Peregrine falcon and merlin predation on small shorebirds and passerines in Alberta

This study describes and compares hunting techniques and predatory efficiency of peregrine falcon (Falco peregrinus) and merlin (Falco columbarius) preying on small shorebirds and passerines in open agricultural lands around Beaverhills Lake, Alberta, during spring and fall, 1965–1987. Hunting methods were divided into four categories: (i) surprise attacks with less than six swoops at prey initially on the ground, (ii) short pursuits with less than six swoops at flying prey, (iii) persistent, long-range pursuits with more than six swoops, and (iv) other or unknown methods. They made up, respectively, 73.9, 17.2, 2.5, and 6.4% of 647 hunts by peregrines, and 72.3, 16.1, 4.5, and 7.1 % of 354 hunts by merlins. Persistent pursuits of prey were significantly more successful than surprise attacks by merlins (62.5 vs. 9.4%, P < 0.00001), but not by peregrines (18.8 vs. 8.8%, P = 0.40). I postulate that peregrines and merlins employ persistent hunting techniques only if surprise attacks are unproductive because of (i) lack of expertise of the falcon, (ii) scarcity of prey, (iii) unsuitable habitat, and (iv) effective early warning by flocking prey. Peregrines captured 50 shorebirds of 11 species, and 3 passerines of 2 species. Merlins captured 28 shorebirds of 8 species, and 16 passerines of 5 species. Adult male merlins were significantly more successful than immatures and adult females combined (38.7 vs. 9.1%, P < 0.00001). Adult peregrines were not significantly more successful than either spring or fall immatures (9.2 vs. 7.2 and 4.9%, P = 0.21, P = 0.24, respectively). Merlins were significantly more successful than peregrines in hunting small passerines (12.2 vs. 3.8%, P = 0.04), but not significantly more successful in hunting small shorebirds (12.6 vs. 8.8%, P = 0.10).