Various species of birds from the genus Agaporis possess differing behaviors. These behaviors differ in a way that can be used to infer how the species are related and how they have evolved over time. For example, the three lovebird species considered to be the most primitive all build simple nests in preexisting cavities. The three middle species all build elaborate nests with tops, and one even digs out a cavity for the nest. The four modern species build cuplike nests: These nests are more complex than those built by the primitive species but less complex than those built by the middle species. William Dilger conducted an investigation to show that the nest-building behaviors of these birds were genetic rather than learned behaviors. In his investigation, Dilger used two different species of lovebird that readily mate with each other-Fischer's lovebird and the peach-faced lovebird. Fischer's lovebird is a species of moder lovebird while the peach-faced lovebird is a slightly more primitive species. Fischer's lovebird carries small pieces of nesting material in its beak. The small size of the nesting material is the reason for the simpler cuplike nests of Fischer's lovebird. The peach-faced lovebird cuts long strips of nesting material, which is then tucked into the feathers on the back of the bird. These long strips of nesting material will often fall out of the bird's feathers. However, the long strips of material allow the peach-faced lovebird to build an elaborate nest. The hybrid offspring of these two species has difficulty building nests. The hybrid offspring will cut long strips of material like its peach-faced parent. However, the hybrid offspring will attempt to carry the material in its beak and have difficulty flying. If it does attempt to place the material in the feathers of its back, the material falls out because the bird does not properly secure the material in its feathers.