Evidence for a more effective signal in aggregated aposematic prey

Aposematic prey tend to live gregariously. A recent study using artificial prey has shown that a gregarious life style can be advantageous by generating faster avoidance learning in predators (Gagliardo & Guilford 1993, Proc. R Soc. Lond. Ser. B, 286, 149-150). However. a predator may react differently to artificial and live prey. This study investigates whether chicks, Gallus gallus domesticus, react differently towards aggregations and solitary individuals of the seed bug Spilostethus pandurus (Heteroptera: Lygaeidae). There was no significant difference in the speed of avoidance learning between chicks presented with grouped prey and chicks presented with solitary prey. The aggregated prey did, however, generate greater unconditioned aversion than prey presented singly. This indicates that a possible advantage of grouping in aposematic prey is a more effective aposematic signal. The greater unconditioned aversion is comparable to the generally greater initial reluctance of predators to attack aposematic than cryptic prey. (C) 1996 The Association for the Study of Animal Behaviour