Comparative foraging behaviour of three heron species in small standing-water ecosystems in the arid zone of Oman

Abstract

The composition of assemblages, diet and behaviour of waterbird species with similar ecological features are important aspects in the functioning of aquatic ecosystems. Closely-related animal species often share resources such as space and food in ways that reduce competition, but if the diets of different species strongly overlap, interspecific competition may intensify. This analysis examined behavioural data relating to Great Egret, Little Egret and Squacco Heron in order to explore their foraging efficiencies in rich aquatic habitats in an arid zone during post-breeding movements. The fieldwork was carried out in small estuaries of a wadi on the southern coast of Oman. The frequency of interactions was the highest in Squacco Heron and the lowest in Great Egret. However, the differences in the numbers of inter- and intraspecific interactions between the three species were significant. Activity indices calculated for a five-minute period, i.e. the number of interactions (interaction index) and times of flying and walking (movement index) differed among the three species. The number of successful attacks was the highest in Squacco Heron, while the foraging effectiveness of Great Egret and Little Egret was similar. GLM analysis showed that only the movement index was significant, as it had a positive impact on individual foraging success. Great Egret caught more fish than the other two heron species which, in turn, caught a greater number of smaller prey items, mostly invertebrates. This study shows that heron species in the same rich habitat employ different foraging tactics. In comparison to the other two heron species, the foraging tactics of Squacco Heron seem to be the most susceptible to competition. However, its greater mobility and using different foraging tactics, enhance its foraging success.