Interesting concept, just wondering how well it will work and how far down the chain they can take this application? Sony recently announced at Photokina plans for their Eye AF that is currently limited to detecting human eyes, to also detect the eyes of animals. They gave a short demonstration of this working on birds and mammals, but provided no further details on whether or not it would be limited to certain types of animals....No concrete date was given for the support of Animal Eye AF. However it was mentioned that it may be coming in early 2019.... Guess if it works half as good as their current human eye AF technology does, it would be a definite benefit?????

Thousand Oaks the off duty police were not allowed to be armed in the bar, let that sink in.
Police are poorly trained unless they take it upon themselves to train on their own.
I am very proficient and do not wander through life in condition white.
Thousands of lives are saved every year by armed citizens that is not reported because it does not meet the anti gun agenda of fake news.
CCW holders are not shoot happy and are trained regarding shooting and the law. Most attacks are subdued by merely brandishing the firearm as in my case.
Today I believe police due to BLM and obummer trashing them and suing them and criminalizing law enforcement causes police to hesitate when instant action is needed. It is a problem of lack of support for police and their fear of being attacked by the left that causes the split second hesitation and costs them their lives.
This is what I have observed. Yes, I have been in many similar situations in SA as these in the service, I won, no hesitation and didn't miss because I practiced as many scenarios as possible regularly.

The concept is really quite simple.

If you increase the exposure because the background is dark, you risk blowing the highlights on the white feathers. You can't fix blown highlights.

If you reduce the exposure because the background is light, you only get a slightly darker white bird. That's easy to fix.

I took a couple dozen images like this one against different backgrounds using the same manual exposure setting. Some backgrounds were lighter, others darker.

The white birds all came out the same.

The same exposure does not work for the bird in direct sunlight and the one in the shade.

But if a bird in direct sunlight is flying and the background changes from blue sky to dark forest, a reflected reading is likely to increase the exposure and blow out any white feathers. I can't count the number of times I have seen people puzzled by blown out white feathers in situations like this.

What's even more strange is how many times the suggestion is made to spot meter the moving bird. There is entirely too much time wasted here on misinformation like that.

You're right about equivalence... There is no meaning to the use of that phrase here.

However, pixels do not have a physical dimension. They are just numbers representing color brightness values. They can be made larger or smaller when represented by dots of light or ink. That's what the term 'PPI' means. It's an expression of how many pixels will be spread over each inch of output. The very separate term, 'dpi,' is used when talking about scanner samples or printer resolution. How many samples per linear inch am I scanning from a piece of film or a print? How many dots am I using to reproduce each linear inch of output, regardless of the number of pixels spread over that inch? The terms are not really interchangeable.

DOTS do have dimension. When you "enlarge" an image, you are either creating more *pixels* through software interpolation, each of which will be represented by the printer using the same number of dots as if the image were not enlarged, or you are telling a printer driver to use more dots to represent a pixel over a broader area of the paper. Neither process can replace detail, and in fact, both of them slightly reduce detail (interpolation hides the loss a lot better).

There is no substitute for original data. Cropping discards some of what is captured. Enlarging via interpolation in software uses sophisticated algorithms to create fake pixels based upon the original ones, to fill in the "holes" around the real ones when you send the file to the printer for reproduction at a certain size. The idea is to reproduce the pixels with finer granulation (fewer dots per pixel), to make their edges smoother and less visible.

They were, yes, with a 2x behind a 500mm prime. The experiments I've observed with a 70-200 f/2.8L is that doubling this lens can be as good as the 100-400 for image quality. But, those experiments tend to be images of lines are charts and don't include tracking birds in flight. The 100-400L II provides the option of extending out to 560mm on an ever growing number of EOS bodies. I have a stream of posts now prepared of real-world results with various extenders and lenses. Stay tuned at a UHH near you

For our OP, before buying, you should address the earlier question and comments about using an EF 70-200 F/2.8 IS II (or now available III). If you have a version that is a good candidate, try renting both the 1.4x and 2x and make a hands-on experiment and analyze the resulting images to determine how best to address your need.