It is rather whimsical too. There is plenty more than singing involved, especially if there is a family of Blue Jays in the area. Songs and size. You may have noticed that often the smallest birds have the most interesting songs. The various wrens, for example, are among the smallest birds in North America, but they have incredibly loud voices and many complex songs.
Eagles are loud, but they have a limited vocabulary.
While this phenomenon has not been explored, one obvious conclusion is that the eagle doesn't need to be a good public speaker when it can rip most avian competitors to shreds. On the other hand, the tiny wren's verbosity helps it survive in the habitats where they live and compensates for lack of brawn.