Shivering and its cost during reproductive behaviour in Neotropical owl butterflies, Caligo and Opsiphanes (Nymphalidae: Brassolinae)

Abstract. Male owl butterflies Caligo and Opsiphanes were gathered during crepuscular hours along an edge habitat, where they engaged either other males of the same species in aerial encounters, or females in courtship and copulation. Shivering elevated thoracic temperature during crepuscular hours approximately 10°C above ambient temperature for Caligo and 15°C for Opsiphanes in phase with reproductive activities for both males and females. Male displays endured on average 30 min, and the estimated cost of maintaining an elevated body temperature during this time was 3 mg of fat for each bout. Owl butterflies are generally lethargic during daylight hours and rarely shivered and never basked in sunlight during these times. Owl butterflies shivered in ambient temperatures (24-26°C) that were well above the lower critical temperature for flight (19-20°C). Shivering did not elevate abdominal temperature, and hence the butterflies did not raise their temperature to make pheromones volatile from abdominal scent glands. By elimination of these alternative hypotheses, it was concluded that shivering to elevate thoracic temperature prepares owl butterflies for reproductive encounters.