Allowing someone else into our world, making them a confidant, or an intimate in our own lives is simultaneously a means of expanding ourselves and of letting go. At a certain point we trust others who are close to us. We trust them to be gentle when we are fragile and to push us when it is appropriate - even if we may not know when that time is. Relationships of trust require tending, practice, negotiating norms and boundaries. Loss, then, somewhat impoverishes our world. The space of relationship-as-expansion disappears.
Helen Macdonald's book is about training a goshawk. But it is also, and perhaps more so, about what loss can do and how we see that loss manifest in our endeavors and in ourselves. Macdonald shows us how the experience of losing her father is poured into her developing relationship with the goshawk, whom she calls Mabel. Macdonald clearly understands that the type of relationship she has with Mabel is of a different character than what she had with her father. She does not conflate her sense of emotional connection with the hawk's. Yet, it would be a narrow understanding of relationships - of any kind - to denigrate the one between a person and a bird as somehow less worthy of our examination and reflection.
Taking solace in a relationship, say between human and animal, does not mean that it replaces the relationship lost. The world is expanded when we bring others into it. Whether they be human or otherwise. How it is expanded says more about the interactions of the relationship than it does about either participant.