I agree that these are one of the cutest birds. With their (apparently) huge black eyes these tiny birds look like something drawn for a Disney movie.
Although they were abundant in Southern Texas last winter, it was very difficult to get the camera on them because they are so very active. I've never seen one sit still for more than a second or two. Attached is the best pic I've managed to get so far.
http://www.whatbird.com/forums/photos/nieblas_gallery/category1037/picture3553.aspx
If your bird was staying put on the branch, even after the cardinal landed, I agree with BHB. I'll bet it was a fledgling waiting to be fed.
There's a good bird-watching tip in all this. If, in summer or fall, you see a bird of a usually very active species, just sitting as if nailed to a branch or fence, wait a while and there's a good chance a parent will be along to feed it. If you look around you may also find siblings.
Swallows, for example, are another kind of bird difficult to photograph because they feed (and even drink) on the fly, and seldom perch in plain sight.This Summer I started to see a lot of them perching on fence wires and each time I did, it turned out to be a fledgling waiting to be fed. When they see or hear an adult coming near, they get incredibly agitated: flapping wings, squawking, and holding their mouths open wide. For the photographer, this is a great opportunity.
Here are a couple of albums showing this behavior in Barn and Rough-winged Swallows.
http://www.whatbird.com/forums/photos/upload_your_photos/category1060.aspx
http://www.whatbird.com/forums/photos/upload_your_photos/category1063.aspx
Chris
Chris from Denver