Adverse effects on birds of Phosphamidon applied to a Montana forest

A field trial of Phosphamidon applied by aircraft in Montana against spruce budworm (Choristoneura fumiferana) had immediate adverse effects on birds. A 5,000-acre block of forested land was sprayed at the rate of 1 pound per acre. Some birds, including blue grouse (Dendragapus obscurus), were killed by the insecticide. Bird activity on the sprayed plot dropped to about one-quarter of the prespray level of activity while it increased on an unsprayed plot. Two sick blue grouse were caught by hand and held in captivity; one died and the other recovered. Analysis of grouse blood samples showed a marked inhibition of cholinesterase activity in the sick birds, followed by return of cholinesterase to normal in the surviving bird.