Prof Phil Bishop discussed the integral role frogs play as indicators of the health of ecosystems, at a public lecture at the Dunedin Botanic Garden on Friday.
Of the 6647 species of frogs around the world, about 43% faced the risk of extinction, he said.
Habitat change, pollution and disease meant frogs had more chance of disappearing than birds and mammals combined.
New Zealand's native frogs faced as much chance of extinction as those in other parts of the world, Prof Bishop said.
"New Zealand frogs are all very endangered and live in fragmented populations.''
The use of chemicals posed a particular threat to the frogs.
"Herbicide causes chemical femalisation of all invertebrates.
"And at a very, very low concentration.''
About 5000 tonnes of the chemical was used in New Zealand each year, he said.
Frogs were the ``global canaries of the coalmine''.
"Because of their sensitive skin, when frogs start to decline we know the ecosystem is in a terrible state.''
They were also valuable in biomedical research and played a crucial role in the food chain.
"Frogs eat insects and birds eat frogs.
"If the frogs are gone, birds and reptiles have to eat insects, which they are not very good at.''
People could help protect the future of frogs by living in a sustainable way, he said.
"Clean water and clean environments will make the difference.''
