Some species of reptiles nest communally; that is, females lay their eggs together in the same spot around the same time. Some? Maybe that should be “many,” says J. Sean Doody, an ecologist now at the Australian National University in Canberra.

Along with two colleagues, Doody performed an exhaustive literature review of the egg-laying habits of reptiles (and amphibians). It turned out that communal nesting had been reported in 345 reptile species—four times more than previously realized. (Even some dinosaurs may have laid eggs together, but Doody sensibly restricted his survey to living species.)

The numbers represent only a minority of known reptile species, but the egg-laying behaviors of many have yet to be observed. In certain families of Australian lizards, the team points out, communal nesters represent no more than 9 percent of all the species, but more than 73 percent of the species whose nesting habits are known.

Why a female reptile should lay eggs in another’s nest has been little studied. She would probably save the time and effort of searching for an appropriate site and digging a nest. And a larger, many-mom clutch may dilute her offspring’s risk of predation. But she might incur the reproductive costs of her hatchlings competing and exchanging diseases with their peers.

Striking a balance could account for the persistence in many species of females that nest sometimes together, sometimes alone.

The research is detailed in the Quarterly Review of Biology.

This article was provided to LiveScience by Natural History Magazine.