Where Do Herons Nest? Heronries and Colonies Explained

Heronries: why herons nest together

Herons hunt alone, but most day herons and night herons nest in groups. A colony offers safety in numbers: many watchful adults are more likely to spot a raccoon or eagle, and a single tree full of nests is harder for one predator to empty. Colonies may also help birds find good feeding areas by following successful neighbors.

The great blue heron of North America is a typical colony nester. Its heronries range from about five to around 500 nests, and they are usually within a few kilometers of good feeding areas, often within about 4–5 km (2.5–3 mi). Some colonies hold only great blue herons, while others are shared with egrets, night herons, cormorants or other waterbirds.

In Europe, the gray heron (Ardea cinerea) also nests in heronries, and in continental Europe its colonies sometimes include purple herons and other species. In Britain, the British Trust for Ornithology has counted heronries every year since 1928, one of the longest-running bird surveys in the world.

The word rookery is also used for heron colonies in North America, though strictly it means a colony of rooks.

Where heron colonies are built

Large herons prefer tall trees near lakes, rivers, marshes or the coast. Nests are usually placed high up; great blue heron nests are often 9–21 m (30–70 ft) above the ground. Favorite sites are islands, flooded forests, beaver swamps and wooded areas that people rarely visit, all of which keep out mammals such as raccoons.

Herons are flexible when trees are scarce. Great blue herons have nested on shrubs, sagebrush, cacti, channel markers, duck blinds, artificial platforms and on the ground on safe islands. Gray herons sometimes use low bushes, reed beds, bramble patches, heather or cliff ledges.

Some colonies sit surprisingly close to people. A well-known great blue heron colony in Stanley Park in Vancouver, Canada, has held well over 100 nests next to a busy park entrance and tennis courts.

Not every member of the heron family nests in colonies. Bitterns and tiger herons are mostly solitary and hide their nests low in dense reeds or vegetation.

When do herons nest?

The nesting season depends on climate. Great blue herons return to their colonies from about December in warm areas such as Florida and California to March in Canada, and most eggs in the north are laid in March and April. In southern parts of the range, breeding can run from about November to April.

Gray herons are early nesters too. In Britain and much of Europe they breed mainly between February and June, so the nests are often busy while trees are still bare.

Building the nest

Males usually arrive first and claim a nest site, then court females with displays such as stretching the neck upward, raising plumes and snapping the bill. In great blue herons, pairs usually stay together for one season only, and most birds pick a new mate the next year.

The nest is a platform of sticks lined with twigs, pine needles, moss, reeds or dry grass. In gray herons, the male typically gathers the material and the female builds. Great blue heron nests may start around 50 cm (20 in) across, but after years of reuse they can grow to over 1.2 m (4 ft) wide and nearly 1 m (3 ft) deep.

Eggs and chicks

Both parents incubate the eggs and feed the chicks by regurgitating partly digested fish. Because incubation starts with the first egg, the chicks hatch a few days apart. The oldest chick is larger and stronger and often gets most of the food, so in poor years the youngest may not survive. To see what the parents bring back, read What do herons eat?

Heronries are loud, smelly places in late spring, full of clattering bills and begging calls. After their first flights, the young keep returning to the nest to be fed for a few weeks, then gradually disperse. Many wander widely before their first winter, as explained in Do great blue herons migrate?

Why heron colonies are sensitive to disturbance

Herons are most likely to abandon a colony early in the season, during courtship and egg-laying. Repeated visits by people, logging, construction or loud activity close to the trees can make adults leave their eggs, and a whole colony may move elsewhere.

Natural predators can have the same effect. Where bald eagles repeatedly attack a heronry, the herons may abandon it, and raccoons climbing into nest trees can destroy many eggs.

For this reason, wildlife agencies often advise people to watch heronries from a distance, using binoculars, and to stay well away from nest trees during the breeding season. In the United States, active heron nests are protected under the Migratory Bird Treaty Act, and in the UK all wild birds’ active nests are protected under the Wildlife and Countryside Act 1981.