Hi! Thanks for replying! Very cool story about the Ruby-crowned Kinglet! Bird calls can be pretty tricky...one of the ways that helps to remember bird calls is to split each call into smaller parts and break them apart into different characteristics. Some examples of this is to separate a call based on different pitch, trills, or rhythm. Sometimes, although it might be a little strange, I'll repeat the calls to myself to engrave it in my permanent memory. :) In addition, even looking at spectrograms benefits your ability to identify calls! A lot of birds have repeating segments, and by remembering what the phrase is and knowing how many times it's repeated can definitely help with differentiating different calls. The Northern Cardinal repeats the beginning of the downward slur several times, and its song is usually fairly clear and crisp. Some birds may have a raspier song, or possibly a smooth and "laser-like" voice. The way that each bird's voice sounds, much like humans will probably be different! When people see an image along with audio, this will help commit both the images and sound to memory and will associate one with the other. I may suggest taking note of the pitch and duration of the notes. It's impressive how you identified the Ruby-crowned Kinglet! Moreover, one of the most important factors to take in is practicing and time. Taking just a couple of minutes to focus on bird calls or songs can, over time, help drastically with song identification. These are just a couple of suggestions--many other techniques may work fantastic for you and others, and I suggest you continue doing what helps you. :) I really hope this helps! Have a wonderful day.