It's just a romantic analogy because I suppose when we are happily in love everything seems heightened. The sky seems blue, the sun shines and I guess birds singing is a happy and cheerful sound but it's not literally about birds appearing in front of you. Karen Carpenter was indeed one of the great singers of our time and it is sad that she has gone but she left so many beautiful romantic songs to remember her by. They really can paint pictures if you listen to them carefully and make you feel a range of emotions which take you back in time to places you might have forgotten. So although she didn't mean that birds were appearing in front of her she was imagining in her mind that they were part of the happiness she was feeling.