Analysis of the Kestrel's (_Falco tinnunculus_) predatory behaviour toward rodents

The predatory behaviour of the Kestrel (Falco tinnunculus) was investigated in detail. I focused particularly on the behavioural sequence displayed by the raptor when catching the prey, the technique used to capture and kill the prey itself, and the causes of death. Although many researchers have been studying the predatory behaviour for several decades and from different points of view, little is known about the killing method. Previous studies by the author suggested that the prey (a mouse) received repeated bill pecks, particularly on the head region, but that talons were apparently not used at all. It was then hypothesized that death was caused by suffocation and not by the possible wounds. The tests were performed in captivity in a 4.30 x 2.60 m aviary equipped with a perch and a small table in the middle, where the prey was put for the test. The aviary was located at the Raptor Recovery Centre of Parma, managed by L.I.P.U. All the seven Kestrels used were wild individuals. They were tested when in good condition, at the end of the recovery period and immediately before release. The birds were tested individually and were offered a prey that was alternately a laboratory mouse (Mus domesticus) of 12-15 g and a laboratory rat (Rattus norvegicus) of 48-60 g, in order to maintain a body weight ratio of 1:4. Such a difference could show variations in the use of pecks and talons in relation to the size, and thus strength, of the prey. In fact, it was expected that the pecks would be more frequent against the bigger prey in order to counteract its greater struggle to escape, and that the talons would be used with equal frequency for killing or, possibly, with lower frequency against the mouse, the smaller prey. The rat received a much higher (P < 0.001) mean frequency of pecks than the mouse (37.2 ñ 5.8 vs 5.2 ñ 0.8) suggesting that the they are used principally as an aid for prey blocking. In fact, the pecks were mostly directed against the base of the head and the ocular region. By damaging the central nervous system they help to reduce further movement and attempts to escape, particularly when a large and strong prey is caught. Moreover, when the Kestrel preyed upon the rat, it took a significantly (P < 0.001) longer time to begin ingestion (302.7 ñ 75.1 vs 58.3 ñ 7.0). During that period, the bird remained almost motionless, except for the occasional bill pecks, and never lost contact with the prey, continuing instead to clasp it with the foot. The duration is probably because the rat died more slowly, and is indirect evidence that the Kestrel used only foot pressure and not the talons to kill its prey. Sometimes the prey (15 mice and 13 rats) was removed after death and before ingestion, in order to carry out a necropsy. Such analysis revealed only one animal with a superficial wound from talons. In contrast, clear evidence of alterations related to suffocation were always recorded: large pleural petechiae, enlargement of coronary arteries, prolonged blood fluidity. In conclusion, the behaviour of Kestrels after catching prey is clearly influenced by the prey size. The absence of talon use is confirmed and moreover the killing technique does not seem to be as specialized as is the capture technique