title: Ultraviolet sensitivity and colour vision in raptor foraging.
abstract: Raptors have excellent vision, yet it is unclear how they use colour information. It has been suggested that raptors use ultraviolet (UV) reflections from vole urine to find good hunting grounds. In contrast, UV plumage colours in songbirds such as blue tits are assumed to be 'hidden' communication signals, inconspicuous to raptors. This ambiguity results from a lack of knowledge about raptor ocular media transmittance, which sets the limit for UV sensitivity. We measured ocular media transmittance in common buzzards (Buteo buteo), sparrowhawks (Accipiter nisus), red kites (Milvus milvus) and kestrels (Falco tinnunculus) so that, for the first time, raptor UV sensitivity can be fully described. With this information, and new measurements of vole urine reflectance, we show that (i) vole urine is unlikely to provide a reliable visual signal to hunting raptors and (ii) blue tit plumage colours are more contrasting to blue tits than to sparrowhawks because of UV reflectance. However, as the difference between blue tit and sparrowhawk vision is subtle, we suggest that behavioural data are needed to fully resolve this issue. UV cues are of little or no importance to raptors in both vole and songbird interactions and the role of colour vision in raptor foraging remains unclear.
authors.affiliation: Department of Biology, Lund University, Sölvegatan 35, 22362 Lund, Sweden. olle.lind@biol.lu.se
authors.forename: Olle
authors.initials: O
authors.lastname: Lind
authors.forename: Mindaugas
authors.initials: M
authors.lastname: Mitkus
authors.forename: Peter
authors.initials: P
authors.lastname: Olsson
authors.forename: Almut
authors.initials: A
authors.lastname: Kelber
mesh_terms: D000042:Absorption; D000818:Animals; D003411:Arvicolinae / Q000652:urine; D055253:Color Vision / Q000528:radiation effects*; D015350:Contrast Sensitivity / Q000528:radiation effects; D005241:Feathers / Q000528:radiation effects; D005247:Feeding Behavior / Q000528:radiation effects*; D008297:Male; D010858:Pigmentation / Q000502:physiology; D011235:Predatory Behavior / Q000528:radiation effects; D020304:Raptors / Q000502:physiology*; D012168:Retinal Pigments / Q000378:metabolism; D014466:Ultraviolet Rays; D014828:Vocalization, Animal / Q000502:physiology
chemical_list: D012168:Retinal Pigments
keywords: bird vision; ocular media transmittance; raptor hunting behaviour; ultraviolet reflectance; visual modelling; vole urine