Exact pattern varies geographically. Ostriches form bisexual groups with a complex structure. Territorial males compete for flocks of 3 to 5 hens. Elaborate displays, including hisses and other noises, are often used by males to intimidate each other. Once divided into mating groups, ostriches in some areas use communal nests to hold anywhere from 15 to 60 eggs. The nest is a hole scraped in bare ground. The average egg is 6 inches in length, 5 inches in width, weighs about 3 pounds, and is shiny and whitish in color. Eggs take approximately 40 days to hatch. Caring for their eggs is divided up between males and females. Males watch over them during the night, and the various females of the mating group take turns during the day.