Birds of Summer
Summer’s here when long-legged herons flap slowly across the sky, appear streamside or long in the distance in the middle of a marsh, ghostlike, looking for dinner.
Or maybe you’ve spotted them up close in your own pond snatching koi!
Birds of mystery, Great Blue Herons taunt the imagination. Flighty and ethereal like shadows in the sky (they weigh only 5 pounds), they remain apart from human contact.
But why don’t we see them in winter? Do they fly south to join pelicans on the Florida coast? Or do they hibernate in the northeast like bats? The question spurred a conversation with Laura Erickson, science editor, at Cornell Lab of Ornithology (Lab), Ithaca, New York.
Erickson has the good fortune of studying a pair of Great Blue herons and their four offspring that set up nesting in Sapsucker Woods, just outside the Lab. The pair has stayed there into November and reappear in early March when open water returns.
In fall most Great Blue Herons head to the Atlantic coast and stay as far north as possible as long as there is open water for fishing. Although some fly to Central and the northern edge of South America, they are abundant in the southern states along the Gulf of Mexico and along the Atlantic Coast where, because the water doesn’t freeze, they over-winter as far north as New Brunswick, Canada. More birds are staying further north during the winter.
Great Blue Herons nest in dead trees or in pines where there is a break in the branches. They build big stick nests to lay eggs and raise their young. They nest in colonies, sometimes with hundreds of pairs. Because they’re so concentrated and because they eat fish, their acidic droppings kill the vegetation below them, including the live trees, which gives them more dead trees. It’s heron sprawl. Sometimes for decades they return to the same colony.
“In Sapsucker Woods, we have one pair and this is the first year ever that they’ve nested here so we’re really eager to see if this is the inception of a colony,” says Erickson.
The big birds usually build their colonies on islands or in wooded swamps that are fairly isolated and where they are protected from raccoons and other climbing animals that get their young. Even so, sometimes they fly afield to other waters for food, for instance when there’s a fish die off in their local dining spot.
The Sapsucker heron pair fished close to the nest when the babies were little, but as the babies grew the parents needed to find more and more fish and went further afield. “Now that the babies have fledged and are fishing with the parents, they are fishing close to the nest again where the food is most abundant.”
No one knows if the pair met before or at Sapsucker because the birds are not marked.
“Great Blue Herons pack an enormous wallop so they’re very difficult to handle,” she says. “The young birds, by the time they’re big enough to mark, become vulnerable to jumping out of the nest and getting hurt. The nests are usually inaccessible, so not a lot of people are doing research on them.”
Herons, eagles and osprey all feed their babies fish. Eagles and osprey are designed to carry fish in their feet. They carry it near their center of gravity between their wings and it doesn’t stall them out in flight unless the fish is too heavy.
Herons cannot do that. Their feet and beak are not designed to carry fish. They swallow their fish, fly back to the nest and regurgitate it. Eagles and osprey tear the fish apart with their beaks. Heron beaks are designed to catch fish but not to rip it apart, so they swallow it whole no matter the size. They always manipulate the fish after they catch it so they can swallow it head first – imagine if they didn’t!
They strike at fish with amazing speed and power. Their neck muscles are hefty. Their beak has to be hefty to slam into a fish. Most of a heron’s five pounds is in its beak and neck. So when they fly they have to pull that weight close to their wings where their center of gravity is. That’s why they fly with a big crook in their necks.
Sometimes herons stab fish with their lower mandible and the upper one just snaps on it. Sometimes they slam both parts of the mandible into it. That’s trickier because then they have to drop the fish and catch it again to swallow it.
Great Blue Heron populations are increasing in New York partly because:
• they perceive the sudden increase in bird feeders, which people perceive as koi ponds
• they have become habituated to people
• the kinds of fish they eat are doing well
Some birds that are around people often enough do become unafraid. “Those birds are the ones more likely to get bonked by an angry fisherman when they pull a fish out of their bucket and eat up all their bait or start going in backyards and eating people’s koi,” she says.
“A koi pond is not a natural thing and is not native to America” - Erickson
If a gardener has a koi pond, especially one that looks natural, expect to see the rest of nature – in the form of koi predator: Great Blue Heron. “The more natural a pond appears and feels to a heron’s perspective, the more inviting it is,” Erickson explains. “It just seems like another pond. Shallow water where they can wade makes it unfairly inviting to them. They just see it as a bird feeder.”
What to do? Design the pond more like a pool with deep water at the shoreline so herons don’t have a good place to stand, she advises. It will be less accessible.
Planting pond edges with emergent plants doesn’t help like it does with keeping geese away. A heron will walk right in. Plants may make the fish a little difficult to catch but the birds will figure things out because they make their living catching fish.
In summer, a bird fishes alone unless it is with its family. If it sees another Great Blue Heron fishing in a spot, it will look elsewhere. But birds very quickly figure out that decoys are fakes so the only way a decoy works is: 1) if people only put it out if a heron hangs around, and 2) are vigilant and move it from spot to spot so birds are tricked into thinking it’s real. Find them in garden supply stores. Fake floating alligators do not work.
Great Blue Heron Data
Weight: 4 – 5 pounds
Length, laid out: 46 inches
Wing span: 72 inches
Longevity record for a banded bird: 24 years
Nesting habitat: rookery, colony, heronry
Food: small fish, frogs, water snakes, small water birds, mice
Over-wintering grounds: Gulf of Mexico and Atlantic Coast
Protection: Migratory Bird Treaty Act
And FYI: If you think you see a white Great Blue Heron in the northeast, you do not. It is a Great Egret, slightly smaller with a yellow beak and black legs. They sometimes nest in Great Blue Heron colonies. The white morph is only in Florida.
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published September 08, 2009