Ostrich eggs are the largest of all eggs, though they are actually the smallest eggs relative to the size of the adult bird - on average they are 15 cm (5.9 in) long, 13 cm (5.1 in) wide, and weigh 1.4 kg (3.1 lb), over 20 times the weight of a chicken's egg and only 1 to 4% the size of the female. They are glossy cream-coloured, with thick shells marked by small pits. The eggs are incubated by the females by day and by the males by night. This uses the colouration of the two sexes to escape detection of the nest, as the drab female blends in with the sand, while the black male is nearly undetectable in the night.