Ultraviolet vision in birds: the importance of transparent eye media

Abstract

Ultraviolet (UV)-sensitive visual pigments are widespread in the animal kingdom but many animals, for example primates, block UV light from reaching their retina by pigmented lenses. Birds have UV-sensitive (UVS) visual pigments with sensitivity maxima around 360–373 nm (UVS) or 402–426 nm (violet-sensitive, VS). We describe how these pigments are matched by the ocular media transmittance in 38 bird species. Birds with UVS pigments have ocular media that transmit more UV light (wavelength of 50% transmittance, λT0.5, 323 nm) than birds with VS pigments (λT0.5, 358 nm). Yet, visual models predict that colour discrimination in bright light is mostly dependent on the visual pigment (UVS or VS) and little on the ocular media. We hypothesize that the precise spectral tuning of the ocular media is mostly relevant for detecting weak UV signals, e.g. in dim hollow-nests of passerines and parrots. The correlation between eye size and UV transparency of the ocular media suggests little or no lens pigmentation. Therefore, only small birds gain the full advantage from shifting pigment sensitivity from VS to UVS. On the other hand, some birds with VS pigments have unexpectedly low UV transmission of the ocular media, probably because of UV blocking lens pigmentation.

Visual pigments in a palaeognath bird, the emuDromaius novaehollandiae: implications for spectral sensitivity and the origin of ultraviolet vision

“…Based on the two-term exponential relationship between l T0.5 and log 10 axial length (mm) [53], the predicted l T0.5 for the emu eyes measured in this study (eye axial lengths 32-34 mm) would be approximately 360 nm, which is consistent with the measured value of 355 nm. Both emu and ostrich have l T0.5 values that are characteristic of bird species that possess VS (mean l T0.5 ¼ 358 + 20 nm) rather than UVS SWS1 pigments (mean l T0.5 ¼ 323 + 10 nm) [53]. Thus, neither eye size nor ocular media l T0.5 are totally reliable predictors of the SWS1 l max value, although there remains a general relationship that warrants further investigation.…”

Boreal bird abundance estimates within different energy sector disturbances vary with point count radius

“…Recent research suggests that avoidance by reindeer (Rangifer tarandus) may be linked to their ability to detect ultraviolet (UV) light emitted by transmission lines (Tyler et al 2014). At least some birds also see in the UV spectrum (Lind et al 2014), but the potential implications of this for indirect effects have not been thoroughly investigated.…”

Dim ultraviolet light as a means of deterring activity by the Hawaiian hoary bat Lasiurus cinereus semotus

“…Although some nocturnal birds, such as owls and species in the family Caprimulgidae (e.g. nighthawks, nightjars and poorwills) have eyes approaching or equaling the light sensitivity of bats, there are no known cases of nocturnal birds that possess extreme low-light sensitivity at UV wavelengths (Ödeen & Håstad 2003, Martin et al 2004, Lind et al 2014. We have little reason to believe that nocturnal birds would be attracted to dim UV illumination.…”