Dietary overlap between the nocturnal letter-winged kite 'Elanus scriptus' and barn owl 'Tyto alba' during a rodent outbreak in arid Australia

Abstract

The letter-winged kite 'Elanus scriptus' is unique in being the only truly nocturnal raptor (Falconiformes). An endemic of arid/semi-arid Australia, the kite is sympatric with the barn owl, 'Tyto alba', throughout most of its range. Although the letter-winged kite is nocturnal, it seems to possess intermediate degrees of adaptation for nocturnal hunting, whereas the barn owl is specialized for nocturnal activity. We studied sympatric populations of both species during a rodent population outbreak in the north-west Simpson Desert to understand how their different nocturnal adaptations influenced diet and prey selection. The commonest rodents, in order of abundance, were 'Pseudomys australis' (body mass: 40–75 g), 'P. hermannsburgensis' (9–17 g), and 'Notomys alexis' (27–45 g). Rodents dominated the diets of kites (96% of 225 prey items) and owls (98% of 303 prey items). Dietary niche breadth was relatively low for both kites (BA=0.16) and owls (BA=0.13), whereas niche overlap was extremely high (O=0.98). Barn owls exhibited greater prey choice, specifically; they selected the larger 'P. australis' and avoided the small 'P. hermannsburgensis', whereas kites captured 'Pseudomys' species in proportion to their availability.