Andy Clark/Reuters A snowy owl finds its camouflage useless in the brown grass of a marsh in Delta, British Columbia, just south of Vancouver in this 2005 photo.

An extensive survey of 903 species of Canadian birds, fish, mammals, reptiles and amphibians over more than four decades has found that half of them are in serious population decline.

Declining species lost a total of 83 per cent of their numbers between 1970 and 2014, says the report released Thursday by the World Wildlife Fund. Species protected by federal legislation shrank nearly as quickly as those that weren't.

"In general terms, the Species At Risk Act does not seem to have made any difference," said WWF president David Miller. "There's an incredible urgency to reverse the decline."

The Living Planet Index could be the most comprehensive assessment of wildlife numbers in Canada.

The organization looked at 3,689 different populations of 386 kinds of birds, 365 fish species, 106 different mammals and 46 reptiles and amphibians. It combined more than 400 datasets from government, academe, industry and citizen science using a peer-reviewed method developed by the Zoological Society of London.

There's an incredible urgency to reverse the decline.David Miller

Overall numbers for all 903 species decreased by eight per cent over the 44 years studied.

A total of 45 species were stable and 407 increased. Many of those benefited from large-scale conservation measures.

Waterfowl, which increased by 54 per cent, have enjoyed widespread wetland preservation. Birds such as falcons are no longer harmed by DDT and grew by 88 per cent.