Species losing their fight for survival should be left to become extinct, if it means having resources free for other animals and plants, a survey of professional conservationists has found.

Experts are beginning to resign themselves to the idea that certain animals and plants are just too difficult to save.

A majority of the 583 experts surveyed by an academic at York University believe the time has come to consider shifting efforts away from endangered species such as pandas and tigers, to concentrate on others that have more chance of flourishing in the wild.

Questions have been raised in recent years as to whether resources on certain endangered animals could have been better spent elsewhere. The Canadian government has spent millions trying to rescue the Atlantic Salmon while the Chinese government has also poured money into trying to breed Giant Pandas, with little success.

Particularly where the loss of habitat is almost inevitable, there are serious doubts as to whether it is worth spending money trying to keep numbers up artificially, which is the case with famous endangered species - pandas and tigers. This change of heart comes in the wake of the World Bank pledging about $100 m exclusively to save the wild tiger, a generous figure that came under criticism.

Dr Murray Rudd, an environmental economist at York University, carried out the study published in Conservation Biology. He concluded that scientists now are facing the challenge in conservation is to know "what's beyond help and what's not".