The Bird That Sings C, Bb, G

There’s a bird in our yard these days, and it sings a high descending C, Bb, G, holding the first note longer than the other two, and sometimes repeating the last note several times. Are any readers who are also birdwatchers able to offer some suggestions as to what it might be? I’m starting to think maybe it is just a catbird repeating something it heard somewhere. I still have not managed to spot which bird is singing this.

Thanks for your help! I promise I’ll ask or talk about something else more typical of this blog later…