High warning colour polymorphism in Heliconius hybrid zone roosts

1. Communal roosting behaviour has been documented among a wide range of taxa, particularly among groups of butterflies that display warning colourations. These aggregations of conspecifics and/or other species that share mimetic warning colour patterns can have a large impact on predator learning, and thus the survival of an aposematic form. Yet there has been limited investigation of communal roosting within areas where new and diverse warning colour forms are generated, such as hybrid zones. 2. Here, roosting behaviour was examined in a Heliconius erato hybrid zone in French Guiana between races with divergent warning colourations on their wings. In this hybrid zone, native individuals with nine distinct warning colourations, as well as individuals with altered forms that are not native in the French Guiana population, were marked and observed to determine if divergently coloured individuals participated in communal roosting, and if the proportions of colour pattern forms at roosts differed from the proportions that are found in the population. 3. The results demonstrated that divergently coloured individuals of the same species, including altered, non‐native forms, will readily and repeatedly participate in nocturnal communal roosting, often with extreme fidelity to specific perch locations. 4. These findings suggest that roosts composed of polymorphic warning patterns may be common in phenotypic transition zones, which could have major implications on predator training and selection dynamics in hybrid zones.