Cuttlefish camouflage: a quantitative study of patterning

To investigate camouflage design, we compared the responses of two species of cuttlefish ( Sepia officinalis and Sepia pharaonis ) with controlled but naturalistic backgrounds, consisting of mixtures of 1-mm and 9-mm diameter coloured pebbles. Quantitative analysis of image data using methods adapted from functional imaging research found differences in how the two species camouflage themselves. Whereas S. officinalis switches from background resemblance to a disruptive pattern as it moves from a fine to a coarsely patterned background particle, S. pharaonis blends the two types of pattern. We suggest that the differences may arise because S. pharaonis needs to produce camouflage that is effective when viewed over a relatively wide range of distances.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 335–345.     

Fast movement of densely aggregated prey increases the strength of anti-apostatic selection by wild birds

'Anti-apostatic' selection occurs when predators preferentially remove rare forms of prey, and has been demonstrated in both static (artificial) prey and moving (natural) prey. We performed 24 experiments at separate sites to test the effect of prey mobility on the strength of anti-apostatic selection by wild passerine birds. The prey were yellow and red Calliphora maggots and were presented in 9: 1 and 1: 9 ratios on a specially designed bird table. The temperature of the maggots, and hence their speed of movement, was adjusted by a combination of the ambient temperature and a candle under the bird table. Selection was anti-apostatic at all three classes of temperature and was strongest at the highest. We conclude that anti-apostatic selection on static prey is enhanced when they are made to move–possibly because the 'confusion effect' caused by the moving prey makes the birds concentrate more strongly on the rarer colours.