What is this nearly closed, foggy curtain?

 A crow had just touched down on a rock around the pond and took one step towards the water. Then I found a foggy curtain sliding in the crow's eye.

I felt I was having an optical illusion.

It looked like a membrane slid over its pupil. It looked like sliding horizontally from the corner of it's eye. It wasn't lucky that I only saw it once. 

So I was able to take one photo, but no video. If I had the chance again, I would like to make a video of the closing movement, but it may be impossible. 

Intrigued, I looked into the matter. I am not an ornithologist. Wildlife readings on crow's eye, readings on animals for teenagers, authoritative literature and Twitter I did a web search. A search of Twitter also found some academic tweeting photos of nictitating membranes. And I found it. 

It is the protective shield without closing the eyelids. It is called the nictitating membrane. Nictitating membranes are present in birds, reptiles, amphibians, fish and even some mammals. Having said that, I have also learnt the word nictitate. It means the same as wink or blink. I have saw the moment their eyes nictitated.

Yes I was convinced that it was the fact. It looked to me as if it had slid horizontally too. 

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The crows' feathers must be deep navy blues

Do crows have black feathers?

Take a look at this photo of a crow I took at the Former Yasuda Garden. How do they look to you?

The crows' feathers must be deep navy blues with some purple tints.

I am not an ornithologist or a birdwatcher.

I just enjoy walking in the garden and taking photos of flowers, ducks and herons.

What I have seen recently is that crow feathers are not black. 

Unfortunately, the crow also appeared to have an injury to its feathers.

I think crows are often described as black birds only because they seem to prefer dark places. I photographed a crow when it landed on the edge of the garden pond and basked in the sunlight. Just then, I feel, the crow's feathers reflected the light and shone, showing their true colours. 

There are deep navy blues with some purple tints to it.

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