Bald Eagles are killing Maine’s Great Blue Herons

GREAT-BLUE-HERON-023-600x750Concerns over the demise of great blue herons in Maine are focused, in some parts of the state, on Bald Eagles. As DIF&W’s Danielle D’Auria told me, “bald eagles are definitely a predator and have been observed going after young (herons) in the nest, fledglings, as well as adults.  I think eagles can be a problem on a local scale.  A lot of our historic island colonies no longer have nesting herons but do have nesting eagles.  They are also known to nest on the same island, but we wonder how long that can occur.  I have volunteers who witnessed an eagle attack and drown an adult great blue heron at an inland colony.”

D’Auria is a wildlife biologist who works in the Bird Group of the Maine Department of Inland Fisheries and Wildlife. She focuses on understanding statewide populations of colonial wading birds, secretive marsh birds, black terns, loons, and other rare water birds. Since 2009, she has spent a majority of her time researching why great blue herons have undergone a decline along Maine’s coast.

In partnership with researcher, Dr. John Brzorad, from Lenoir-Rhyne University, and funding from the Maine Outdoor Heritage Fund, this spring DIF&W embarked on a great blue heron tracking project.  Their goal is to learn new information about Maine’s great blue herons with cutting-edge technology, while actively engaging students of all ages in every phase of the project, within Maine and beyond.

Here’s the agency’s recent blog post on this important project.

DIF&W Blog

Students and teachers from several schools across the state, in conjunction with the Maine Department of Inland Fisheries and Wildlife, are capturing and radio tagging great blue herons to learn more about herons and their habitats.

The student’s jobs, equipped with binoculars, minnow traps, and fish ID cards, is to locate a foraging heron in their area and then catch fish to use as bait to keep the herons coming back to the site.  IFW wildlife biologist Danielle D’Auria, and a small team of researchers will then capture the herons using foothold traps set near the bait, and tag each bird with a GPS transmitter to monitor their movements for years to come.

A trail camera captures images of herons visiting the bait site

The project is just one part of IFW’s ongoing research into the state’s great blue heron population.  By marking and following individual adults over several years, IFW will gather new information regarding Maine’s herons. The great blue heron is a Species of Special Concern for IFW due to the decline in the number of nesting pairs on Maine’s coastal islands from the 1980s to 2007. In order to learn more about great blue heron daily movements, habitat use, colony fidelity, migration routes, and wintering locations, the department began a citizen science adopt-a-colony program called the Heron Observation Network.  This new study will augment findings from that program.

The GPS transmitters on the herons transmit GPS locations via the cell phone network to an open source website (  Being solar-powered, they are expected to provide at least three years of data for each tagged heron.  Fully charged, the units collect 288 GPS points and 360 behavioral (accelerometry) tracings per 24-hr period. The data will be made public on for the students and other citizens of Maine to use in education and to help in making management decisions.   There is also a free app called “Animal Tracker” that allows anyone to track the birds (and other species) on a smartphone.

Students assist Biologist Danielle D’Auria by catching minnows for the bait bins

D’Auria is working with Dr. John Brzorad of Lenoir-Rhyne University in North Carolina who has been using these same transmitters since 2013 and has paired nearly 20 birds (great egrets and great blue herons) with school systems in five other states.

In Maine, the students involved in this spring’s field work range in level from grades 1-12 and are from the following schools: White Pine Programs in York, Harpswell Community School, Gray-New Gloucester High School, Nokomis High School in Newport, Old Town High School, Haworth Academic Center in Bangor, and Center Drive School in Orrington.  After the birds are tagged, D’Auria hopes to get students from every town in Maine following the great blue herons online and using the data generated by the solar-powered backpack transmitters in their classrooms.


Students are currently busy setting and checking minnow traps, identifying and measuring the baitfish caught, and placing the baitfish into a bait bin to see if a heron will feed from it.  They are using game cameras to “watch” the bait bins when they cannot be there themselves.  This is all being done in anticipation of the arrival of Brzorad and a few colleagues later this month, who will work with D’Auria to capture the herons.  When the traps are set, the researchers will watch from a blind until a heron steps into one of the traps.  They will then quickly retrieve the bird to take measurements and a blood sample for sexing, and attach the transmitter.  As soon as the bird is released, the data collection begins, and the students can start following and learning from “their” bird.

For more information on the Heron Tracking Project, including how to follow the great blue herons once they are tagged and resources for educators interested in using the data in their classrooms, visit this site.


George Smith

About George Smith

George stepped down at the end of 2010 after 18 years as the executive director of the Sportsman’s Alliance of Maine to write full time. He writes a weekly editorial page column in the Kennebec Journal and Waterville Morning Sentinel, a weekly travel column in those same newspapers (with his wife Linda), monthly columns in The Maine Sportsman magazine, two outdoor news blogs (one on his website,, and one on the website of the Bangor Daily News), and special columns for many publications and newsletters. Islandport Press published a book of George's favorite columns, "A Life Lived Outdoors" in 2014. In 2014, George also won a Maine Press Association award for writing the state's bet sports blog. In 2016, Down East Books published George's book, Maine Sporting Camps, and Islandport Press published George and his wife Linda's travel book, Take It From ME, about their favorite Maine inns and restaurants.