In "The Story of an Hour," what is ironic about the sounds Mrs. Mallard hears after she has been told of her husband's death?

A reader would likely assume that a woman having just heard about her husband's sudden and dramatic death would be overcome with painful emotion, capable of seeing and hearing only things that are dark and sad.  However, Mrs. Mallard, quite unexpectedly, sees and hears signs of life and promise and hope.  Sitting, alone in her room after hearing this presumably sad news, Mrs. Mallard looks out the window, and "She could see in the open square [...] the tops of trees that were all aquiver with the new spring life [....].  The notes of a distant song which some one was singing reached her faintly, and countless sparrows were twittering in the eaves."  It is ironic that, after just learning of her husband's death, Mrs. Mallard hears the sounds associated with new life: birds and people singing joyfully.  Spring is the season most associated with life, and her ability to discern only the lively sounds associated with this season is ironic given the morbid news of Mr. Mallard.