Experts said the size of a grouse population is an "indicator of the health of the Manx upland ecosystem"
A study of the Isle of Man has recommended reintroducing red grouse to boost the island's dwindling population of the bird.
The Manx Uplands report, compiled by Professor Jim McAdam, said in the past three years breeding had declined.
Research suggests the fall in grouse population was "almost entirely due to predation by harriers and peregrines".
The report said: "The size of the grouse population is an indicator of the health of the upland ecosystem."
It recommended "to at least maintain the current level of upland management and strive to increase it by a controlled and monitored reintroduction of red grouse".