As tools for bird identification goes, using a bird's
size is a sometimes thing. Just noting that a lone bird is small, medium, large and then using it to identify a bird is almost worthless, since an individual bird's apparent size can appear to change, greatly, under various conditions of lighting, distance, plumage and so on. I was burned more than once on using size on a lone bird as a
birding identification tool in my early years. Okay, so when is size a useful birding tool? A bird's size is actually an excellent way to identify a bird when it is in close proximity to another bird species that you have identified and can use as a comparison. A good example of this works for me is at my local marsh. In this little honey hole there are hordes of Killdeer running up and down the shore. Check you bird guide and you will note that an adult Killdeer is a 10 1/2" bird. It then becomes relatively easy to gauge the size of that sandpiper standing next to it. If it appears to be much smaller, good chance you have a peep. If it is not quite as large, maybe a Baird's and so on. This becomes second nature after awhile. Last week, I had Solitary Sandpipers, Baird's Sandpipers, Semipalmated Sandpipers and even a Greater Yellowlegs, all in close proximity to my helpful Killdeers and all of them visible at times in the field of view of my
Leica 10x25BL. That makes it even more fun and it is a real kick to see the way the sizes listed in the bird guides for all these birds matched up with what I was seeing in the binocular.