Dynamic duos are some of my favorite bird photos. It’s the smallest group of birds possible, which makes composition more manageable. The pair can be together, evoking a couple (and sometimes they probably are a pair, or a parent and child). They can also be separated to fill out the frame. As a photographer, you get many of the benefits of multiple birds without the hassle of having too many.
While duos can be dynamic, three is often the magic number. With three you can make a “V” or a triangle (which are actually the same thing). Odd numbers, especially prime numbers, can often feel more random to us because, I don’t know, math or psychology or something. At any rate, trios, or trilogies, as the French like to call them, are a great for creating both movement and balance in a composition.
And, of course, having two or three of the same species can be very nice because it allows you to focus on the positioning without being distracted by differences in the building blocks. But, mixing up your birds gets you a very different, but also very nice result.