Common Loon Migration Update: March 27, 1997
Dr. F.G. IrwinLoons are on the move! Since our last update on March 13th, several early loons have been spotted in 13 different places. Our first loon migration data chart is attached below. Here are comments from observers in Ontario and Wisconsin:
Meanwhile, Lucy Vlitstra has been watching loons prepare for migration on their wintering grounds in Apalachicola Bay, Florida. Here are her latest field notes:
To: Journey North
"Loons are flying! After the long flightless period adult loons are finally in the air. I have seen them only in singles heading along the coast in the evenings. I can't say whether they are really taking off for migration because they're not traveling over land and other reports of migratory behavior suggest they migrate in small groups. The flying loons that I see may be traveling to pre-migratory congregations or simply 'pumping up' their muscles for the long flight. I don't know. All of the ones I have seen are flying relatively low suggesting that they had not come any great distance.
"Also of note, nearly all adult loons are in some stage of breeding plumage. It is not uncommon to see one in FULL breeding plumage foraging among the half-brown-and-white half-black-and-white molters. I have also noticed a small decline in numbers in the Bay, suggesting either loons are leaving the Bay for other areas down here or that they have headed north.
"Things have been pretty exciting. I look forward to seeing what happens when most-all adults are in alternate (i.e. breeding) plumage. I wonder if they will all leave at one or if they will trickle away. This week I plan to travel to nearby bays to look for large aggregations of loons preparing to migrate."
Talk to you soon,
Here's a note from another of the loons' Florida neighbors, manatee biologist and bird watcher Dr. Bruce B. Ackerman:
"We also had some high loon mortality in 1996 and 1997 in southwest Florida.
Loons seem to be more susceptible to red tide in the late winter, when they are molting and can't fly away from it. Most of the other seabirds are not immobilized by molting."
As you may know, last year's red tide outbreak in Florida resulted in massive deaths of the endangered Florida manatee. Toxin from the microorganism Gymnodinium breve, which is commonly known as "red tide", killed 151 animals in Southwest Florida from March to April 1996. Dr. Ackerman is one of the principle biologists who helped identify and study this problem in Florida.
In our last report, we asked Challenge Question # 4: "How do you think mercury gets into a loon's body? That is, how might mercury from the atmosphere end up in a loon?"
As students at Valley View Elementary School in Columbia Heights, MN recognized, mercury enters the loon's body through the aquatic food chain:
"We think loons get mercury poisoning by eating the fish that live in the
polluted waters. The mercury gets from the atmosphere into the water when
it rains. Then the mercury gets into the things that the fish eat and they
have mercury in their bodies."
The following series of Questions and Answers about mercury was provided by loon biologist Dave Evers. Evers credits much of his knowledge about the effects of mercury on loons to his work with Dr. Mike Meyer. Dr. Meyer has been studying the impacts of mercury exposure on loons in north eastern Wisconsin for the past seven years. He works for the Wisconsin Department of Natural Resources Bureau of Science Services and his specialty is in toxicology (the study of how toxic chemicals effect animals).
Dr. Meyer's mercury study examines connections between loon chick production, lake acidity and levels of mercury in adult and juvenile loons. As a result of the intensive work on loons in the mercury study, Wisconsin now supports the largest population of color banded loons in the world. Because the birds have individual color bands on their legs, scientists are able to identify each bird and along with data on mercury, data on behavior, mating, return rates of loons to lakes and other natural history information have been collected.
Here is more information about mercury and loons, provided by Dave Evers. After reading this series of questions and answers, can you answer Challenge Question #5?
Challenge Question # 5
To respond to this Challenge Question please follow the instructions at the end of this report.
Question: "How might mercury from the atmosphere end up in a loon?"
Evers: "Most, if not all, of the mercury entering aquatic systems is deposited from the atmosphere. Once in the water, it is concentrated in fish, the loons' primary prey.
Question: What kinds and sizes of fish are the worst sources of mercury for loons?
