One day, years ago, I was collecting data on the behavior of the Jamaican twig anole, A. valencienni. As I was watching a female, to my surprise, she entered a hole in a tree trunk, and then emerged a little while later. To my amazement, I then saw another valencienni do the same thing! Overcome with curiosity, I approached the tree, peered into the hole, and spied to my astonishment a large number of what seemed to be anole eggs. I was not aware that communal nesting—in which multiple females lay their eggs in the same place—is known in a number of anole species, including A. angusticeps, A. bartschi, A. lucius and A. valencienni. The seminal work on the subject is still Rand’s 1967 Herpetologica paper.
A recent paper adds another species to the list of known communal nesters, the first from Central America of which I’m aware.
Montgomery et al. located seven nests containing 47 eggshells and 67 unhatched eggs on the side of large moss- and vegetation-covered boulders along the side of a stream in Panama. Hatching the eggs in the laboratory confirmed that they belonged to A. lionotus, one of the Central American “aquatic” anoles always found immediately adjacent to streams.
Why anoles nest communally is unclear, though the best guess is probably that good sites are limited, combined with the fact that females, which can lay a single egg every 1-2 weeks, may return to the same place repeatedly (though this has not, as far as I’m aware, been documented).
Actually, surprisingly little is known about all aspects of anole nesting and egg biology.