In 1993, the Ontario Ministry of Natural Resources (OMNR) and the Canadian Cooperative Wildlife Health Centre (CCWHC) began an investigation of disease and mortality of Common Loons in Ontario. The principal objectives were to document causes of mortality in adult loons, exposure of loons to lead and mercury, and to describe incidental disease conditions such as parasites. A request was made to all OMNR field staff to retrieve and submit as many loon carcasses as possible. The Canadian Lakes Loon Survey was also made aware of the study, as were wildlife rehabilitation centres. In 1994, the CCWHC was contacted by Tony Scheuhammer of the Canadian Wildlife Service, who was in the midst of a study of the toxicology of metals in loons, and was looking for tissues in order to measure lead, mercury and selenium levels. A collaborative effort was begun in which the CCWHC provided samples from all of the loons it received, and CWS conducted lead and mercury analyses on these tissues.
Since 1993, 62 adult loons (many of them submitted by CLLS volunteers) have been examined. In addition, necropsy reports were completed for 9 birds previously submitted to the Ontario Veterinary College. A protocol has been developed for the examination of each carcass. The location where the loon was found, and the circumstances surrounding its death are recorded. The birds are first measured and weighed. A standard necropsy is conducted, in which all body systems are examined in a search for significant abnormalities or evidence of disease processes. Samples of liver, kidney, brain, pectoral muscle and a wing are sent to the CWS for toxicological testing. In most instances, samples of a wide range of tissues are collected for histological examination. Any parasites noted are saved for identification. From the gross examination of the carcass, microscopic examination of tissues, bacteriological culture and toxicological measurements, it is usually possible to determine cause of death.
The major causes of death in the Common Loons examined are given below:
Cause of Death |
Number of Birds |
% of Total |
|---|---|---|
27 |
38.0 |
|
19 |
26.8 |
|
6 |
8.5 |
|
5 |
7.0 |
|
2 |
2.8 |
|
6 |
8.5 |
|
Unknown |
6 |
8.5 |
Total |
71 |
100.0 |
"Trauma" is the most important cause of death, accounting for 27 of 71 deaths. Seven individuals were shot; 9 died of injuries due to collisions with boats, cars or power lines; 6 died of drowning in fishing nets, and in 5 cases the source of the trauma was not determined.
Lead poisoning was the next most common cause of death. The source of lead was usually obvious; in 15 of 19 birds a fishing weight was present in the gizzard. Fishing weights of many kinds were found, but jig weights were the most common. Tissue levels of lead were very high in some of these birds. In waterfowl, tissue levels in excess of 20 parts per million (ppm) is taken to be evidence of lead poisoning. In these loons, liver levels ranged as high as 270 ppm and kidney levels were as high as 480 ppm. There was no evidence of subclinical lead poisoning as is sometimes seen in waterfowl, indicating that when loons ingest lead, it is usually in sufficient quantity to be fatal.
Aspergillosis is a fungal infection that occurs in many species of birds, usually affecting lungs and air sacs. It is an organism that is widespread in the environment, and it is believed that most birds are resistant to its infection, unless they are weakened by some other disease, injury or stress. All but one of the six loons dying of aspergillosis had some other serious disease condition as well.
In five birds, the cause of death was attributed to the effects of having fishing line tangled around the bill, or of having swallowed a fish hook which subsequently became embedded in the digestive tract. In either case, the birds were unable to eat, and these loons died of starvation.
Two birds died due to the effects of extremely high burdens of intestinal parasites. Other birds were found to have substantial parasite burdens too, but also had more serious conditions which likely caused their deaths.
Six birds died of a variety of unusual conditions such as rupture of a major blood vessel or impaction of the oviduct with eggs and subsequent rupture and release of eggs into the abdomen. In another six birds, no cause of death was determined.
One of the more obvious implications of these findings is the importance of human activities in causing the deaths of adult loons during the nesting season. At least 51 of 71 birds (72%) died as the result of trauma, entanglement or lead poisoning, all of which are consequences of human actions.
While these deaths may be representative of mortality during the nesting season, this may be a period when relatively few deaths occur compared with migration and over-wintering. Commercial fishing nets likely claim a significant number of birds during migration and on the wintering grounds. Obviously, data collected over a longer term from a wider geographical area will be required in order to develop a more complete picture of the major causes of mortality in loons in Canada.
- Doug Campbell
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Canadian Lakes Loon Survey
Bird Studies Canada
P.O. Box 160
Port Rowan, Ontario
Canada N0E 1M0
Tel: 519-586-3531 Fax: 519-586-3532
Questions about the CLLS? Please contact Kathy
Jones
Email:
aqsurvey@bsc-eoc.org