Why do "Great" Birds have yellow eyes?

Thought I keep today's post nice and short - mainly because not much wildlife was observed today.

View of Terra Nova Slough

Nevertheless, some questions popped into my head when I am looking through the photos on the computer - why do different bird species have different eye colors, and what role does it play (in predating)?

Great Horned Owl (Bubo virginianus)
Great Horned Owl - big, round, yellow eyes.

Great Blue Heron (Ardea herodias)
Another "Great". Great Blue Heron - small(er), round, yellow eyes.

I couldn't find any scientific explanation about why top predators like most owls and raptors all have yellow/orange/reddish eyes. But Ecobirder posted some interesting facts about the eyes of raptors on his earlier post.
- Raptors have excellent distance vision and outstanding visual acuity (due to the thicker retina).
A raptor's eyes can make up to 15% (or higher) of their body.
- Large eyes mean not much room for eye muscle attachment in the socket (and less room in the skull for brain), so the eyes are fixed in place (therefore, they need to turn their heads to see).

Personally, I think having yellow eyes make you look more threatening and intimidating, which works well if you are a ferocious predator.


Chris said...

It might also be something linked to accumulation of light and intensity! I do no know really, but what I know is that these shots of yours are marvelous and sharp on the eyes of the birds. Great pictures.

Tarolino said...

Interesting observation. Must be something to do with seeing in the dark too as cats (big and small) have mostly yellow eyes and they have excellent night vision.

PSYL said...

Thanks for the hypotheses! I wonder...

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