Post-hatching development of the remote-tactile bill-tip organ in precocial shorebirds (Scolopacidae)

Several groups of birds that rely on tactile foraging methods to locate prey exhibit specialized bill-tip organs to sense tactile cues. Most scolopacid shorebirds (sandpipers and kin) employ the sensory capability of remote-touch during foraging, allowing them to locate buried prey at a distance from their bills by detecting vibrational cues in the substrates they probe in. This is facilitated by a bill-tip organ made up of dense clusters of mechanoreceptors housed within a constellation of neurovascular foramina in the bone at the tips of their bills. Bill-tip organ morphology has been shown to correlate with foraging ecology; however, all previous research has focused on adult birds. Many tactile foraging birds, including scolopacids, have precocial young that forage independently within hours of hatching, yet remote-touch foraging and its morphological correlates in juvenile birds remain unexplored. Here, we use μCT scans to describe the morphology of the bill tips of juvenile-adult pairs of several scolopacid species to characterize the post-hatching development of the bill-tip organ. We show that the osteological correlates of functional bill-tip organs are present in juvenile scolopacids and describe changes in bill-tip organ morphology during post-hatching development. Our results suggest that juvenile scolopacids, and likely other precocial tactile foraging birds, are able to sense tactile cues with their bills from the point of hatching. Our data additionally suggest that previously described interspecific variation in bill-tip organ morphology associated with taxon-specific foraging behaviours and habitat preferences appears to develop after fledging and dispersal in scolopacids. These data reveal ontogenetic and interspecific differences in scolopacid bill-tip organ morphology associated with differing ecologies and improve our understanding of foraging behaviour of juvenile shorebirds.