If you take optics outside, you will eventually be confronted by an environment in which raindrops gather on your ocular lenses. But “confronted,” is not the same as “confounded.”
Yes, you’ll have raindrops on the lenses. No big deal. Most optics are sealed well enough to shrug off moisture. Most people’s first instinct is to wipe the lens. This is fine, providing you have the time and a proper lens-cleaning cloth. A quick swipe or a wipe with an ineffective, non-absorbent material (such as wool or synthetic pile), will only make the situation worse, smearing the lens with an opaque film. My advice for when time is short and a quick look at a bird is all you get is to simply look through the raindrop-spattered lenses. Yes, the image will be pocked with dark spots, but you will still see the bird.
Note, too, that some premium binoculars come with a water-shedding coating on the lenses. A rapid shake is all you need to send droplets flying.
Keeping your neck strap short will allow your chin and hat brim to prevent droplets from gathering at all. Rain guards, are, of course, ideal protection, providing they don’t fit so snugly that the resulting vacuum/suction prevents easy removal. I’ve seen some rain guards so tight their removal pulled the ocular lens right out of the instrument.
You can make your own rain guard out of a square of chamois cloth cut with slits to accommodate your binocular strap. The cloth then folds over the oculars. It’s simple, cheap, and effective.