The present study shows that gentoo penguins possess the ability to recognise and discriminate red and blue colours, which suggests that, despite variations in eye anatomy and habitat compared to other bird species, colour vision maintains an important role in their visual perception.
In penguins the red-light sensitive opsin peak absorbance is shifted to a shorter wavelength respect other avian species. This shift is consistent with the attenuation of wavelength light in ocean water, suggesting that recognising red hues may be useful when hunting. Gentoo penguins possess emmetropic vision both in air and underwater and they mostly hunt nearshore benthic and pelagic, around depths of ~ 20 m, where there is less attenuation of light and corresponds to the diel vertical migration of Antarctic krill (Euphausia superba). This krill made up the majority of prey found in the stomach of these penguins, and it possess carotenoid pigments that confers them a certain hue of red colour, discriminating red from blue could help penguins recognize better the prey and discriminate it from other preys.
Moreover, carotenoid seems to play an important factor for penguins’ health having a part in their immune system and are responsible for their beak colouration, making the krill an important part of their diet. Therefore, individuals with brighter carotenoid-based coloured trait are in better health condition that might indicate also better hunting skills. A strong positive correlation has been found between body mass and red hue in the beak in male gentoo penguins. These findings suggests that this colouration could play a role as a secondary sexual character in males. A manipulative experiment on king penguins (Aptenodytes patagonicus) also suggested a role of coloured patches in sexual selection, however the meaning of these traits is not fully understood in monogamous birds with little to no sexual dimorphism.
Colour vision has been broadly studied in various avian species, underlying its importance in multiple facets of their life, however, it has not been investigated in penguins. To date a lot of information and knowledge about gentoo penguins is still missing, probably due to their ecology and habitat, making it logistically and ethically challenging to study them in the wild, but that also makes them a good indicator species for climate change. Gaining more information on their colour vision may help improve our understanding, for example on the function of their coloured traits. The present study is the first to evaluate colour discrimination behaviourally in penguins. Future studies using a similar research design could evaluate their visual spectrum range and sensitivity both in daylight and dim light. The results of the present study could also be a tool to improve the wellness of captive penguins with the usage of coloured enrichment as well as a training tool.
CONCLUSION
All 14 gentoo penguins included in the study successfully recognized and discriminated red- and blue-coloured targets. Moreover, the very similar correct choice frequency for the three different shades of red and blue confirm that they did, in fact, recognized the colour and not the brightness of the target. The result of males and females did not show any significant difference indicating that colour vision has an important role for both sexes. There was no significant difference neither in the results of individuals trained to touch the red target versus the ones trained to touch the blue target, suggesting that both colours play a role in different aspects of their life. Finally, investigating colour vision in captive penguins can help broaden our knowledge on these animals and improve future studies on their behaviour, as well as ameliorate the wellness of captive individuals.