COMMON LOON STATUS

BY MARTIN K. MCNICHOLL . CHAIRMAN, ICBP—CANADA

The Common Loon or Great Northern Diver (Gavia immer) is a wide- spread, primarily boreal-nesting species of North America. The relative remoteness and inaccessability of much of its breeding range might be expected to afford it protection from significant disturbance, but de- clines in New England and some other U.S. states have been sufficiently steep to cause one group of scientists to request that the U.S. govern- ment and a number of specific states conduct a review to consider assign- ing it endangered or threatened status. In 1980, the Common Loon was added to the "blue list" of North American species showing non-cyclical declines in at least part of their breeding range. In 1982, the "blue list" was altered to separate species showing evidence of widespread decline from those with local problems and those "of special concern," because of vulnerability to some environmental feature or contaminant. The Common Loon was assigned to the special concern category because of its susceptibility to loss of nests in the wakes of boats and problems posed by acid rain.

The habit of loons of nesting close to the edge of the water makes them naturally susceptible to nest loss by flooding, but this natural hazard can be greatly magnified by artificial aterations in water levels and/or considerable use of a water body by motorized boats. Mere intrusion of humans into the vicinity of nests and to a lesser extent of chicks can pose a nesting hazard, although habituation may partially offset this hazard in some areas. Egg predation on loons by increasing populations . of coons and skunks in New England is thought to be a factor in declines

f loons there and bears watching in areas of Canada where these species are undergoing range expansions. All of these nesting hazards may be quite localized, but as predators at the top of the aquatic "food chain", loons are vulnerable over wide areas to chemical contaminants, both di- rectly by mercury or pesticides and indirectly through dimunition of food supply through acid precipitation. In addition to these hazards as- sociated primarily with nesting areas, loons are susceptible in both nesting areas and winter/migration sites to outbreaks of botulism and aspergillosis, occasionally in epidemic proportions. Entanglement in fishing nets can also be a serious problem in lakes or seas that support commercial fishing and like all water birds, loons can be harmed by oil pollution.

Populations of Common Loons in Canada are poorly documented, and would be very difficult to determine. Nest records in B.C. indicate that they may be less common and less widespread as a breeding species than generally believed. The atlas projects now underway in several provinces should help define its exact breeding range, but will not provide a pop- ulation estimate. Breeding Bird Survey results suggest some fluctuation in numbers in those areas close enough to roads to be surveyed, but the results of this type of survey may not be very instructive on widespread trends for this species.The Ontario Lakes Loon Survey of the Long Point Bird Observatory will hopefully indicate trends in Ontario, as product— ivity is compared for particular lakes from year to year. This survey wa initially designed to compare productivity on acidified lakes with that of non—acidified lakes, but is now being expanded to consider other factors also.