Diel pattern of activity, mating, and flight behaviour in Onychogomphus uncatus (Odonata: Gomphidae)


The behaviour of Onychogomphus uncatus, including flight and mating activity, was studied at a fast-flowing irrigation canal. During the day, males perched in sections of the canal with a strong current and a turbulent water surface. During short flights, interactions with other con-specific and hetero-specific males occurred, particularly with Orthetrum coerulescens. Under conditions of high population density, the frequent occurrence and disturbances by this species often resulted in male O. uncatus leaving a particular section of the canal. In the late afternoon and evening, males concentrated on ground perches in the vicinity of the water. The reproductive system of O. uncatus was found to be ‘encounter limited’. The operational sex ratio of imagines at the water was always strongly biased in favour of the males. Individual females were observed at the water during the morning and evening hours. Following pair formation there was a prolonged period of copulation away from the water. Most pair formations were observed in the morning and evening hours. They took place over water, and in the evening hours also away from the water.

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