Kleptoparasitism of Barn Owls by Common Kestrels is not that uncommon, I have seen it twice this winter at a site in Cambs. Its common enough in Short-eared Owls that someone got enough data to relate the occurrence to concurrent weather conditions: Wind speed as a determinant of kleptoparasitism by Eurasian Kestrel Falco tinnunculus on Short-eared Owl Asio flammeus:
http://www.jstor.org/pss/3677118 Try doing a google scholar search for food piracy in raptors, e.g.
http://scholar.google.co.uk/scholar?hl= ... +piracy%22British Birds 88:10, 485-487:
Common Kestrel robbing female Eurasian Sparrowhawk
On 3rd November 1992, in a meadow near Halfweg, a village west of Amsterdam, Netherlands, I saw a female Eurasian Sparrowhawk Accipiter nisus catch a Common Starling Stumus vulgaris on the ground. The latter uttered loud distress calls while the Sparrowhawk sat on it. Suddenly, a Common Kestrel Falco tinnunculus appeared, uttering an aggressive cry. A brief quarrel ensued on the ground. The Kestrel, probably a female (events happened too rapidly to be certain), grabbed the Starling, still alive, from the hawk's talons and flew off with it.
Mostly during the last 25 or so years, several notes have been published in British Birds on Common Kestrels robbing other avian predators. The victims of these robberies were: Short-eared Owl Asio flammeus (64: 317; 66: 228; 67: 474-475; 85: 188); Barn Owl Tyto alba (61: 264; 72: 337); Little Owl Athene noctua (40: 216); Merlin F. columbarius (72: 336-337); and Eurasian Sparrowhawk, a male robbed of its small-mammal prey in flight (70: 35-36). My observation shows that a Kestrel was able to rob a much larger female Sparrowhawk without much difficulty.
Joh. J. Frieswijk
Gerard Terborgstraat 51 III, 1071 TL Amsterdam, The Netherlands EDITORIAL COMMENT The importance of food-robbery by other raptors in the evolution of the eating behaviour of Eurasian Sparrowhawks is discussed in The Sparrowhawk (Ian Newton, 1986, pp. 107-110).
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Dr Alexander C. Lees
Lecturer in tropical ecologyManchester Metropolitan University
Lab Associate
Cornell Lab of Ornithology,
Cornell University
http://www.freewebs.com/alexlees/index.htm@Alexander_Lees