Supporting data for "Multi-species winter aggregation and movement patterns of danaid butterflies (Lepidoptera: Nymphalidae: Danainae) in Hong Kong"

Danaid butterflies (Nymphalidae: Danainae) in Asia form aggregations and/or exhibit migratory flights similar to those of the migratory monarch (Danaus plexippus) in North America. In contrast to the well-studied single-species system in their threatened relative, however, tropical and subtropical Asian danaids form smaller multi-species aggregations and show seasonal movements of which we understand little. In this study, we used publicly reportable stickers to tag 15,918 danaid butterflies from 13 species and five genera (Euploea, Tirumala, Danaus, Ideopsis, Parantica) over four years in Hong Kong to elucidate patterns of seasonal aggregation and movements. Through mark-recapture data, we estimated up to 16,000 butterflies in single aggregation, where aggregations differed in species assemblages at forested valleys versus open sites rich in pyrrolizidine alkaloid (PA) plants. Recoveries of 1,503 tags (50.6% reported by the public) revealed local movements of 78 individuals, but no butterflies were reported outside Hong Kong. The observed variation in aggregation dynamics and movement patterns indicate interspecific differences in site selection, overwintering strategies, and orientation of seasonal movement. Regional collaboration across southern China and the Indochinese region is necessary to understand these complicated patterns and inform the conservation of sensitive overwintering and migratory phenomena.