An Experimental Study of Migration in the Glanville Fritillary Butterfly Melitaea cinxia

1. We studied factors affecting emigration and immigration behaviour in the butterfly Melitaea cinxia by releasing 882 newly emerged marked butterflies into 16 habitat patches in a network of 64 empty patches on an isolated island (area 1.6km2). 2. Of the 363 butterflies that were recaptured at least once, 40% were recorded in a new patch during their lifetime. Females emigrated earlier and moved further away than males. One-third of males appeared to remain permanently in, whereas females gradually drifted away from, the release patch. 3. High density of butterflies, great abundance of flowers, and large patch area decreased emigration, whereas open landscape around the patch increased emigration. Females that emigrated were on average larger than females that stayed in the patch of release. 4. In total, 152 immigrants were recorded in 32 patches. Numbers of immigrants increased with patch area and abundance of flowering plants. 5. Results on emigration suggest that conserving an isolated butterfly population is more successful in an area with physical barriers to migration than in an open landscape. The possible tendency of butterflies to leave a patch with low density should be taken into consideration in introductions of butterflies to empty habitat patches. 6. Results on immigration indicate the significance of nectar sources and patch size in successful colonization of empty habitat patches.