HILLSBOROUGH BRIDGE PIER TERN COLONY by Pam MacEachern 
     
    
   
   
    
     The Hillsborough Bridge was constructed between 1901 - 1903 primarily for 
     
     rail transport. The bridge extended 4,496 ft. in length from "The Old 
     
     Shipyards Point" on the Charlottetown side to "Mutches Point" on the Southport 
     
     side. The piers were numbered 0 to 11 from Charlottetown to Southport 
     
     (Anonymous, 1900) and that numbering system is still used. The steel section 
     
     of the bridge was removed after the new bridge was opened in 1963. The steel 
     
     span was successfully removed but efforts to move one of the stone piers 
     
     resulted in its collapse. The Natural History Society of Prince Edward Island 
     
     lobbied for the retention of the remaining piers as a nesting site for the 
     
     terns which were already using the north and south ends on the bridge (Bruce 
     
     Pigot, Pers. Comm.). A letter to Mr. Bruce Pigot from J.E.V. Goodwill dated 
     
     October 6th, 1965 indicated that terns were nesting on the rock filled crib to 
     
     the north-east side of the swing section of the Hillsborough Bridge on July 
     
     3rd, 1948. He counted 50 adults and 8 young on that date. In 1965, Bruce Pigot 
     
     noted that "In addition to the north and south colonies, terns are now nesting 
     
     on the piers of the old Hillsborough Bridge. Twenty-four adults were flushed 
     
     off these. They very likely are nesting" (The North and South colonies refer to 
     
     the pentagon shaped rock piers adjacent to the swinging portion of the bridge). 
     
    

    
     The discarded piers had become home to 
     
     a colony of Common Terns. Margaret Mallett 
     
     kept records of the number of birds in the 
     
     colony from 1972 to 1976. In 1984 a pair of 
     
     Great Black-backed Gulls established a nest 
     
     on pier # 10 and some members of the Natural 
     
     History Society of Prince Edward Island 
     
     became concerned for the tern colony 
     
     at this site.' That pair was successful in 
     
     rearing young and a pair was successful in 
     
     rearing young on that pier each year from 
     
     1984 to 1988. In 1987 Great Black- 
     
     backed Gulls also established a nest on pier # 7 and a pair occupied pier # 6. 
     
    

    
     Bruce Pigot recorded the early dates of occurrence for Common Terns as May 
     
     22 to June 3 over an eleven year period ending in 1967. E. Holdway recorded the 
     
     early dates of arrival of the terns at Wood Islands between May 16th and May 
     
     22nd during the 10 year period 1956 to 1965 (Pers. Comm. to B. Pigot from E. 
     
     Holdway). Dan McAskill (pers. comm.) recorded the dates that he first observed 
     
     terns on the Hillsborough Bridge Piers in four of the last five years. These 
     
     were: May lst in 1984; May 3rd in 1985; May 5th in 1987; and May 6th in 1988. 
     
     The date for 1986 was not recorded. He noted that the Great Black-backed Gulls 
     
     occupied their nests several weeks before the terns returned. Bruce Pigot 
     
     estimated the total population of Common Tern in Prince Edward Island in 1966 
     
     to be 2,874 based on the number of occupied nests in 32 colonies. He noted the 
     
     probable displacement of Common Tern colonies from the Pownal Islands by the 
     
     Great Black-backed Gulls. 
     
    

    
     The objective of this study was to ascertain whether or not the presence 
     
     of the Great Black—backed Gulls on the Hillsborough Bridge Piers was having a 
     
     negative impact on the number of Common Tern utilizing the piers or on the 
     
     number of young being produced from this colony. This concern was raised by 
     
     two Natural History Society members concerned over reported declines in the 
     
     tern population in the region (Dan McAskill, pers. comm.). 
     
    
   
   
    
       
     
    
   
   
    
     Common Tern