Integrating and weighting sensory perception across modalities is crucial to how animals adapt to their environment. Divergence in brain structure is often in sensory processing regions, suggesting that investment reflects ecological needs. Here, we use two parapatric closely related species, Heliconius erato cyrbia and Heliconius himera, to test the hypothesis that divergence in sensory brain regions affects foraging decisions. These butterflies are isolated across an ecological gradient, which is linked to differences in brain morphology,...