The GBHNR Colony

The GBHNRS colony has been monitored since 1976, when the heronry contained just 50 nests. Since then the colony has grown and fluctuated between 90 - 200 nests, with the peak being 203 nests in the early 2000s.

The colony is situated in a grove of mature Cottonwood trees in the Southwest area of the nature reserve and is gradually moving South thanks to a phenomenon called "associative nesting behavior".

The Pacific Great Blue Herons have adapted their nesting behavior in response to the increasing population of bald eagles - and can be seen doing so right onsite at our nature reserve.

Despite the fact that bald eagles are known to prey on heron nestlings and have been implicated in the recent decline of heron reproduction, herons have started to nest near breeding eagles. The hypothesis behind this change is that the territorial behavior of eagles provides protection for the herons. 

Observations have shown that nesting eagles repelled other eagles within a 250-meter radius of their nest site, creating a relatively safe space for the herons. 

Surveys also revealed that 70% of heron nests and 19% of heron colonies were located within 200 meters of eagle nests with high reproductive success. These herons had higher reproductive success compared to those that nested far from eagle nests.

The eagle nest on the nature reserve has fallen three times in recent years, and each time our heron colony shifts location to track closer to the eagle's new nesting location.

This unique adaptation is one of many ways that herons, and other wildlife, may adapt to ensure their young's best chance of survival.

• Herons choose a new mate each year
• Nest selections and courting starts in early March
• 3 - 5 eggs are laid in late March and hatch about a month later
• Incubation of the eggs lasts about 28 days
• It takes approximately 10 weeks for chicks to grow to a fully-fledged juvenile
• On average, only 1 chick per nest survives
• Eagles are a major predator of the colonies, eating both the eggs and chicks - however, having one pair of territorial eagles in the midst of the colony actually protects the herons from further predation from outside raptors
• Racoons are another predator of chicks, climbing the trees to eat eggs or chicks
• All of the trees herons nest in at GBHNRS are protected by fencing to keep the beavers from bringing them down
• Wood ducks, otters, beavers, and other wildlife are frequently sighted near the GBHNRS colony