics from the report, and is driven by "habitat loss, civil unrest and illegal hunting," it states. Elsewhere, of the 742 newly recognized bird species in the list, 11% are considered threatened -- and 13 already listed as "extinct."

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"Many species are slipping away before we can even describe them," IUCN Director General Inger Andersen said in response to the report's publication. "This IUCN Red List update shows that the scale of the global extinction crisis may be even greater than we thought."

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