Great Blue Heron (Ardea herodias)

Prepared by Paul Nicholson, February 2022.

Left: an adult Great Blue Heron is pictured fishing at The Coves Environmentally Significant Area near central London. Right: With a wingspan of 183 cm, the Great Blue Heron is Southwestern Ontario’s seventh largest bird. All photos by Paul Nicholson.

The Great Blue Heron is the largest of London’s herons or “waders.” Because of their size, they are relatively easy for us to see and identify. This species is named for its size and also the grey-blue feathers on its back, wings, and tail. Although the bird is rarely misidentified, some field marks are still noteworthy. Adult birds sport black head plumes. Juveniles have brown streaks on the front of their neck and chest. The bird’s huge and powerful bill is wielded to catch prey. During the birds’ courtship season in the spring, the bills become a deeper yellow.

The vocalization of the Great Blue Heron is far from pretty. Instead, it is a primordial croak.

Listen to the Great Blue Heron call below:

Young Great Blues have heavy streaking on their neck and chest.

Learn more about the Great Blue Heron’s life history

The Great Blue’s diet is varied. They feed on fish, frogs and other amphibians, reptiles, small mammals, and even other birds. They usually forage on their own in still water. You might see one in the shallow water of the Thames River. They are frequently seen in the pond waters of Komoka Provincial Park on the north side of the Thames.

Interestingly, although these herons are most often solitary, they nest communally in heronries. Occasionally during migration or while overwintering, Great Blues will be seen together. During a January 2022 Ontario Filed Ornithologists’ bird hike for example 49 Great Blues were observed together in Essex County. Most of the Middlesex County Great Blue Herons do migrate south into the U.S. but some opt to stay in the London area. As long as there is some open water, they are able to hunt for food.

Citizen science data show that Great Blue Heron population numbers have been mostly stable across most of North America over the past decades. Chemical pollutants do constitute an ongoing threat the birds and their habitats however.

There are a number of Great Blue Heron communal nesting sites near London.

Help make London more Great Blue Heron friendly:

Don’t leave litter or fishing line by rivers and ponds. If you find some, consider collecting and disposing of it.
Don't dump pet goldfish in bodies of water. Goldfish are an invasive species that compete with other organisms that provide food for birds including Great Blue Herons.
Record heron sightings on eBird or iNaturalist and contribute to community science.
Support the protection of wetland habitats and support efforts to address climate change.
Avoid use of pesticides and reduce your ecological footprint as much as possible.