Diet of Cattle Egrets ( Bubulcus ibis ibis ) in the Flood Valley of the Paraná River,Northern Argentina

Abstract

We analysed the feeding ecology of Cattle Egrets (Bubulcus ibis ibis) based on 30 individuals captured on the Carabajal island, Santa Fe, Argentina (31°39′S, 60°42′W), determining the minimum sample, index of relative importance (IRI), size of prey, feeding efficiency, dietary selectivity, amplitude of the trophic niche, standardisation, circadian rhythm of feeding activity and habitat preference. The trophic spectrum was made up of 17 taxonomic entities, mainly insects (IRI = 15,000), among which orthopterans were the most numerous followed by spiders and amphibians (IRI = 250). The highest percentage of prey size was found in the interval 21-30 mm. The amplitude of the trophic niche ranged between 1.98 and 3.45, and the feeding efficiency between 89 and 92%. In relation to dietary selectivity, the correlation between abundance of prey in stomachs and abundance of prey in the study area yielded no significant results (r_s = 0.84, P.0:001). The rhythm of feeding activity responded to the bell-shaped model, which meant a peak in its feeding behaviour pattern at the noon hours. The pastures were the units of vegetation and environment selected more frequently.