Sony has, imo, a remarkable exposure method that helps make the issue of proper exposure for whites a non-issue. The technology is referred to a "zebras". When set up properly, zebras will show up on over exposed portions of your frame and can be controlled by whatever parameter you choose (aperture, shutter speed, or ISO). With birds or other action subjects when you need to react quickly, I find adjusting ISO to be the easiest method. It's my understanding that this is not the same as blinks, in other systems. Tell me if I am wrong; blinkys are applied to the
JPEG image you are looking at in your camera and can misrepresent the proper exposure of a raw file which has greater dynamic range. Using zebras requires a bit of calibration for the camera you are using, but once set up properly, can provide a method of controlling highlights in whatever situation you are encountering, not just white birds. Other manufactures may also provide this exposure control method but I am not familiar with them. Good luck.

Given that you are shooting in bright sunlight, in general use matrix metering or evaluative metering and then set some level of negative exposure compensation. The amount set can vary with the camera body and light conditions. The key is to see detail in the whites of feathers and avoid feathers or birds that look too "grey". My starting amount might be a -.7 or maybe a -1.0. I am rarely at anything greater than -1.7.

If you are using a mirrorless camera the effects of the exp comp settings should be present in the viewfinder before you take the image. Being able to preview the impact of such changes is a major benefit of suing a mirrorless camera.

You can meter anyway you want, but Canon's evaluative metering is the easiest and the most receptive to the ideas above regarding EC and the relative + / - position of the meter vs the 0-mark.

To the idea of ETTR - Exposing to the Right and capturing in RAW, as long as you don't 'blow' the highlights, you can use a combination of your Highlights slider and your Whites slider in post to bring out the RAW details (lower highlights) and maintain the original whites of the bird (increased whites). This post includes a working example:

ETTR in Practice II

Do you want white birds, or grey birds? Do you want a grainy underexposed sky to go with those grey birds?

You should capture in RAW with the exposure settings that stop just 1/3-stop below causing exposure highlights on the birds. Of course, that's going to take some experimentation in the actual light and subjects to confirm, work you should be planning to execute in all situations.

Leverage the modern marvel that is the EOS R7 that enables manual exposure with Exposure Compensation and AUTO ISO. Just pick your shutterspeed and aperture in M, then adjust the EC dial as you experiment with the birds and the exact light. Let the EC level and reviews of the highlight warnings determine exactly the + / - offset position of the meter.