Mongabay: Climate proves to be on the determining factors say scientists Clutch size varies greatly between bird species. Researchers now have a better idea why. Analyzing data on clutch size, biology, and habitat for 5,290 species of birds, a team of biologists — Walter Jetz (UC San Diego), Cagan H. Sekercioglu (Stanford University), and Katrin Böhning-Gaese (Johannes Gutenberg-Universität) — developed a model to predict variations in the number of eggs a species lays. They found …