Visual abilities in two raptors with different ecology.
Differences in visual capabilities are known to reflect differences in foraging behaviour even among closely related species. Among birds, the foraging of diurnal raptors is assumed to be guided mainly by vision but their foraging tactics include both scavenging upon immobile prey and the aerial pursuit of highly mobile prey. We studied how visual capabilities differ between two diurnal raptor species of similar size: Harris's hawks, Parabuteo unicinctus, which take mobile prey, and black kites, Milvus migrans, which are primarily carrion eaters. We measured visual acuity, foveal characteristics and visual fields in both species. Visual acuity was determined using a behavioural training technique; foveal characteristics were determined using ultra-high resolution spectral-domain optical coherence tomography (OCT); and visual field parameters were determined using an ophthalmoscopic reflex technique. We found that these two raptors differ in their visual capacities. Harris's hawks have a visual acuity slightly higher than that of black kites. Among the five Harris's hawks tested, individuals with higher estimated visual acuity made more horizontal head movements before making a decision. This may reflect an increase in the use of monocular vision. Harris's hawks have two foveas (one central and one temporal), while black kites have only one central fovea and a temporal area. Black kites have a wider visual field than Harris's hawks. This may facilitate the detection of conspecifics when they are scavenging. These differences in the visual capabilities of these two raptors may reflect differences in the perceptual demands of their foraging behaviours.
Department of Evolutionary Ecology and Department of Biodiversity and Conservation - CEFE UMR 5175, CNRS-Université de Montpellier-Université Paul-Valéry Montpellier-EPHE, 1919 route de Mende, 34293 Montpellier, Cedex 5, France simon.POTIER@cefe.cnrs.fr.
Simon
0000-0003-3156-7846
S
Potier
Department of Evolutionary Ecology and Department of Biodiversity and Conservation - CEFE UMR 5175, CNRS-Université de Montpellier-Université Paul-Valéry Montpellier-EPHE, 1919 route de Mende, 34293 Montpellier, Cedex 5, France.
Francesco
F
Bonadonna
Department of Biology, Lund University, Sölvegatan 35, Lund S-22362, Sweden.
Almut
A
Kelber
School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
Graham R
GR
Martin
Centre Hospitalier Vétérinaire, Unité d'Ophtalmologie, 275 route Impériale, Saint-Martin Bellevue 74370, France.
Pierre-François
PF
Isard
Centre Hospitalier Vétérinaire, Unité d'Ophtalmologie, 275 route Impériale, Saint-Martin Bellevue 74370, France.
Thomas
T
Dulaurent
Department of Evolutionary Ecology and Department of Biodiversity and Conservation - CEFE UMR 5175, CNRS-Université de Montpellier-Université Paul-Valéry Montpellier-EPHE, 1919 route de Mende, 34293 Montpellier, Cedex 5, France.
Olivier
O
Duriez
D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D017753:Ecosystem; D005260:Female; D005584:Fovea Centralis; D008297:Male; D020304:Raptors / Q000502:physiology*; D015348:Vision, Binocular; D014785:Vision, Ocular / Q000502:physiology*; D014792:Visual Acuity / Q000502:physiology; D014794:Visual Fields / Q000502:physiology
Black kite; Fovea; Harris's hawk; Raptor vision; Visual acuity; Visual field