Testing the `Mimicry' Explanation for the Colias `alba' Polymorphism: Palatability of Colias and Other Butterflies to Wild Bird Predators

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Abstract
The naturally occurring ''alba'' morph of Colias butterflies causes re-allocation of nitrogen-rich pigment precursors away from pigmentation and into other developmental uses during pupation of its female carriers. This re-allocation has positive effects (especially at low pupal temperatures) on female emergence time, egg maturity and larval resource conservation, but negative effects on female attractiveness to males. It has been suggested that ''alba'' may also be a mimic of putatively distasteful pierine butterflies. We use wild Canada jays as experimental predators in a Colorado (USA) butterfly community to test whether two Colias, three piereine butterflies and four nymphalid butterflies differ in palatability to these birds. All species were eaten in many pairwise palatabilty trials; there is no evidence for true distastefulness of any of them. Colias and the pierines are statistically equal in percentage eaten and in percentage attacked. Colias and pierines alike are eaten somewhat less often than the most favoured nymphalid taxa. Among those trials in which both specimens were eaten, Colias were eaten first somewhat more often than the pierines. These findings are consistent with a view of the insect palatability spectrum in which Colias and the most favoured nymphalids and in which the pierines Pieris and Euchloe are slightly less preferred than Colias and the pierine Pontia. We reject the suggestion that the Colias ''alba'' variant can form a strong mimetic relationship of any sort in this community.

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