Ethel Merman. Singing one call over and over isn't anything I've noticed one doing before. I sketched it, just in case I was wrong, and as I finished drawing, the mockingbird began to sound like a mockingbird. You can see in the sketch that both birds were quite puffed up. It was cold and the sun was just beginning to warm things up. Mockingbirds eat insects, which were probably waiting for some warmth before starting to buzz about, so I think it was as if that mocking bird just hadn't had that first cup of coffee yet.
Oh, when I got home later and looked up Bullock's oriole (Icterus bullockii), I was surprised to find that I'd most likely seen a Hooded oriole (Icterus cucullatus) instead. Both occur in my area but the Bullock's is more common and that's what I was expecting to see. I was pleased that my drawing helped me sort out the difference!