Wisdom by John Light. What can we learn from the bardo-states?

 “Are ghosts hungry for living human energies in the Tibetan Book of the Dead?”

I believe you are conflating two concepts of Tibetan Buddhism.

The Book of the Dead talks about what happens to a person after death. The venue for this experience is some other world dedicated to the purpose. It describes the types of experiences that can happen, and provides examples that have been brought back by people who have experienced death, either by going through the 49 day experience and coming out the other side, or coming back before fully dying (near death experience).

The other concept you seem to have brought in here is the Hungry Ghost Realm. This is one of the six realms thought to encompass all life. The idea of the realms is that our karma in one life determines which of the six realms we will be reborn in. Tibetan Buddhism teaches that the most desirable realm is the Human Realm, because it is the one where we have both the motivation and means to pursue the dharma.

Hungry ghosts are creatures who are “Incalculably frustrated by desires they cannot fulfill, hungry ghosts (pretas) are depicted with big bellies and tiny mouths.” They don’t typically populate the Human realm but we may run into them if we don’t take care of ourselves.

The beings in the short term realm described in the TBoD are typically highly confused as a continuation of their experience during life. Only beings who stabilized their minds during human life have a true experience in the 49 days after death, and the level of stabilization determines how long they can avoid confusion. When you get to the end of the 49 day experience/ordeal, you get to choose the realm and even the circumstances of your next life. Few of us have attained that level of stability, so most of us fall for some temptation and make a less optimal choice. A fully stabilized mind may choose to become a Buddha or return as a Bodhisattva.

https://quora.com/Are-ghosts-hungry-for-living-human-energies-in-the-Tibetan-Book-of-the-Dead