was the foundation of the Nearctic butterflies. Predators and avoidance Color warnings in viceroy butterflies have been shaped by natural selection in an evolutionary relationship between prey and predator. The viceroy's main predators – like many other butterflies – consist mostly of birds. Batesian mimicry The viceroy's wing color ranges from tawny orange (resembling monarchs) in the north to dark mahogany (resembling queens) in the south. It has been argued that selective pressures from predators have given rise to "model switching" in the viceroy, with each subspecies being selected to copy the color pattern of the locally dominant Danaine subspecies. When the monarch's breeding range overlaps with the viceroy, the viceroy will adopt the lighter shades of orange. Towards the south, the viceroy mostly displayed darker orange phenotypes in response to the larger population of queens. It is important to note that the differences between these two morphs is only the color of the wings and the line drawn through the viceroy's lower wings; other features, such as body size and wing-pattern elements, are identical. It had been long accepted that the viceroy practiced Batesian mimicry, with the monarch and the queen serving as models. Batesian mimicry is a type of defensive behavior in which a palatable species closely resembles unpalatable or toxic species to avoid predation. Early experiments suggested that the viceroys use Batesian mimicry to defend themselves against predators. In these experiments, birds that had not been exposed to monarchs willingly ate viceroys, but those that had tasted the unpalatable monarch refused to touch the mimic. In addition, when given the choice between a mimic and non-mimic after being exposed to an unpalatable model, avian predators never ate the viceroy mimic. The Müllerian mimicry dispute Research has argued that the viceroy may be unpalatable to avian predators. If that is the case, then the viceroy butterfly displays Müllerian mimicry, and both viceroy and monarch are co-mimics of each other. Some literature suggests that the queen-viceroy may not be a good model-mimic pair for Batesian mimicry. Experimental evidence has shown that avian predators express aversion to the queen butterfly after being exposed to viceroys. That the avian predators avoided the queen butterfly implies that the queen does not serve as a model and the viceroy as a parasitic mimic; rather, they may be Müllerian co-mimics. When avian predators were exposed to butterfly abdomens without the wings, many avian predators