First noticed was a Tyrannus flycatcher perched on the top of a Mullen. Initial interpretations were as follows: Much larger and thicker bill than what we thought was normal for a Western Kingbird. It was not vocalizing unlike the other Westerns we had seen previously. I  attempted to document as many features of the bird as possible once we figured it might not be a Western. Wings, tail, bill, breast, back. This bird had yellow stretching from the lower belly all the way to the, yellow/green breast to the pale whitish/gray throat. (Cassin’s and Thick-billed eliminated) As it was hawking for small insects we noticed that the outside edge of the recitrices had no white. The tail feathers were also a dark brown instead of Black. As it landed and faced away from us we saw that the back had at least a little greenish tint not all light gray light a Western. Next we also noticed the tail had a small fork when folded, eliminating Western for sure. Now for the hard ID, Couch’s vs Tropical, these birds are too hard to identify when they are not vocalizing. We played a few calls of both Couch’s and Tropical. The bird seemed totally uninterested with the Couch’s calls but when we played the Tropical it seemed a slight bit agitated. Jason and I waited for about 10 excruciating minutes as we waited for it to call, and sure enough, it eventually did. We learned later that the vocalizations we heard are called by Nathan Pieplow as Chitter calls. At this point, once we obtained decent enough quality recordings to confirm Tropical, we spread the word both on Discord, eBird, and Facebook.