only 20 adult Common Terns. The terns stayed on that pier until July 7th and 
     
     attempted to rear young as did the gulls. The sightings on July 14th showed 
     
     only the presence of the Gulls and it remained that way for the rest of the 
     
     study. The Common Tern is very protective of its young and will display 
     
     aggressive behavior toward any object it considers a predator. The gulls which 
     
     did occupy the same nesting site as the terns were observed being harassed by 
     
     the terns quite often. This type of behavior takes the tern away from its 
     
     nesting and feeding activities which could cause a reduced fledging success 
     
     rate. The number of chicks noted on pier #7 appeared to drop to 50% over this 
     
     time period. Actual predation by the gulls was not seen by the author but was 
     
     reported by others. The number of the terns using the colony showed a steady 
     
     decrease from 228 adult terns on June 17th to 96 adult terns on July 28th. 
     
    

    
     Dan McAskill (pers. comm.) reported the presence of at least 6 pairs of 
     
     Common Terns exhibiting nesting behavior on Pier # 10 in late May. By the time 
     
     observations were started in this study those terns had abandoned any attempt 
     
     to nest on this pier although terns were often observed harassing the adult 
     
     Great Black-backed Gulls and young on this pier during the period of the study. 
     
     0n the remaining piers, the terns and gulls did not occupy the same pier and, 
     
     while the adult terns did spend time harassing the Great Black-backed Gulls on 
     
     the piers on which the gulls were nesting, on the light standards, and on the 
     
     service road, the gulls were not seen landing on these other piers. 
     
    

    
     While the tern and gull chicks were difficult to see as they tended to 
     
     settle in the lower or grassy areas of the piers a comparison between the tern 
     
     piers with and without gulls present suggests greater nesting and hatching 
     
     activity on piers without Great Black-backed Gulls. 
     
    

    
     Double—crested Cormorants were located on pier #3 throughout the study. 
     
     1988 was the first year that cormorants remained on the piers throughout the 
     
     tern breeding season. A pair of adult Great Black-backed Gulls was observed 
     
     rearing young on that same pier. The Double-crested Cormorant's interaction 
     
     with the Common Terns was restricted to competition for space on the piers and, 
     
     possibly, competition for food. 
     
    

    
     Based on the observations made during this study there appears to be a 
     
     link between the tern and gull populations in this colony. Not only do they 
     
     compete for food, they also compete for nesting space and the terns must 
     
     prevent the gull from predating its nests and young which, if they remain in 
     
     the same breeding area, will continue to create a problem for the tern 
     
     population. 
     
    
   
   
    
     (Editor's Note: 
     
    

    
     1. This article was excerpted from the Natural History Society of Prince 
     
     Edward Island's 1988 SEEDS Project Report. This project was implemented by 
     
     Pamela MacEachern and Shelley Barrett who were employed by the Society with 
     
     funds provided by the Canada Employment and Immigration Commission and the 
     
     Prince Edward Island Conservation Strategy. 
     
    

    
     2. Wildlife managers must base decisions to intervene in species management 
     
     on p0pulation data and a judgement of need. In the case of endangered species 
     
     such as the Whooping Crane, there has been strong support for this 
     
     intervention. A recent decision to intervene on behalf of the terns on Sable 
     
     Island was withdrawn due to public opposition over the proposed gull kill. The 
     
     situation in the Hillsborough Tern Colony raises a similar controversy. Should 
     
     the Great Black-backed Gulls on these piers be removed or prevented from 
     
     nesting on the piers so that the Common Terns will face less predation and so 
     
     they can reoccupy their former nesting territory? What do you think? I will 
     
     explore this matter further in a future issue. J.D.M.) 
     
    
   
   
    
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