In spite of their popularity, we know relatively little about the life history of Common Loons. Even basic questions, such as their age at first breeding, mortality between fledging and first breeding, life span, fidelity to mates and breeding territories, migratory routes, and the relationship between the breeding and wintering areas of specific populations are largely unknown or based on speculation derived from limited data. Banding Common Loons to identify individuals is helping to answer many of these key questions.
The capture of loons for banding also allows blood and feather samples to be taken for analysis of mercury and other contaminants. Mercury enters the environment from industrial sources such as chlor-alkali plants and wood pulp plants, and as a result of energy production and the disposal of consumer products. Inorganic mercury is taken in and methylated by microorganisms. In this form it is easily taken up by aquatic insects and invertebrates and then concentrated at each successive level of the food chain (a process known as biomagnification). High-trophic-level predators such as Common Loons are therefore especially vulnerable to the effects of mercury.
Jack Barr, a noted loon researcher, reported lowered breeding success of Common Loons when mercury concentrations in their prey averaged greater than or equal to 0.3 micrograms per gram wet weight (wg/g). Other researchers have since found that up to 30% of Ontario lakes sampled contained small fish (the size eaten by adult loons) with mercury concentrations greater than levels that Barr linked to reduced breeding success in loons.
Concerns about the effects of mercury and other contaminants on loons were the impetus for two separate loon banding studies in Canada. In 1992, the Canadian Wildlife Service, Dave Evers (an independent biologist) and the Canadian Lakes Loon Survey (CLLS) banded 24 adult and 36 juvenile loons on 23 lakes in central Ontario. In 1995, we banded 17 adults and 11 juvenile loons in Nova Scotia and New Brunswick. Blood and feather samples were taken from most of these birds when they were banded. In addition to numbered metal bands, we placed coloured bands on their legs, so that individual loons could be identified in subsequent years without recapturing them.
Loons captured in Kejimkujik National Park, Nova Scotia in 1995 had the highest levels of mercury and the lowest reproductive success of loons anywhere in North America. This finding prompted continuation of the study to capture, band and blood-sample loons in Atlantic Canada to determine the impacts of mercury on loons.
In 1996, the loon capture team netted a total of 23 birds (14 adults and 9 chicks) and collected blood samples from birds on 13 new territories. Loon capture is done with special dip nets at night, but is still not an exact science. This year, loons in Nova Scotia and New Brunswick hatched on average two weeks earlier than last year, which meant that most chicks were more than four weeks old when the team was in the field. At this age, both adults rarely attend the young at night, so we were unable to catch both pair members on any new lakes this year. However, with repeated visits we were able to secure at least one adult from most of the lakes visited. We also managed to recapture and take blood from two adults sampled in 1995, to measure year-to-year variation in blood mercury levels.
Banded loons need to be resighted if we are to study the effects of mercury on the survival of loons over time or answer many of our other questions about loons. In 1996, Loon Survey volunteers reported on the status of several loons banded in Ontario in 1992 (many thanks to Pam Hickman, Robert Stevens and Ruth and Vic Orr). CLLS staff supplemented these observations by checking 17 central Ontario lakes on which Common Loons were colour-banded in 1992. If banded loons were not found on these lakes, we checked adjacent lakes or adjacent territories on multi-pair lakes, as time allowed, to determine whether absence of the loons represented mortality or dispersal to neighbouring territories. Surveys at other locations in North America have shown that some adult loons will move up to 7 km. to a new lake, although they rarely go farther than adjacent territories.
In Ontario, volunteers and Survey staff together located 11 of 24 adults loons, four years after they were colour-banded in 1992. Ten of these loons were found on the same territories on which they were originally banded. In Nova Scotia and New Brunswick, all adult loons banded in 1995 were relocated on their breeding lakes. These results reinforce the premise that adult loons are very site-faithful and return to "their" lakes year after year. Moreover, in at least one instance, we found both members of a banded pair together on their lake -- evidence that at least some loons are faithful to mates over the years.
We did not find any loons colour-banded as juveniles. Young loons stay on the ocean, however, for several years after they fledge, before returning to freshwater lakes to breed -- four years may be too early to expect them. Also, they may be less likely than adults to return to the same lakes where they were banded. (For one thing, they might have to battle with their own parents for possession of the territory!)
Studying the survival and dispersal of either the young birds or those adults that may not have returned to their original lakes, is not an easy task, and clearly not possible for a single field crew. Likewise, while loons banded as juveniles may return to the same general areas as their birthplace, the likelihood of a loon settling on the exact lake on which it was born is small. Watching large areas for returning adults and young can only be achieved through the committed efforts of our large base of volunteers.
Blood and feather samples were taken from Ontario loons when they were banded. Mercury concentrations in blood are thought to be a good indicator of mercury concentrations in prey species in breeding lakes. Mercury concentrations in feathers are also influenced by mercury concentrations in wintering areas at the time of moult and feather formation. Blood mercury levels in Ontario loons averaged 2.1 ug/g.
Perhaps somewhat surprisingly, we found no evidence that these levels of mercury affected survival of the adult loons. All of the loons banded in the Maritimes in 1995 returned in 1996, regardless of their mercury levels. In Ontario, there were no significant differences in blood or feather mercury concentrations between banded loons that had disappeared and those that were subsequently resighted four years later. These findings, although based on a small sample size, suggest that mercury at the concentrations we are observing does not markedly affect year to year survival and/or territorial fidelity of loons.
Nevertheless, mercury and other compounds may well have effects on reproductive rates or have more subtle effects on the health or well-being of the loons. Ongoing monitoring and observations, such as those by participants in the CLLS, can help us to monitor these effects. Studies such as the current banding activities can also help to identify areas of potentially dangerous concentrations of mercury, an important first step in reducing mercury in our environment to the benefit of loons and other animals, including people.
The large network of CLLS volunteer surveyors watching loons increased the chances of banded adult and juvenile loons being sighted and reported. Looking for colour bands demands a high level of commitment from volunteers; the bands are approximately 27 mm long and 17 mm wide, and are most easily seen by patiently watching a bird with a spotting scope, until it happens to roll on its side to preen or "waggle" its foot, thus exposing the band. Nevertheless, several volunteers have met the challenge and provided us with invaluable information. Please keep watching!
If you find a banded loon, make sure you note the colours of the bands and which leg each was on (loons are colour banded on both legs). Then write us with the information. We will provide you with information about the history of the loon you sighted.
- Harry Vogel
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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