Great blue herons’ absence is a great blue mystery

Great blue herons are the tallest birds in Maine and the largest herons in the New World.
Bob Duchesne
Great blue herons are the tallest birds in Maine and the largest herons in the New World.
By Bob Duchesne, Special to the BDN
Posted April 19, 2013, at 12:42 p.m.

As I get older, I seem to be misplacing things more often. For instance, it seems that I have misplaced several hundred great blue herons. That’s not easy to do when you consider that it is the tallest bird in Maine and the largest heron in the New World. The goliath heron of Africa is larger, but not by much.

We used to have more than a thousand pairs along the Maine coast, but their numbers have plummeted and we don’t know why. In the 1970s, around 1,200 pairs were known to nest near salt water. From 1983 to 1995, the numbers dropped by half. By 2009, we were down to only 400 pairs.

It shouldn’t be happening. Numbers have been increasing across much of North America as beaver populations have recovered. Beavers create good habitat for herons, which stalk fish, amphibians, reptiles and insects. Herons even eat small mammals and other birds — whatever is within reach. Herons are equally comfortable in salt and freshwater habitats. They’re not picky, so a reduction in food resources doesn’t seem to be the problem.

Whenever a top carnivore shows rapid declines in population, environmental factors are suspected. Just as DDT nearly wiped out the peregrine falcon and decimated eagle and osprey populations, perhaps another toxic chemical in the environment is building up in the food chain, poisoning herons. If so, we don’t yet know what it is. Almost none of the chemicals used in America have been tested for long-term toxicity, the result of outdated chemical policy at the federal level that hasn’t changed since the 1970s.

Maybe the problem is eagles. It takes a valiant eagle to attack a bird that stands taller and wields its sharp bill like a switchblade, but bald eagles aren’t known for being shy. As their populations have increased, we’ve seen a simultaneous decrease in the number of herons. There are plenty of anecdotal observations of eagles attacking herons.

I’ve seen it myself. A dozen years ago I was paddling my kayak on West Shirley Bog when I heard a shriek above. Upon looking up, I beheld the most elegant aerial combat I’ve ever witnessed. An adult bald eagle was trying to knock a great blue heron out of the sky. The heron was over water and had nowhere to run, nowhere to hide. Time after time, the eagle attacked and the heron dodged high above me.

As soon as the heron was within reach of the shoreline, it plummeted to earth. I was amazed at the speed of the descent. I was even more astounded that the heron was able to hit the brakes before splattering on the forest floor.

Once on land, the heron regained the advantage. The eagle alighted in a nearby tree, glared for about a minute and then flew off in disgust.

Some eagles certainly succeed. Perhaps the increase in bald eagles, especially along the coast, is merely driving the herons inland.

That’s a possibility that Danielle D’Auria is looking into. She is the Maine Department of Inland Fisheries and Wildlife biologist who has the duty of figuring this out.

With the tightening of the state budget, D’Auria is relying on a network of volunteers to seek out and monitor heron nesting sites. The study is called the Heron Observation Network of Maine, or HERON for short.

Participation of volunteers does more than just lend people power to the department. Their donated time can be used to help meet federal requirements for matching funds. Private-sector grant committees also prefer to fund projects with demonstrated community support. This kind of citizen science helps concerned citizens study and conserve wildlife without relying on the state treasury. The Maine Loon Count is another example.

This year, DIF&W will expand its network of volunteers to examine the question of whether herons have relocated inland. D’Auria’s corps of citizen scientists will also watch more closely to see how well nestlings are being nourished to adulthood.

More volunteers are needed and the time requirement is small. You can find more information at maineheron.wordpress.com. The herons will help you. They have nested in trees and in colonies to make observation easier.

If you can’t volunteer, you can donate. Go to maine.gov/ifw and visit the online store. The heron stickers are inexpensive. Buy a Birder Band. It attaches to binoculars and aids recovery if they are ever misplaced. It’s the best $20 I’ve spent this year.

Bob Duchesne serves as a Maine Audubon trustee and vice president of its Penobscot Valley Chapter. Bob developed the Maine Birding Trail, with information at www.mainebirdingtrail.com. Bob can be reached at duchesne@midmaine.com.

 

http://bangordailynews.com/2013/04/19/outdoors/great-blue-herons-absence-is-a-great-blue-mystery/ printed on December 18, 2014