I am pretty sure they are toxic and so I wasn't sure about planting them in the pen at first. I have at least 2 plants in the pen that are poisonous, and I have seen the peafowl eat berries off of these plants and sometimes even the leaves. I trust their judgement on what they can and cannot eat and these plants have been in there for 4 or more years so I personally don't worry about it.
The Bronx Zoo has an indoor building called Jungle World. They housed a green peacock in part of the indoor tropical exhibit and there are several photos of this peacock next to some huge elephant ears. Zoos are very particular about what plants they should and should not use. I have also seen an aviary at the Jacksonville Zoo filled with ducks and other types of birds and there was a big patch of elephant ears in the aviary. They even had parrots in this aviary, and to me it seems like most toxic plant lists for birds are focused on parrots.
Rocking BAB Ranch has huge elephant ears over 6ft tall growing right next to some of their pens - even the young peafowl pens. The peafowl could easily reach through the fence and eat the leaves.
They will nibble at the plant, but they can tell it isn't good to eat. Of all plants for the aviary, grass is the best because they can eat it, but it is harder for them to destroy it (depending on pen size) because there is so much of it.