Treecreeper Climbing; Mechanics, Energetics, and Structural Adaptations

Abstract

The mechanics and energetics of tail-supported clinging and climbing by Certhia familiaris on vertical trunks were analysed from still photographs and cine films. A complete movement cycle, or stride, consists of the power stroke and a floating phase. One stride analyzed in detail was 66 mm long and took 0.1375 s. The bird moved about half the stride length in the power stroke which took about 0.0625 s. In the beginning of a stride the bird accelerates with 20 m s-2 (= 2 g), and the feet exert a force on the trunk about 3.2 times the bird weight Mg. Its maximum velocity is about 1 m s-' vertically upwards and 0.24 m s-' horizontally towards the trunk. The energy cost of one stride is 0.028 J, and 84% of this is for moving vertically upwards, while the rest goes to moving horizontally (6%), moving the legs (5.6%), and rotating the body and head (4.4%). The metabolic power due to work done in a stride is 0.2 W, which is 0.91 the basal metabolic power BMP. During foraging the bird climbs 0.1 m s-', and has a stride frequency of 1.5 s-', and a power output for locomotion of 0.043 W, or 0.19 BMP. The strong claw curvature, long hind-claw, and graded length of fore-toes are adaptations to climbing. Factors are considered which affect optimal tail length in tail-supported trunk-climbing birds. Certhia has a longer tail in relation to body size than have woodpeckers, a difference related to differences in locomotor habits.