Sunbathing Black Phoebes

In between visits to the Black Phoebe family I have been following at my friend's property, I visited a second pair of Black Phoebes that appear to be nesting under a RR bridge over the Arkansas River east of Florence. While watching the pair, I was surprised to see one Black Phoebe, then the other, engage in sunbathing. Since these birds stay about 75 feet across the river, I wasn't able to get a good enough pic of this behavior to post.

Over the hundreds of days I have spent observing Black Phoebes in Fremont Co, I have never seen them engage in sunbathing. Though some other species of birds are known for sunbathing, Birds of North America online states that there is no information on sunbathing by Black Phoebes. I suspect there is a paucity of knowledge about this species. SeEtta