The location of a colony of breeding Great Blue Herons is called a heronry and it incorporates a large number of birds nesting in both older nests and building new ones. In this image you can see the nest on the right is still under construction. Recently built nests look like delicate platforms of interlaced dry branches, and older nests are bulky structures of different sizes. Usually, nests are about 1 m in diameter and have a central cavity 10 cm deep with a diameter of 30 cm. The herons sometimes line this internal cavity with twigs, moss, lichens, or conifer needles. Ordinarily, a pair takes less than a week to build a nest solid enough for eggs to be laid and incubated. Twigs are added mostly before the eggs are laid, but also when they hatch.