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.