Abstract
Avian predators readily learn to associate the warning coloration of aposematic prey with the toxic effects of ingesting them, but they do not necessarily exclude aposematic prey from their diets. By eating aposematic prey ‘educated’ predators are thought to be trading-off the benefits of gaining nutrients with the costs of eating toxins. However, while we know that the toxin content of aposematic prey affects the foraging decisions made by avian predators, the extent to which the nutritional content of toxic prey affects predators' decisions to eat them remains to be tested. Here, we show that European starlings (Sturnus vulgaris) increase their intake of a toxic prey type when the nutritional content is artificially increased, and decrease their intake when nutritional enrichment is ceased. This clearly demonstrates that birds can detect the nutritional content of toxic prey by post-ingestive feedback, and use this information in their foraging decisions, raising new perspectives on the evolution of prey defences. Nutritional differences between individuals could result in equally toxic prey being unequally predated, and might explain why some species undergo ontogenetic shifts in defence strategies. Furthermore, the nutritional value of prey will likely have a significant impact on the evolutionary dynamics of mimicry systems.
Highlights
Many insects use chemical defences in an attempt to ward off predators
We have clearly demonstrated that avian predators are prepared to eat more chemically defended prey when they are nutritionally enriched compared with when they are not
Since we have previously shown that increasing the nutrition available from alternative undefended prey decreases the ingestion of toxic prey [35], which is consistent with findings from other studies [27,28,36,37], we can be sure that predators’ increased willingness to consume nutritionally enriched number eaten
Summary
Many insects use chemical defences in an attempt to ward off predators. These defences are often combined with conspicuous warning colours and/or markings, a mode of defence known as aposematism [1,2,3,4]. We use an established system of wild-caught European starlings (Sturnus vulgaris) foraging on live undefended and defended mealworms (Tenebrio molitor) [7,14,29], where the nutritional content of the defended prey can be experimentally manipulated.
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