BILL MORPHOLOGY OF IBISES SUGGESTS A REMOTE-TACTILE SENSORY SYSTEM FOR PREY DETECTION

Birds that forage by probing must often use senses other than vision to find their prey. Remote touch is a sense based on the interception of vibrations produced by moving prey in the substrate or on the evaluation of pressure patterns produced by hard-shelled sessile prey. In probing birds, this system is mediated by an organ made up of clusters of mechanoreceptors housed within pits in the bone of the bill-tips. This bill-tip organ was first described in probing shorebirds (Scolopacidae), and more recently in kiwi (Apterygidae). Here, we describe this bill-tip organ in a third family of probing birds, the ibises (Threskiornithidae). We examined the bill morphology of 11 species of ibis from 8 genera. We found bill-tip organs in species in a wide range of habitat types, from predominantly terrestrial to predominantly aquatic, which suggests that ibises may use remote touch when foraging both in water and in granular substrates. Our data imply a link between bill-tip morphology and habitat use a pattern that we believe warrants further investigation. Received 10 March 2009, accepted 17 September 2009.