Nevertheless, within this relatively short timeframe, eight of the 17 populations were seen to fall markedly in size - some by more than 90% - with only one showing any sign of a rise.
Species in decline include the asp and the smooth snake from Europe, the Gabon viper and rhinoceros viper of West Africa, and the royal python
Populations shrank even in protected areas, suggesting that the progressive loss of habitat for wild animals being seen all over the world is not the only cause.
Similar steep declines observed in frogs and newts in an earlier period were eventually found to be caused by the fungal disease chytridiomycosis.
The year when many of the snake declines began - 1998 - raises the question of whether climatic factors might be involved, as very strong El Nino conditions contributed to making it the hottest year recorded in modern times. FULL STORY