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

Biological Journal of the Linnean Society
Wiley Blackwell (Blackwell Publishing)
Publication Date
  • Design


Abstract ‘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.

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