When a pest-control species becomes a pest: A shift in the foraging habitat of cattle egret (Bubulcus ibis) and the threat to grazed natural ecosystems

Ecosystem services such as natural pest control and pollination may benefit agriculture, but may also adversely affect adjacent ecosystems. Here, we explored the cosmopolitan cattle egret (Bubulcus ibis), a commensal insectivorous large bird which has been expanding worldwide and is often considered as a pest control agent. We assessed the changes in the distribution of this new resident and its nesting and foraging habitat preferences in Mediterranean agroecosystems in northern Israel over the last few decades. We evaluated the relative importance of reptile, amphibian and arthropod prey in its diet by analysing regurgitated food in nesting colonies, and modelled the effect of land-use on reptile prey composition. We found that a recent expansion of B. ibis has been facilitated by the introduction of cattle grazing to natural habitats, and by augmentation of human-dominated landscapes and crop fields. Arthropods have dominated the egret diet (73.75 %), but the overwhelming proportion of reptile species (19.67 %) comprises predominantly maquis dwellers, indicating high predation pressure in natural rangelands. Although B. ibis acts as an agricultural pest control agent in croplands, its function as a harmful predator in grazed natural habitats seems to be substantial. Such intrusion of a novel predator into natural ecosystems may have catastrophic implications for native fauna, particularly in human-dominated and fragmented landscapes. Our findings underscore the potential adverse effects of a naturally thriving predator on local fauna and the importance of further research to understand its actual impact on both agricultural pests and non-pest prey communities in the wild.