Evers: "Larger fish are worse because they concentrate the mercury since they are at the top of the food chain. Walleye are worse than minnows, for example. We know that mercury bioaccumulates through the trophic levels and in individuals."
Question: Will mercury be passed by an adult loon to the eggs? Does it have an effect like that of DDT on eagle eggs?
Evers: "Yes, the mercury is passed on to the egg, and the chick will have higher levels. The effect is not eggshell thinning, as with DDT, but is lack of motor coordination in chicks because the mercury affects their nervous system."
Question: Does intake of mercury cause loons to live shorter lives? What are their normal life spans?
Evers: "Loons have reproductive FAILURE if they eat fish with higher than .4 parts per million. Reproduction is impaired when the fish have .3 parts per million. (Reproductive failure means the young do not survive.)"
Question: What could we expect to learn about the kind and amount of food that a loon eats just before migration--does it "stock up" on fish that might have more mercury in them at these times, or is the summer loon forage a higher source of mercury?
Evers: "We believe that fish eaten in the summer are the problem. Here's why: Feathers can be tested for mercury, and feathers that have grown during the wintertime (on the wintering grounds, before migration) do not seem to contain high levels."
Question: Is there a difference in the amount of mercury that a loon takes in while living in its northern range (i.e. Minnesota) versus its winter range?
Evers: "We have very little data on mercury uptake in wintering areas. Uptake in Minnesota can vary depending on the lake chemistry. Lakes in Northeast Minnesota have high mercury."
Question: How wide-spread is mercury pollution?
Evers: "Substantial mercury pollution of lakes and streams already exists on our continent. Global mercury levels are now 3-4x higher than natural background conditions. Recently, studies have found elevated levels of methylmercury in the body burden of loons. Although average whole blood mercury concentrations for Minnesota & Wisconsin loons are not as high as those found in New England and the Canadian Maritimes, they are double Alaskan samples that represent background levels. These blood studies show that loons are exposed to too much mercury."
Question: Does the mercury in lakes ever "go away?" Can it "settle out" to the bottom of lakes and lie undisturbed, or must it forever be part of the food chain, ending up in fish and loons?
Evers: "Mercury can settle out into bottom sediments and become less available to the food chain. In contrast, if lakes become acidic, mercury that's in the bottom sediments can actually be dissolved into the water."
Question: What methods are available to remove mercury from lakes?
Evers: There are no current methods used on lakes.
Question: How do you study mercury levels in loons?
Julie BrophyEvers: "We take samples of the feathers and blood. These samples show how much mercury is stored in their bodies. As more samples are collected we hope to have a clearer picture of how mercury and the loons' health are related. For example:
Julie BrophyAs shown in this picture, we collect the second, secondary feather. Previous studies indicate that feathers serve as the primary excretory pathway for organic mercury. Up to 93% of the body burden of mercury is deposited in feathers. Feathers are useful because:
Blood samples are more likely than feathers to give a recent history of mercury uptake. This is because mercury binds to red blood cells, and these red blood cells have a life span of about 3 months.
Question: Why is this research important for human health?
Evers: "Since loons are so high up in the food chain they may also be a very good indicator of how mercury could affect us. Many federal agencies and states use the loon as an "indicator" or benchmark of aquatic system health. Mercury studies have shown that the metal "bioaccumuates".
"Common Loons are ideal "early warning" indicators for human health, because we can study individual birds over the long-term. This is because loons (1) can be easily captured and recaptured, (2) are easy to monitor throughout the day, (3) show fidelity to a breeding territory, (4) are long-lived, possibly up to 30-35 years and (5) are highly sensitive to the bioaccumulation of methylmercury (10% each year).
"Since it's estimated that 95% of human mercury exposure is from eating fish, these long-them studies are important to humans. In fact, human consumption of fish is not recommended on many lakes due to mercury pollution. In the state of Minnesota for example, 1/3 of the state's 10,000 lakes have mercury advisories, cautioning people not too eat too many fish from those lakes."
How to Respond to Journey North Loon Challenge Question # 5
Challenge Question # 5
The Next Loon Migration Update Will be Posted on April 10, 1997.