Females have between four and five eggs at a time. Before hatching, there is about fourteen days of incubation. The eastern bluebird has been decreasing in population over time. Despite the fact that many eggs are laid, the birth's success rate is low. One thing that can be the source of that phenomenon might be the introduction of the common starling from Europe. That kind of bird is a strong competitor fighting against eastern bluebirds for natural cavities. If they are fighting every day females would not be able to lay their eggs because they need a calm location to do it. However, the situation could be worse without nest boxes to help eastern bluebirds find a safe location.