The nature of migration in the red admiral butterfly Vanessa atalanta: evidence from the population ecology in its southern range

1. The migrant Vanessa atalanta (L.) occurs throughout Europe and North Afr ica. In autumn, populations emigrate from northern and central Europe to th e Mediterranean region to overwinter. In the spring, the northern range is recolonised by migrants from the south. The dynamics of the species in the winter range is poorly known. 2. From 1994 to 1999, adults and immatures of V. atalanta were monitored al l year round in Mediterranean habitats in north-east Spain. 3. Data showed that the Catalonia lowlands is an area to which V. atalanta migrates to breed during the winter. Migrants arrive in October and early N ovember and initiate a period of intensive breeding. Larval development occ urs throughout the winter until a first annual generation of adults appears in early spring. 4. Most of the butterflies emerging in the spring emigrate and leave the ar ea without breeding. The data suggest strongly that recolonisation of the n orthern range is by these butterflies not by wintering adults. Altitudinal migration also seems to be a common phenomenon, allowing a further summer g eneration of adults to occur at high elevations within the Mediterranean re gion. 5. The complex phenology of V. atalanta in its southern range has evolved a s a strategy to track larval resources through space and time. Autumn migra tion coincides with the greatest availability of the main food plant, Urtic a dioica L. Late spring migration occurs by the time food quality is decrea sing.