Adaptive details in the comparison of predatory behaviourw of four owl species

Abstract

The predatory behaviour of four owl species, tawny owl (Strix aluco), long-eared owl (Asio otus), little owl (Athene noctua) and barn owl (Tyto alba), was compared. The birds were wild individuals temporarily in captivity for rehabilitation and were tested before release into an outdoor pen. Between four and ten birds per species were individually tested by offering a laboratory mouse used as prey. The resulting sequence of the predatory behaviour patterns was homogeneous among the species. The latency to attack was similar and there was a tendency to prefer direct attacks, i.e. landing onto the prey directly, instead of indirect ones, i.e. landing a few centimetres from the mouse. However, tawny owls used the former attack only. The various degrees of specialisation to hunt small mammals is reflected by the grip location: the barn owls strongly preferred to seize the mouse on the head, while the little owls preferred the trunk and the other species preferred either location. Similarly, after grasping the mouse tawny and long--eared owls struck it with the beak, while the little owls performed strikes similar to bites. In contrast, barn owls performed a peculiar torsion of the neck region, instead of a beak strike. We interpret this pattern difference within a basically homogeneous behaviour sequence as evolutionary radiation due to species-specific specialisation of feeding and hunting behaviour.

Bird claws and bird of prey talons: Where is the difference?

“…We dealt with the right foot only and, particularly, with measurements of toe and claw of toe-1 and toe-3, as they are the shortest and the longest toe, respectively. Such a decision was justified by considering that toe-1 and toe-3 are the most important toes to grip a branch or, in the case of raptorial species, to grip prey (Goslow 1971;Csermely et al 1998Csermely et al , 2002, as they are in opposition to each other. The measurements were made using a digital caliper (Borletti, Switzerland) measuring to the nearest 0.01 mm.…”

Comparison of claw geometrical characteristics among birds of prey and non-raptorial birds

“…Such a decision was justified by considering that toe-1 and toe-3 are likely the most important toes to grip a branch in arboreal species or, in the case of raptorial species, to grip the prey (Goslow 1971;Csermely et al , 2002, as they are in opposition to each other. Nevertheless, both Einoder & Richardson (2007a) and Fowler et al (2009) are of different opinion because they point out that it is not always true, as they demonstrated that Accipitridae have hypertrophied toe-2 claw.…”

“…Their zygodactylous grip is likely an adaptation to maximize the grasping area and to increase strength during grasp, therefore allowing owls to subdue proportionally larger prey, as small mammals are in comparison to their predators (Ward et al 2002;Einoder & Richardson 2007a). The above claw and toe condition also is an indirect indication of the Strigiformes use of claw to encircle the prey rather than using it as a weapon to kill (Csermely et al , 2002.…”

“…That is particularly useful because toe-1 tends to press the ventral surface of a ground-dwelling prey, e.g. a small mammal, helping to press the lungs for getting death by suffocation (Csermely & Gaibani 1998;Csermely et al , 2002. Strigiformes also have a less hooked shape claw in relation to its radius than Non-raptorials in both toe-1 and toe-3 (cf.…”

“…This is likely an adaptation for squeezing the prey tightly to induce death (Csermely et al , 2002. Strigiformes have a very pronounced movement of distal phalanx, which can be easily turned as in a much closed grip.…”