ON THE SUBJECT OF 
     
     CORMORANTS 
     
    
   
   
    
     by Geoff Hogan, Springvale, P E.I. 
     
    
   
   
    
     Anyone birdwatching along the shore this 
     
     fall or just driving across the Hillsborough 
     
     Bridge or near the Summerside waterfront will likely 
     
     have noticed the presence of cormorants. It is the 
     
     time of year when cormorants are dispersing from the 
     
     summer breeding colonies and, in the case of the Double- 
     
     crested CormOrant (Phalacrocorax auritus), preparing for 
     
     migration south. You will also likely have noticed that 
     
     there are more cormorants than you remember before. The 
     
     reason is, of course, that in the past few years cormorants on P E.I. have under- 
     
     gone a substantial population increase. Whereas the last thorough census in 1978 
     
     revealed six colonies on the Island, by 1983 there were eleven. Interestingly, 
     
    

    
     a similar increase in cormorants has been occurring elsewhere such as the Great 
     
     Lakes (C. Weseloh, pers. comm.). Both of our species, the Great (3, carbo) and 
     
     Double-crested cormorants, have shown a population increase. 
     
    

    
     There are several possible factors that may explain this increase, although 
     
     it is difficult to say with certainty which factor is most important. Earlier 
     
     in this century cormorants were widely persecuted along the east coast (and else- 
     
     where) to such an extent that Double-crested Cormorants were extirpated along the 
     
     coast of Maine and New England as a breeding species and Great Cormorants were 
     
     thought to have been completely extirpated as a breeding species in North America 
     
     (Bent 1922, Erskine 1972, Lewis 1929). However, both species returned to their 
     
     former range to nest and by mid-century appeared to have reached a peak. Pop— 
     
     ulation growth since then has been less rapid ... until recently. As a result, 
     
     the increase may simply be a delayed recovery to their original population level. 
     
     Another possibility may be that reproductive potential has improved since the 
     
     reduction of harmful pesticides (lg DDT) in our environment. Like many species 
     
     high on the food chain cormorants in some areas were adversely affected by such 
     
     pesticides. In addition, growing populations elsewhere may be adding new recruits 
     
     to our own population. Whatever the reason, cormorants evidently find P.E.I. to 
     
     their liking. 
     
    

    
     While both species of cormorants are seen most often on salt or brackish 
     
     water, Double-crested Cormorants will also visit freshwater ponds to feed. It 
     
     is the feeding habits of cormorants that is the subject of concern to fishermen 
     
     in particular. Cormorants feed upon a variety of fish and have been widely 
     
     persecuted for this reason. 0n the contrary, certain naturalists maintain that 
     
     cormorants keep fish stocks healthy by removing the weak and diseased and that 
     
     they are, in fact, beneficial because they feed upon certain fish species that 
     
     prey upon young lobsters. Birdwatchers enjoy cormorants for esthetic reasons 
     
     as P.E.I. offers some of the best opportunities to view nesting cormorants in 
     
     the Maritimes. 
     
    

    
     But what do they eat? There have been numerous studies to date on the 
     
     feeding habits of cormorants, often in response to fishermen's complaints that 
     
     the birds are a threat to the fishery (Lewis 1929, Madsen and Sparck 1950, Men- 
     
     dall 1936, Robertson 1974, Ross 1973, Scattergood 1950, Traverner 1915 and 
     
     others). All of these studies have shown the same result ....Cormorants rarely 
     
     prey upon economically important species and, except in unnatural situations 
     
    
   
   
    
     8