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Loon Migration Update: May 4, 2000

Today's Report Includes:

LOON-er Landings

It seems the loon migration is almost complete. There are fewer loon sightings to report today, compared to 119 in our last report. Just about all loons are back on territory, filling the north with their haunting calls and brilliant colors. A few stragglers are still arriving in the far north, but for the most part they're settling into nesting.
Time for Nesting and Nurseries
During breeding, loons need suitable nest sites. A loon pair prefers building their nest where it floats or is at the water's edge by a drop off steep enough so they can arrive and depart underwater. The best nest sites also include some overhead cover to hide eggs from the eyes of avian predators, and shelter from wind and waves. If a pair loses an egg or chick to predation, they make a replacement nest in a new site.


Courtesy of James A. Anderson

Loons work on building their nests all through incubation, and nests are often used over again. A loon pair has just one brood with two chicks each year. The eggs are olive-brownish green with a few dark speckles. Eggs measure 3.5 inches (89mm) long, and hatch from 26 to 31 days after incubation starts. (Each egg hatches at a different time.) Chicks leave the nest and are on their own at the age of 75 to 80 days.

Besides their nest site, loon pairs also need a "nursery" pool. Often the nursery pool is a quiet bay, and it can be a fairly long swim away from the nest site. The nursery pool must contain water that's clear enough for the loons to spot their prey. At the same time, the water must be shallow enough limit the size of fish and turtles that prey upon loon babies, reasonably free of scouting eagles and gulls, and bountiful enough to furnish an eleven-week supply of food for the two chicks they will hatch. The best nest territories offer a view of neighboring territories and a pool with little wind and calm water. This helps keep the babies from being separated from the parents and open to predators.

At first the chicks eat plant material, crayfish, aquatic invertebrates and small fishes. As they grow, they eat more and more fish, until finally fish become their major food items. The young can supply much of their own food by the time they are eight weeks old. Adults, including those with young, leave their territories for more and longer periods as the summer goes on.

The chicks spend up to 65% of their first week being carried on the back of an adult, but they SWIM from the nest to the nursery when they are less than two days old. When on their parent' back, the chick is capable of clamping its bill onto the adult's feathers to hold on.

We wish the loons well this summer, as they build nests, incubate eggs, and their raise babies.

Analyzing Wisconsin's Loon Migration 2000
With the arrival of over 100 loon sightings from Wisconsin in one short month, you are probably as exhausted as the loons! If their migration seems like a blur, it would help to focus in on this single state, and see what can be learned from the large volume of data.

When do you think loon migration into Wisconsin peaked this spring?

Don't Hold Your Breath!

How are loons like submarines? They are long, slender, and streamlined, with two powerful propeller-like legs attached of the rear of their body and tipped with webbed feet. They float low and have relatively solid bones (loons weigh about 6 to 8 pounds). Like submarines, they can dive deep. Their bodies are built for fast underwater swimming, hunting, and diving--which makes them fascinating to study.

People watching loons are often amazed at how long they can stay underwater. When you see a loon dive, you'd better not hold your breath until it comes back up. Most loon dives last between 8.5 and 60 seconds. But under stress, loons can remain underwater for about three minutes. Some people have watched a loon dive down and not come back up for longer than 5 minutes. And someone once clocked a loon's dive at 10 minutes! However, many ornithologists believe these records are not accurate. (How long can YOU hold your breath?)

Loons usually dive head first, but they can also sink slowly into the water. When they want to, loons can also float as lightly as ducks! How do they manage it? Like all birds, loons have balloon-like air sacs that hold a large volume of the air they breathe. When a loon fills the air sacs with air, its body becomes less dense and more buoyant, allowing it to swim high in the water. As the loon forces air out of the sacs, its body becomes more and more dense, and it sinks lower and lower into the water.

If a loon were trying to elude a motorboat, do you think it would be more likely to DIVE or to SINK into the water? How about if the loon were trying to elude a distant Bald Eagle?

