Sydney scientists are feeding toad snags, which are laced with a mild chemical that induces nausea, to endangered animals to train them to avoid eating the toads.

Rick Shine, of the University of Sydney, said most animals learnt pretty quickly not to eat the highly poisonous amphibians. But bigger predators such as quolls, goannas and snakes could not resist a tasty toad, which had reduced some local populations of the species by up to 90 per cent. ''The toad toxin kills animals by stopping their heart but it doesn't make them feel sick,'' he said.

Professor Shine and his team thought if they could train vulnerable animals that toads taste bad, and associate them ''with feeling nauseous and miserable'', they may learn to avoid them. ''When I was 18 years old I drank far too much scotch one night, I couldn't touch scotch again for about 30 years and I still don't like it.''

He said the same phenomenon, known as taste-aversion, could affect other animals.

An honours student, Stephanie O'Donnell, fed captive-bred quolls dead baby cane toads laced with a tasteless, low toxicity chemical. When released in the Northern Territory the quolls avoided the toads and survived.