Why do blackbirds lay 4 eggs?

Blackbirds typically lay four eggs as it strikes a balance between maximizing reproductive success and managing the energy costs of raising their young. Laying four eggs allows for a sufficient number of offspring to survive while reducing the strain on the parents in terms of food and care. Additionally, this number increases the chances of at least some chicks surviving to fledging, even if some eggs do not hatch or chicks do not survive. This strategy reflects an evolutionary adaptation to optimize the survival of the species.