What particular aspect of the birds' disappearance bothers the narrator the most?

The narrator is particularly hurt when she wakes to find that the birds have been disappeared. Most of her pain involves her beloved late father's position as an ornithologist and the wonderful memories she has of her father in this regard. She likes to think about the way in which she would use the excuse of bringing him lunch in order to spend time with him up in the observatory, sitting on his lap and looking at birds through his binoculars. The narrator worries that the birds' disappearance will negatively impact the treasured memories she has of times with her father.