The dawn flight of the gold swiftHepialus hecta: predator avoidance and the integration of complex lek behaviour (Lepidoptera, Hepialidae)

Abstract

Predator pressure is a considerable evolutionary force. The evening twilight flight of species in the family Hepialidae Swift moths has been attributed to the moths (which have no hearing and so cannot detect bats) flying in a bat/bird free window. Several species deploy elaborate lek behaviour in this period. The expected flight in the dawn twilight is little reported, except in the non-leking Hepialus (Korscheltellus) gracilis. A detailed study of the dawn flight in the leking species Hepialus (Phymatopus) hecta shows that it is less extensive than the evening lek flight (both in duration and in the number of moths participating), is confined to a much narrower window around sunrise, involves no reproductive behaviour, and functions only to re-locate the members of copulating pairs and sessile displaying males from the emergent ground vegetation to less conspicuous roosting sites. Compilation of individual biographies over the 24-h cycle permits a full construction of the diel activity in time and space. It consists of two twilight flight periods, separated by prolonged roosting during the hours of darkness and daylight. The moths use almost the whole available range of roosting sites, from the base of the ground vegetation to the tree canopy, and cyclically leave and re-enter the lek site from these positions. The copulating posture and position avoid mammalian predators, and facilitate escape from spiders and wasps by the efficient use of a dead drop. The narrowness of the dawn flight is attributed to the need for this prolonged but conspicuous copulation, which precludes a morning mating, and to a demonstrated asymmetry of twilight activity in birds. The whole integrated spatio-temporal cycle is attributable to evolutionary pressure to minimize the impact of predators, demonstrated to include birds, bats, wasps, and spiders, and probably also dragonflies, mice and shrews; the pre-existing dawn flight is permissive to the evolution of sessile male displays during the evening lek. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110, 305–319.