Remote touch prey-detection by Madagascar crested ibises Lophotibis cristata urschi

Birds that forage by probing must often rely on sensory systems other than vision to detect their buried prey. Such senses may include hearing (e.g. Australian magpies (Atramidae), American robins (Turdidae)) or chemical senses/olfaction (e.g. kiwi (Apterygidae) and some shorebirds (Scolopacidae)). Probe foraging kiwi and shorebirds are also able to use vibrotactile cues to locate prey buried in the substrate at some distance from their bill-tips ('remote touch'). These birds possess an organ consisting of a honey-comb of sensory pits in bone of the bill-tips, packed with mechanoreceptive nerve ending (Herbst corpuscles). Such a bill-tip organ has recently also been described in ibises (Threskiornithinae), but its function not elucidated. We designed a foraging experiment presenting mealworm prey to three captive Madagascar crested ibises Lophotibis cristata urschi under a variety of trial conditions to discover whether they were using remote touch, mediated by their bill-tip organ; chemosense/olfaction; or hearing to locate buried prey. The ibises were reliant on remote touch for prey detection - the first time this sensory system has been demonstrated for this group of birds. They did not appear to use hearing or chemical senses/olfaction to aid in prey detection.