One Falco rusticolus and two of 24 Falco peregrinus were positive for Plasmodium relictum. Sixteen percent of the erythrocytes (RBC) of the gyrfalcon were parasitized. Following treatment with chloroquine the parasite burden was dramatically reduced (to less than 0.01%). Infection in peregrine falcons was low (0.01–0.4% RBCs were parasitized). This is the second report of Plasmodium in the gyrfalcon and the first report in the peregrine falcon.
