title: Vision on the high seas: spatial resolution and optical sensitivity in two procellariiform seabirds with different foraging strategies.
abstract: Procellariiform or 'tubenosed' seabirds are challenged to find prey and orient over seemingly featureless oceans. Previous studies have found that life-history strategy (burrow versus surface nesting) was correlated to foraging strategy. Burrow nesters tended to track prey using dimethyl sulphide (DMS), a compound associated with phytoplankton, whereas surface-nesting species did not. Burrow nesters also tended to be smaller and more cryptic, whereas surface nesters were larger with contrasting plumage coloration. Together these results suggested that differences in life-history strategy might also be linked to differences in visual adaptations. Here, we used Leach's storm petrel, a DMS-responder, and northern fulmar, a non-responder, as model species to test this hypothesis on their sensory ecology. From the retinal ganglion cell density and photoreceptor dimensions, we determined that Leach's storm petrels have six times lower spatial resolution than the northern fulmars. However, the optical sensitivity of rod photoreceptors is similar between species. These results suggest that under similar atmospheric conditions, northern fulmars have six times the detection range for similarly sized objects. Both species have extended visual streaks with a central area of highest spatial resolution, but only the northern fulmar has a central fovea. The prediction that burrow-nesting DMS-responding procellariiforms should differ from non-responding species nesting in the open holds true for spatial resolution, but not for optical sensitivity. This result may reflect the fact that both species rely on olfaction for their nocturnal foraging activity, but northern fulmars might use vision more during daytime.
authors: Lund Vision Group, Department of Biology, Lund University, Sölvegatan 35, Lund 22362, Sweden mindaugas.mitkus@biol.lu.se.
authors: Mindaugas
authors: M
authors: Mitkus
authors: Department of Neurobiology, Physiology and Behavior, College of Biological Sciences, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA.
authors: Gabrielle A
authors: GA
authors: Nevitt
authors: Department of Natural Sciences, University of the Faroe Islands, J. C. Svabos gøta 14, Tórshavn 100, Faroe Islands.
authors: Johannis
authors: J
authors: Danielsen
authors: Lund Vision Group, Department of Biology, Lund University, Sölvegatan 35, Lund 22362, Sweden.
authors: Almut
authors: A
authors: Kelber
mesh_terms: D000818:Animals; D001717:Birds / Q000502:physiology*; D002452:Cell Count; D005247:Feeding Behavior / Q000502:physiology*; D005584:Fovea Centralis / Q000033:anatomy & histology; D009792:Oceans and Seas; D055620:Optical Phenomena; D012165:Retinal Ganglion Cells / Q000166:cytology; D014785:Vision, Ocular / Q000502:physiology*
keywords: Bird visual ecology; Leach's storm petrel; Northern fulmar; Optical sensitivity; Retinal ganglion cell topography; Visual spatial resolution