Supplementary Material for: Development of the Visual System in a Burrow-Nesting Seabird: Leach's Storm Petrel

<p>Little is known about the development of vision in wild birds. It is unknown, for example, whether the ability to see can be predicted by the level of prenatal growth or whether the eyes are open at hatching in a particular species. In this study, we investigated the growth of eyes, the formation of retinal ganglion cell topography, and the appearance of simple, visually guided behaviours in chicks of a small procellariiform seabird, Leach's storm petrel (<i>Oceanodroma leucorhoa</i>). This semi-precocial species, which has a well-developed sense of smell, nests in underground burrows where adults provision chicks for 6-8 weeks in the dark before fledging. Retinal ganglion cell topographic maps revealed that fine-tuning of cell distribution does not happen early in development, but rather that the ganglion cell layer continues to mature throughout provisioning and probably even after fledging. While the olfactory bulbs reached adult size around 7 weeks after hatching, the eyes and telencephalon continued to grow. Optokinetic head response and artificial burrow finding experiments indicated that chicks in the 2nd week after hatching lack even the most basic visually guided behaviours and are probably blind. Thus, vision in Leach's storm petrel chicks starts to function sometime around the 3rd week after hatching, well after the eyes have opened and the olfactory system is functional.</p

Hydrodynamic aspects of fish olfaction

Flow into and around the olfactory chamber of a fish determines how odorant from the fish's immediate environment is transported to the sensory surface (olfactory epithelium) lining the chamber. Diffusion times in water are long, even over comparatively short distances (millimetres). Therefore, transport from the external environment to the olfactory epithelium must be controlled by processes that rely on convection (i.e. the bulk flow of fluid). These include the beating of cilia lining the olfactory chamber and the relatively inexpensive pumping action of accessory sacs. Flow through the chamber may also be induced by an external flow. Flow over the olfactory epithelium appears to be laminar. Odorant transfer to the olfactory epithelium may be facilitated in several ways: if the olfactory organs are mounted on stalks that penetrate the boundary layer; by the steep velocity gradients generated by beating cilia; by devices that deflect flow into the olfactory chamber; by parallel arrays of olfactory lamellae; by mechanical agitation of the chamber (or olfactory stalks); and by vortices. Overall, however, our knowledge of the hydrodynamics of fish olfaction is far from complete. Several areas of future research are outlined