Birds learn to avoid aposematic prey by using the appearance of host plants

Callum Mclellan*, Nicholas E Scott-Samuel, Innes C Cuthill

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review


The conspicuous warning signal of aposematic animals is learnt by their predators, the resulting avoidance benefiting both parties1,2,3,4. Given evidence that birds can distinguish the profitability of prey from the environmental context in which they appear5, aposematic insects’ host plants might also provide an important cue to foraging predators6. The aposematic cinnabar moth (Tyria jacobaeae) larva is a specialist on its ragwort (Senecio spp.) host plant7, presenting a consistent environment with which it could be reliably
associated. Additionally, ragwort’s defensive toxins prevent non-specialist, profitable insects from feeding on it8. Thus, avian predators may recognise cues from ragwort, most likely its conspicuous yellow flowers9,10, and use this information to avoid cinnabars. To test this hypothesis, we exposed artificial cinnabar and non-signalling ‘caterpillar’ targets to wild avian predation by presenting them on ragwort and non-toxic host plants. We also manipulated the
presence or absence of ragwort flowers on hosts. In doing so, we show that both targets are better protected on the cinnabar’s natural ragwort host and that birds use ragwort’s distinctive yellow flowers as the cue to avoidance. Additionally, we found that naïve predators do not make prey host foraging distinctions, indicating that this avoidance behaviour is learnt through experience. Our findings are among the first to suggest that a host plant’s features act as an extended phenotype that signals the toxicity of the prey which live on it. This prey-host relationship may facilitate the initial evolution of toxicity in nonsignalling prey, but also inhibit the evolution of aposematic signals themselves.
Original languageEnglish
JournalCurrent Biology
Publication statusAccepted/In press - 17 Sep 2021


  • Aposematism
  • warning signals
  • avoidance learning
  • extended phenotype
  • host plant
  • chemical defence


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