W. Cresswell, SURPRISE AS A WINTER HUNTING STRATEGY IN SPARROWHAWKS ACCIPITER-NISUS, PEREGRINES FALCO-PEREGRINUS AND MERLINS F-COLUMBARIUS, Ibis, 138(4), 1996, pp. 684-692
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.