Loons are aggressively territorial and ready to defend their corner of the lake the moment the ice goes out.
A common loon. Credit: Courtesy of Bob Duchesne

So, you think you know loons. OK. I’m going to throw out factoids and see if any of them surprise you.

You probably know that the annual Maine Loon Count took place last Saturday. This was the 40th year Maine Audubon has mobilized more than 1,600 volunteers to count loons. You might not know that the count takes place only in southern and central Maine. There are simply too few people to survey the remote lakes of northern Maine, especially when access is difficult.

Maine’s loons have faced an increasing number of threats over the last four decades. Adult loons have few natural enemies. A loon on a nest can be vulnerable to bald eagles, but attacks are rare, because the loon’s sharp bill is enough to convince most eagles it’s a bad idea.

However, eagles will grab chicks, and woe to the youngster that drifts too far from its parents. Chicks are also vulnerable to underwater predators, including snapping turtles. But loons and turtles have co-existed in Maine for at least 10,000 years, so turtle predation is clearly a minor threat. However, illegally introduced northern pike, and even large-mouth bass, can snatch a chick.

Small wonder that chicks often ride on the backs of their mothers.

Nest flooding is a much greater threat. Common loons are incapable of walking. They must nest directly on the shoreline, where they can scoot up on their bellies. Floods destroy their nests and eggs. You might have noticed that heavy summer rain storms are becoming more frequent.

Lake boaters can harm loons if their wakes wash up and flood nests, and a new class of boats is causing new worries. Wake boats are designed to produce waves big enough to surf behind. I predict you’ll hear more about them over the next few years.

Overall, Maine Loon Count data suggest we’re doing a better job protecting adults than chicks. Last year’s count continued an upward trend in the loon population. Roughly 3,000 loons were documented across southern Maine last year, double the first count 40 years ago. However, baby production remains flat. Adults may be doing better, but they’re raising only half the chicks.

Perhaps the biggest threat to loons is other loons.

Loons are aggressively territorial, returning to the same nesting area each spring, ready to defend their corner of the lake the moment the ice goes out. Young loons are not mature enough to breed until they are at least 5 years old. But once they reach that age, they may challenge an aging adult to battle, sometimes to the death.

The defending male has a lot invested in his territory. He has a mate and knows where the best nesting sites are. He is unlikely to flee from a younger, stronger attacker. About 30 percent of these battles result in his demise. Females also battle over territory, but not to extremes. The loser merely flies off to a nearby pond and tries again.

It’s better for everyone if mortal combat is avoided, so loons talk a lot. There are four typical vocalizations, categorized as yodels, wails, tremolos and hoots. Only the male yodels. It signals aggression and a willingness to fight, hopefully warding off rivals.

Both genders do the long, haunting wail. It keeps pairs and chicks in touch with each other over distances, especially at night. Loons do the tremolo to signal distress and danger, particularly when they feel threatened by eagles, boats and floatplanes. Hoots are just happy notes, uttered to each other close by.

Loons do not mate for life. Pair bonds may last several years, but mates go their separate ways in the fall. They must rekindle the romance each spring. If a male fails to return, or loses a battle, females quickly bond with the winner, or another available male.

Maine’s loons don’t migrate south for the winter. They head east to saltwater. Young loons cannot compete for territories, so they generally remain in the ocean year-round.

Once the territorial breeding season ends, loons can become quite gregarious again. It’s common to see large groups congregating on Maine lakes, often circling an area where fish are concentrated. Cooperative feeding makes it easier to grab a meal.

Loon nesting success rates are low, due to all the hazards they face. A pair may successfully raise a chick only once every two years. Still, loons live an average of 20 years, so that’s enough to keep the population stable — unless we humans screw it up.

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Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at mainebirdingtrail.com. He can be reached at duchesne@midmaine.com.