Territorial behaviour associated with feeding in both sexes of the tropical zygopteran, Libellago hyalina (Odonata: Chlorocyphidae)

Abstract

Territorial behaviour associated with adult odonate feeding in a Bornean rain forest under-storey is described and its underlying causes are analysed. Immature males and females of all ages of Libellago hyalina defended perches along a narrow trail in kerangas forest, concentrating especially around patches of sunlight. Throughout the day there was displacement of individuals as the illuminated areas moved and population levels of foragers increased, with maximal density from 13:00 – 15:00 h, but territorial success which followed physical combat could not be associated with size, sex or age. Foraging rates were also highest in this period but peaked clearly at 14:00 h. Both foraging attack rates and attack success were higher in sun patches than in shaded territories. Potential prey, mostly small Diptera < 4 mm length, were more abundant along the trail than in the surrounding forest, but were not concentrated in sunlight. It is suggested that, against the dark backdrop of the forest under-storey, prey became much more visible in sunlight, and were more easily detected and more easily captured, hence sites near sun patches were strongly contested. This behaviour constitutes a hitherto undescribed foraging strategy, which may be characterized as follows: “increasing capture success by concentrating in situations where prey visibility is enhanced by overhead sunlight against a dark background.” It is suggested this strategy may be common in tropical rain forest, home to a majority of Odonata species.

Keywords: Odonata, dragonfly, Borneo, rain forest, feeding territory, foraging strategy, sunspots, Chlorocyphidae

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