Did actors playing different ape species refuse to eat together during the filming of Planet of the Apes in 1967?

Question

According to Futility Closet (attributed to Planet of the Apes Revisited, 2001):

During the filming of Planet of the Apes in 1967, Charlton Heston noted “an instinctive segregation on the set. Not only would the apes eat together, but the chimpanzees ate with the chimpanzees, the gorillas ate with the gorillas, the orangutans ate with the orangutans, and the humans would eat off by themselves. It was quite spooky.”

James Franciscus noticed the same thing filming Beneath the Planet of the Apes in 1969. “During lunch I looked up and realized, ‘My God, here is the universe,’ because at one table were all the orangutans eating, at another table were the apes, and at another table were the humans. The orangutan characters would not eat or mix with the ape characters, and the humans wouldn’t sit down and eat with any one of them.

Is the above story true or fiction?

Answer 1

According to Natalie Trundy, as published in Starlog magazine, issue 290, September 2001 :

TRUNDY:...During the filming, at lunchtime the gorillas would eat with the gorillas... the chimpanzees would eat with the chimpanzees... and the other ones would eat together, too. One group here, one group there! Except for the stars, of course.

STARLOG: This was on the first movie?

TRUNDY: This was on all of them!

Also, the Heston quote is in this 1980 Omni magazine:

During meal breaks," he remembers, "I noticed that the humans would tend to eat together, and not only did the apes eat by themselves, but the gorillas would eat with gorillas and the chimpanzees with chimpanzees. They did it instinctively" Heston maintains that while this "natural" segregation was eerie, it had the creative by-product of heightening the feeling of alienation that his part required.

Film Review (1997) separately quotes Heston as saying:

Heston observed that a fascinating social behaviour emerged during the filming of Planet of the Apes. "There was an odd personal segregation. The gorillas sat at one table at lunch, the chimpanzees at another and the dominant species, the orangutans, sat at a third. Nobody dictated this, they just did. I usually had lunch with Frank or my wife. They couldn't eat anything but liquid food because of the make-up, so they probably didn't want to have to sit and look at the chicken salad.