Selective feeding is when a fish feeds on an organism because of its abundance.
When I was selling flies at the Little Lehigh Fly Shop, I noticed that the flies that sold the best and caught the most fish had two things in common. They’re easy to tie and look the same from all directions.
Real flies don’t tumble; imitations do. Wild trout sense this.
Every fly imitation has four triggering devices: size, silhouette, color, and behavior. A trout notices the primary trigger, usually the silhouette, and approaches the imitation. If nothing is wrong with the secondary triggers the trout will take the imitation. For example, if a trout sees the silhouette of your trico imitation, approaches, and then sees overdressed bulky wings, it will refuse the fly.
The angler needs to evaluate the natural prey and then make sure the fly he buys, or ties captures the primary trigger. The secondary triggering devices should also be present, but I would rather skip the secondary triggers than capture them at the risk of hiding the primary trigger. Selectively feeding trout are looking for what is right not for what’s wrong!
If you’re getting refusals, (assuming your drift and tippet sizes are correct), make adjustments to your fly. Legendary Pennsylvania fly fisherman, Charlie Fox called it “a game of nods”. If a fish would refuse his pattern, he would start trimming down his fly. He would continue to trim his fly until the fish took it. If the fish didn’t take it, he would give it a nod, then be on his way.