The Influence of River Flow Rate on the Breeding Behaviour of Calopteryx Damselflies

1. Territorial, courtship and oviposition behaviour of Calopteryx splendens xanthostoma (Charpentier) and C. haemorrhoidalis (Vander Linden) were studied in two freshwater streams in southern France. 2. Females of both species preferred to oviposit in aquatic vegetation found in fast-flowing water. This was not due to preference for a particular species of vegetation; most ovipositions by C. s. xanthostoma occurred in a single species, and female C. haemorrhoidalis ceased ovipositing in an area of fast water after the flow was experimentally slowed. 3. Males of both species defended areas of oviposition vegetation as territories. Territorial disputes were common in fast-flowing parts of the streams while slow-flowing areas were often underfended. Male C. haemorrhoidalis deserted previously defended areas after an experimental decrease in flow rate. 4. The mating success of male C. s. xanthostoma increased with the rate of flow of water through their territory, but only up to a rate of 0.15 m s-1. Above this, males spent so much time in territorial defence that they probably missed mating opportunities. 5. Males of both species sometimes courted females by falling onto the water surface and floating with the current. Males that performed this display had a higher mating success than those that did not. We suggest this display has evolved to indicate territory quality to females.