Tendon locking
Tendon locking is used by many animal species which sleep in trees or caves. It lets them sleep without falling off. The system has evolved separately in a number of vertebrates, so it is an example of parallel evolution.
Bird feet[change | change source]
The leg arrangement of passerine birds has a special adaption for perching: a tendon-locking mechanism. A tendon in the rear of the leg is automatically pulled and tightened when the leg bends. This makes the foot curl stiffly round when the bird lands on a branch. The tendon is locked in place by another tendon. So passerines sleep while perching without falling off.[1][2]
Small mammals[change | change source]
Small animals which sleep in trees or caves usually hang on with their feet: they have a tendon locking device which keeps them hanging on even during sleep.[1][3][4] It works by one tendon running down the leg shifting position slightly so it grips the tendon which closes the toes. Bats independently evolved a similar arrangement.[5] Once the tendons are locked, the muscles in their legs and feet can relax.[6] Even dead bats stay hanging.[7] These various examples have evolved independently of each other: this is known from the fine details of the mechanism. One plus of a locking mechanism is that it allows attachment to slender branches on which predators might be unable to walk.
Linking behaviours[change | change source]
There are various group behaviours which supplement the effect of tendon locking. The most obvious is complete silence. Starlings migrate in large groups, and they can go from making a huge noise to complete silence after landing on an overnight roost.
References[change | change source]
- ↑ 1.0 1.1 Stefoff, Rebecca 2008. The bird class. Marshall Cavendish Benchmark.
- ↑ Brooke, Michael and Tim Birkhead 1991. The Cambridge Encyclopedia of Ornitholigy. Cambridge University Press.
- ↑ Brooke, Michael & Birkhead, Tim 1991. The Cambridge Encyclopedia of Ornithology. Cambridge University Press. ISBN 0521362059
- ↑ Simmons N.B. and Quinn T.H. 1994. Evolution of the digital tendon locking mechanism in bats and dermaptorans: a phylogenetic perspective. Journal of Mammalian Evolution. POI: 10.1007/BF 01464276 [1]
- ↑ Quinn T.H. & Baumel J.J. 1990. Chiropteran locking mechanisms: the passive digital lock. J. Morphology. 109, 281–208.
- ↑ Haffner M. 1966. A tendon locking mechanism in two climbing rodents. Journal of Morphology 229, 197–227.
- ↑ Where do bats live? University of Edinburgh Natural History Collection [2] Includes useful diagram