SURPRISE AS A WINTER HUNTING STRATEGY IN SPARROWHAWKS ACCIPITER-NISUS, PEREGRINES FALCO-PEREGRINUS AND MERLINS F-COLUMBARIUS

Sparrowhawks Accipiter nisus, Peregrines Falco peregrinus and Merlins Falco columbarius were studied hunting Redshanks Tringa totanus, Dunli ns Calidris alpina and Skylarks Alauda arvensis over three winters on a small Scottish estuary. Most Sparrowhawk and Merlin hunts consisted of a single attack (mean = 1.0 and 1.1, respectively), whereas Peregri ne hunts often consisted of several attacks (mean = 1.8), Most hunts w ere short (<1 min), but Peregrine and Merlin hunts occasionally lasted over 5 min, In general, all three raptor species attacked by surprise , although Peregrines were more likely to make nonsurprise attacks. Pr ey attacked were usually initially very close to the raptor (<100 m); Peregrines attacked prey most often at long distances (>500 m). Chase lengths were mostly <5 second in length, although Peregrines, and part icularly Merlins hunting Skylarks, often chased for several minutes. P eregrines attacked most prey in flight from night, while Merlins and S parrowhawks attacked birds on the ground with a flight from a perch, A ll three raptor species preferentially attacked larger Dunlin necks, b ut Peregrines also favoured single birds, Capture rates of Redshanks a nd Dunlins were similar for the three raptor species (C, 10%), but for Skylarks, capture rate by Merlins was much higher (12%) than by Sparr owhawks (3%) or Peregrines (0%), Capture rates were highest when rapto rs attacked by surprise, particularly for a Peregrine hunting in the f irst minute of arrival on the study site if no Peregrines had been hun ting there for the previous hour (16% success for the first minute com pared with 2% in subsequent minutes), Sparrowhawks were more successfu l when attacking small rather than large Dunlin necks. The use of shor t surprise attacks interspersed with long periods of inactivity was co mmon to the three raptor species and was interpreted as a strategy to minimize the amount of energy and risk involved in hunting during the nonbreeding season.