Evidence for hilltopping in bumblebees?

Abstract

1. Male bumblebees are known to exhibit a range of mate-location behaviours, including perching on prominent objects and darting at passing queens, patrolling of scent-marked flight routes, and waiting outside nest entrances for virgin queens to emerge. Here we provide evidence for a fourth strategy, known as hilltopping. This behaviour is widely known from a range of invertebrates, but has not previously been described in bumblebees. 2. We studied the distribution of bumblebees along transects ascending four hills in Scotland and demonstrate that, relative to workers, males of four bumblebee species or species groups (Bombus lapidarius, B. monticola, B. pascuorum, and B. lucorum/magnus/cryptarum/terrestris) tend to congregate at or near the tops of hills. This is, to our knowledge, the first evidence for hilltopping in bumblebees and the first record of any putative mate-locating behaviour for male B. pascuorum, a very common species in Europe. 3. We note that, in common with most previous studies of mate-locating behaviour in bumblebees, attraction of virgin queens and mating were not observed.