Adult great blue herons have few predators besides bobcats, coyotes and occasionally large raptors, but heron eggs are susceptible to predation by crows, gulls, ravens, foxes and raccoons. Great blue herons are quite large when fully grown, which reduces their risk of falling victim to predators. Their eggs, however, are much more vulnerable and face risks from terrestrial mammals and other birds.
Great blue herons build nests relatively high off the ground, frequently in tall trees and toward the tops of telephone and utility poles. This helps keep their eggs away from some mammals such as foxes and coyotes. Despite parents' best efforts, however, the mortality rate for great blue heron eggs is somewhat high. While building nests keeps heron eggs safe from ground predators, it offers little protection from airborne predators, which are primarily large birds such as hawks, vultures, eagles and other raptors. Sometimes groups of smaller birds, such as ravens and crows, attack heron nests in flocks and take eggs in the process. Heron nests are sturdy in build and often fortified with soft materials, but they offer hatchlings little protection from the elements. Therefore, environmental conditions such as heavy rain, snow and cold winds can also kill juvenile herons. Lastly, pollution and toxic chemicals such as DDT pose long-term risks to certain populations too.