All righty, so.. From even just my short time reading, I can see a few interesting observations regarding the Tangata Manu and the anthropomorphic
Bird people from Easter Island.
Firstly, I am going to venture that there were no alien Birdmen, or women. My interpretation is that the Birdmen (Tangata Manu) are representations of
individuals from the community who dawn the appearance of a bird for certain ceremonies, rituals and maybe even games.
Here is a photo of two statuettes. They are the Tangata Manu, or Birdmen of Easter Island. If we look at them, we can see that the "beaks" of the
birds clearly rest on top of the statuette's nose. I suppose it is possible that a Bird humanoid could have both a nose and a beak, but to me that
seems unlikely. So, here we have an example of the Birdmen being humans dressed in a bird outfit.
In the next image, we also find instances in which the inhabitants of Easter Island made clothes that resembled birds; Head dresses made of
feathers.
Again, more instances in which the Islanders wore clothes made from feathers. In this picture, you see an islander as well as a famous carving from
the Isle. Note the similarity in appearance between the two in the head dresses.
We also find many images of Manutara, which is the corner stone of the bird cult Tangata Manu. He's shown below as he is usually depicted, and a
quick Wikipedia search gave this of Manutara:
Manutara is the Rapa Nui language name for the Grey-backed Tern and Sooty Tern birds. Both arrive at Easter Island and hatch their eggs on the island
called Motu Nui, an event that was used for an annual rite called Tangata manu.
It's my guess that the pictures from the OP are of the Tangata Manu, or Birdmen of Easter Island. Specifically, they are photos of depictions of the
Manutara.
Sadly, no aliens

Still a very beautiful place though if you ask me.