Flower use of the butterfly Maniola jurtina in nectar-rich and nectar-poor grasslands: a nectar generalist with a strong preference?

Abstract

Butterflies are often considered as opportunistic nectar consumers that visit a range of flower species. The degree of specialisation in foraging behaviour and flower choice may, however, vary considerably at the inter-specific level, from highly specialised to generalist species. In generalist nectar use, there can be intra-specific variation in the availability and use of floral resources (diversity and abundance) among different populations. Knowing the preferences of nectar-feeding butterflies can increase the understanding of ecological relationships and resource use and help in developing better strategies for butterfly conservation. By means of behavioural tracking, we identified foraging patterns of Maniola jurtina butterflies in nectar-rich and nectar-poor grasslands. For both males and females, we showed significant preference for the brown knapweed Centaurea jacea and thistles (Cirsium sp.) in nectar-rich, extensively managed grasslands. In the absence of these preferred species, as is typically the case in nectar-poor intensively managed sites, M. jurtina nectared on Trifolium pratense and Leucanthemum vulgare. Flower visits were on average shorter on T. pratense compared to C. jacea. These observational results were confirmed by a field experiment in which a wild flower nectar array with C. jacea and T. pratense was introduced. In extensively managed grasslands, foraging bouts were generally confined to patches of flowering plants and did not involve long flights between flower visits. In intensively managed meadows, butterflies performed longer flights, and ignored more flowers between two consecutive visits. Despite the variety of flower species visited, M. jurtina showed a significant preference for a few nectar sources in a context-dependent way.