Forestry and Herons Can Mix
By Danielle D’Auria, Wildlife Biologist with MDIFW
Mention the great blue heron and most envision a large bird with long
legs and neck kneedeep in water slowly stalking its prey. These
wetland icons also rely on trees, both live and dead, for nesting.
These magnificent birds build large platform stick nests 8100 ft up
in trees and nest in groups, or colonies. In Maine, colonies occur on
coastal and freshwater islands, in beaver flowages, and in upland
settings. Their nests are built in mature hardwoods and softwoods and
can be in live, dead, or dying trees. Chances are, your property is
potential nesting habitat for these prehistoric looking and sounding
birds.
Great blue heron colonies may contain a few pairs to over a hundred,
often with multiple nests occupying the same tree. Colony habitat
preference is not completely understood, but they are most often
located within 2.5 miles of several important feeding wetlands; in
areas with few roads and little human disturbance; and within large
contiguous forest stands. Nesting in colonies helps in terms of
predator avoidance, but also makes them vulnerable to habitat loss.
Impacts to the colony and even brief disturbance events near the
colony can affect dozens of breeding pairs.
Maine’s great blue herons migrate south in winter to find icefree
feeding areas. As early as midMarch they begin to return to the
state, and by midApril many are setting up nests at colonies.
Individuals tend to return to the same colony location each year. In
Maine, some colonies have persisted for several decades.
During the nesting season (1 Apr – 15 Aug), the birds are extremely
sensitive to disturbances caused by human intrusion, noise, and
predators, and may even abandon a colony as a result. Their
sensitivity varies in relation to the stage of breeding; the
intensity, duration, and proximity of a new activity; woodland buffers
or topography; and preexisting uses on adjacent lands. The most
sensitive times tend to be just before incubation (early May) and
after the young are 46 weeks old (late June) and nearing fledging
(late July).
MDIFW has developed preliminary guidelines to help protect and
conserve great blue heron colonies. The main element of these
guidelines is to minimize disturbance to the birds during the nesting
season. To ensure this, we recommend a primary nesting buffer of
approximately 660 ft around great blue heron nests, in which all human
activity is avoided during the nesting period. Within approximately a
quarter mile from all nests, it is also best to avoid major
alterations to the landscape, such as land clearing, new road
construction, and permanent structures.
Forest management can be a compatible land use for great blue herons.
Timing considerations are critical; and fall or winter tree harvesting
is preferred. To ensure minimal impacts, harvest prescriptions are
best planned on site with a wildlife biologist. Management practices
that maintain or improve the integrity of the overstory and provide
for a continuing supply of mature trees favored for nesting are often
rewarded with continued colony occupancy.
Great blue herons also nest in snags in wetlands; in fact most of
Maine’s inland colonies occur in beaver flowages. A final
consideration for conservation of great blue heron colonies is the
protection of wetlands – both for nesting and foraging. Beaver
flowages need beavers to maintain them; allow beavers to persist in
these areas to some extent in order to create a stable water level
regime. Landowners can protect wetlands and streams and shorelines of
lakes and ponds by maintaining a minimum 75 ft nocut zone, and
adopting land use practices that protect water quality, limit erosion,
and conserve native wildlife and vegetation.
If you find a great blue heron nest, please contact MDIFW at (207)
9414466. Since 2009, we have tracked great blue heron colonies to
better understand their statewide population status. For more
information about this effort, visit the Heron Observation Network of
Maine’s blog at http://maineheron.wordpress.com.

Yellow Birch, Photo Credit: Doug McMullin

Maine Coast Heritage Trust colony, Photo Credit: Michael Merchant