It sometimes amazes newcomers to bird watching and birding how some of us old pros can identify birds without the aid of a birding binocular. More than once I have just casually said there is a such and such without even bothering to lift my binocular or even peek through my spotting scope, much to the amazement of the folks in my group. No, this is not bragging; anyone who has been serious birder as long as I have could do the same thing. When you have seen some birds so many thousands of times, you can easily identify them just the way they fly, the way they sit, they way they hop, walk, run and so on, not to mention their general shape and so on. It's often just a combination of these things, rather than a specific clue, but it only comes with experience.
For the same reason, I have noticed a trend among many experienced bird watchers and birders to cut back a bit on binocular size, simply because they don’t need quite so much binocular performance to identify birds, so why carry the extra size and weight? I still recommend a full-size birding binocular for the beginner, since a beginner needs all the performance you can get from a birding binocular, but in truth, there is very little that an 8x42 can do, that an 8x32 of equal quality cannot do.
Okay, you don’t have to watch birds for four decades to learn this art of identifying birds by their general shape and impression; you can do it simply by watching common birds, with or without your binocular, till those birds become so imprinted in your mind that when something new and different shows up, it will stand out like a sore thumb. When that newcomer bird does make an appearance, you will also be surprised at just how subtle some of those clues can be that tell you this bird is different. Next time that flock of House Sparrows invade your bird feeder, take a closer look for that one bird that seems a bit out of place, then take a peek with your binocular. You’ll be an old pro bird watcher in no time.