Plebejus argyrognomon is one of the grassland-dwelling butterflies under rapid decline in recent decades. River bank habitats for butterfly are threatened by fragmentation, alien species, and are among the most vulnerable ecosystems. We studied the population of P. argyrognomon at the Kinugawa river bank with various plant community compositions and with different management intensities. We also tested the effect of habitat connectivity.

The results provide evidence that both host plant coverage (spring) and management intensity (summer/autumn) have positive effect on butterfly’s abundance, while nearby forest coverage, as well as plant species richness are the main negative factors. Additionally, concordant effects of habitat connectivity and nectar availability in spring and autumn suggested the lack of nectar appear to facilitate butterfly dispersal, that P. argyrognomon may occasionally move across the river.

Our findings emphasize the importance of moderate management to maintain grassland habitats for butterfly on river banks, which may also contribute to the conservation of other grassland-dwelling butterflies in fragmented landscape.