GULL EXCLOSURES INSTALLED by San McAskiT‘ 
     
    
   
   
    
     On Aprii 22nd and 23rd, voTunteers 
     
     of the NaturaT History Society of Prince 
     
    
   
   
    
     Edward Isiand Toaded heavy cod Tine, 2 x cw W“ 
     
     45, metai strapping, and tooTs in a k{”/’ 
     
    

    
     Boston whaTer and a Zodiac raft so that _._- .. -_— - 
     
    

    
     guTT echosures coqu be instaTTed on __ __ ___.. 
     
    
   
   
    
     four of the Hiiisborough Bridge Piers. 
     
     The two boats were used in conjunction 
     
     with up to four cTimbers to instaiT the 
     
     monofiiament Tines in a manner simiiar 
     
     to the guii exciosures deveToped by Hans 
     
     Biockpoei of the Canadian WdeTife 
     
     Service in Ontario. The exciosures 
     
     consist of paraTTeT heavy monofiiament Tines stretched between upright poTes. 
     
     These Tines discourage guTTs from landing because they tend to Tand in a 
     
     sweeping gTide whereas terns settTe sTowTy from a hovering position. 
     
    

    
     This work is a continuation of over 20 years of monitoring the Common 
     
     Terns nesting on the on bridge piers (refer to IsTand Naturaiist Issue 111 for 
     
     the history of this coTony). This monitoring has shown that the Great 
     
     Biack-backed GuTTs, a single pair of which started nesting on the site in 1985, 
     
     are causing a serious decTine in the terns using this site and have reduced the 
     
     production of tern young to very Tow numbers. This spring there were four pairs 
     
     of Great Biack-backed Guiis occupying four piers and experience has shown that 
     
     the guTTs wiTT eat either the eggs or the young of the terns nesting on the 
     
     same pier as weTT as adjacent piers. 
     
    

    
     In 1988, the Society had two summer students monitor the guTT and tern 
     
     interactions at the on bridge piers and, since then, the Society has gathered 
     
     scientific information on these interactions from throughout eastern Canada and 
     
     New Engiand. In AtTantic Canada, decTines and abandonments of tern coTonies 
     
     have been frequent in the past few decades. An estimated 44,000 pairs of Common 
     
     and Arctic terns stiTT nest in Atiantic Canada but this is a substantiaT 
     
     reduction from tern numbers at the turn of the century when 100,000 to 500,000 
     
     pairs nested on Sabie Island aione. Tern numbers in the Great Lakes have 
     
     decreased from 16,000 pairs to 3,000 pairs in the past 20 years. Monitoring in 
     
     New EngTand has shown that once terns abandon a nesting site, it is difficuit 
     
     to encourage their'return. Research over the past 30 pTus years indicates that 
     
     action shouid be taken before terns abandon a nesting site. 
     
    

    
     Great BTack-backed Guiis and Herring Guiis popuTations have increased 
     
     dramaticaiiy in response to garbage, human waste, and fish waste handiing 
     
     practices. There are heaTthy breeding coionies of both species in HiiisborOugh 
     
     Bay and the movement of the 4 pairs of birds away from the HiTstorough piers 
     
     wiTT have a negligibie impact on their popuiation. 
     
    

    
     The Society wiTT'be monitoring the site throughout the breeding season to 
     
     determine how the terns and guiis respond to the exciosures. The Society hopes 
     
     that this non-destructive technique wiii be sufficient to protect the terns 
     
     nesting at this site. The work was carried out in conjunction with the advice 
     
     and permission of the Canadian NdeTife Service. 
     
    

    
     Thanks to Bruce Smith, AT McLennan, PhiT Hard, Geraid MacDougaTi, Ted 
     
    

    
     Currie, Robert Redmond, Todd Dupuis, and Bruce Pigot who voiunteered their 
     
    

    
     time and expertise to assist with the cTimbing and/0r pTanning for this 
     
    

    
     project. Thanks aTso to Hans Biockpoei and Tony Locke of the Canadian 
     
    

    
     WdeTife Service who provided vaTuabTe advice on the echosures. 
     
    
   
   
    
       
     
    
   
   
    
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