Try This! Sink or Swim
To understand how loons can use their internal air sacs to sink and float, try this experiment:

Back on Territory
Response to Challenge Question #15
Last time we asked, "Some loons don't arrive until after territories have been established and nesting has begun. What might be some reasons?"

No one knows for sure. Loon authority Judith McIntyre says: "I suspect these may be younger birds, perhaps wearing their black and white feathers for the first time. Many are nonbreeders and remain unpaired throughout the summer."

She takes it further by saying: Second-year immatures molt their flight feathers later than adults do, and are flightless early in the summer. Is it possible that the remigial molt moves up a little earlier each year until loons reach adulthood, so that three-year-olds molt in April or May, and have just finished molting when they arrive?" There is still much to learn about loons!

Answer to Challenge Question #16
Challenge Questions 16-19 were all asked in connection with the lesson "Mercury Alert!" Challenge Question #16 asked: "In Little Rock Lake,
  1. approximately how many times more mercury do zooplankton have than phytoplankton? (About 3.5 times)
  2. about how many times more mercury do fish have than zooplankton? (About 4 times)
  3. about how many times more mercury do loons have than fish? (About 6 times)

Discussion of Challenge Question #17
"What factors do you think would contribute to the mercury amounts found at each level of the food chain?"

Some possible factors are the age of the animal because it would affect the length of time the mercury accumulates; the size of the animal; and the amount of food needed for its existence.

Answer to Challenge Question #18
"In one Ontario study area the yellow perch were found to have 360 ppb of mercury. How many times more mercury was found in these fish than in the fish in Little Rock Lake?

Answer: Over 1.5 times more.

Discussion of Challenge Question #19
"What kinds of things in our environment contain lead?"

We may have lead around our homes or school buildings without knowing it because we can't see, taste, or smell lead. There may be lead in the dust, paint, or soil in and around our homes, or in our drinking water or food. Someone who works in construction, demolition or painting, with batteries, or in a radiator repair shop or lead factory, or with a hobby that involves lead may unknowingly bring lead into their home on their hands or clothes. People may also be tracking in lead from the soil around their homes. Soil very close to homes may be contaminated from lead paint on the outside of the building. Soil by roads or highways may be contaminated from years of exhaust fumes from cars and trucks that used leaded gas. Because it does not break down naturally, it can remain a problem until it is removed.

Before we knew how harmful it could be to living things, lead was used in paint, gasoline, water pipes, and many other products. Now that we know the dangers of lead, house paint is almost lead-free. Leaded gasoline is being phased out, and household plumbing is no longer made with lead materials.

Midnight Loon Search: A Closing Story From Our Expert
A Night Capture

Mark your calendar for May 12 when our loon expert, Ted Gostomski, answers your loon questions on the web. Meanwhile, if you read the biography of Ted, our Journey North loon expert, you know that his favorite work experience was the chance to band loons on Isle Royale, a National Park and wilderness island in Lake Superior. Here's how he describes it:

"My primary job was to be the driver of the boat, and we would leave the dock at around 10 PM. After arriving at the place where we knew loons were, we would shut the boats off and sit in the dark, floating on the calm waters of Lake Superior in some secluded bay or cove. Islands rose from the lake along the darkened horizon, and spruce trees reached to the stars. We would play a tape of a loon call in order to locate the birds and then again sit quietly and wait for the real birds to answer. When that answer came, it was something of a religious experience, and when our spotlight found the family floating off in the distance, the excitement was intense.. . .It's hard to explain what it feels like to be out in a boat in the middle of the night on the largest lake in the world, but the experience is one I will always cherish and is what I think about when I find myself embroiled in the rush of "mainland life."

This year, Journey North reported about radio telemetry, a new way beyond banding for scientists to learn more about the mysterious loon. Who knows what new events and observations we'll all be sharing in our next season of Journey North. We hope you'll be back to find out!

Journey North
Year End Evaluation
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Have a Wonderful Summer!
We hope you enjoyed learning about this spectacular diver's journey north. See you next year!

This is the FINAL Loon Migration Update for Spring 2000.

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