Standing in the lab-kitchen at the nature center, I noticed movement in the distance. A fidgety flutter centered around one tree down slope from the back of the building. It was high in the canopy but because of our elevation difference, it was almost at eye-level.
The hyper little thing was much too far away to see a field marking. I was indoors so couldn't possibly hear a vocalization, but my general impression of the bird was that it was smaller than a chickadee and much more active.
A kinglet? But which one? We have both golden-crowned and ruby-crowned kinglets that spend their winters here in the valley.
Clues to the proper ID are buried in my opening lines. "High in the tree," "centered around one tree" suggest golden-crowned.
What I was practicing was GISS (General Impression of Size and Structure) plus its overall behavior. And kinglets are a good place to start because rarely do you get more than an impression; they're far more ephemeral than in-your-face cardinals.
Most field guides focus on the field markings and vocalizations. They have to because by definition the books are kept small and pocket size. But knowing a species individual behavior is just as important.
That's why I like Pete Dunne's Essential Field Guide Companion. Aptly named, it's meant to be a companion to your field guide and with a good paragraph or two on each bird's behavior for some IDs, it's essential.
Case in point: Golden-crowned kinglet, "forages higher in the canopy [than a ruby-crowned] more site-tenacious forages longer in a tree before moving on...hyperactive feeder, hopping quickly between branches and wing-flicking often...forages by picking or hovering."
It confirm my suspicion, I retrieved my binoculars and when I returned, it was still in the same tree. Yes, a golden-crowned!