- ERON , 
     
     CENSUS 
     
    
   
   
    
     THE 1981 GREAT BLUE HERON CENSUS 
     
     ' by Rosemary Curley, Fish and Wildlife Division 
     
    
   
   
    
       
     
    
   
   
    
     A thorough census of great blue herons in 1981 revealed some startling 
     
     statistics regarding Prince Edward Island's breeding population. Final results 
     
     will be presented by Al Smith, the Maritime Heron Census Co-ordinator, in a 
     
     comprehensive report in 1982, but on request of several interested heron censusers, 
     
     some preliminary data are presented here. All data are subject to interpretation, 
     
     and slightly different figures may be used later. Data for Rustico Island have 
     
     been kindly forwarded by P.E.I. National Park staff. 
     
    

    
     Natural History Society members and friends spent an estimated 75 man—hours 
     
     inside nine active colonies ranging in size from 20 to 380 nests (Table I), while 
     
     P.E.I. National Park staff censused the colony on Rustico Island. Four of five 
     
     colonies unused in 1980 were also rechecked, but their status remains unchanged 
     
     (Table II). 
     
    

    
     In total, 1715 active nests were recorded, far exceeding the approximately 
     
     900 nests counted during 1980 surveys. Mean colony size of 172 nests again 
     
     surpasses the estimated average of 75 nests calculated by Al Smith from pre-l980 
     
     datafi(Smith, 1980). It is possible that heron numbers have increased naturally 
     
     .since the mid—seventies when colonies on P.E.I. were surveyed by Geoff Hogan, 
     
     but expansions in actual colony size have probably resulted in part from an influx 
     
     of birds from several colonies now.deserted (Table II). The increase over 1980 
     
     estimates can be attributed largely to improved survey techniques, wherein 
     
     individual trees were marked with flagging tape to facilitate accurate nest counts. 
     
     ‘After the 1980 experience, censusers allowed adequate time to properly census 
     
     colonies, and the weather was more conducive to travel to offshore islands. More 
     
     colonies were well-censused in 1981 than in 1980. 
     
    

    
     An estimate of 100 nests on Governors Island in 1980 is now replaced by an 
     
     accurate count of 248 nests, 202 of which were active. Similarly, estimates for 
     
     Boughton, Herring and Glenfinnan Islands are replaced by counts exceeding the 
     
     1980 estimates by 50 to 100 nests. pn Oulton's Island censusers discovered an 
     
     additional part of the colony which was previously active, and expanded their 
     
     1980 count by approximately 100 nests - to 375! A first count of Courtin Island 
     
     by five enthusiasts indicated that approximately 380 nests were present, but 
     
     censusing the sprawling colony posed problems for the group, so this remains an 
     
     estimate. 
     
    

    
     A rough estimate of the peak population of great blue herons on P.E.I. is 
     
     now possible. If there are 1715 pairs (3430 adults) of great blue herons, each 
     
     successfully raising 2.4 young annually (4116 young), the Maritime average last 
     
     year, this adds up to a post-fledging population of 7546 herons. This does not 
     
     take into account numbers of non-breeding birds, or the possibility of adult 
     
     mortality. 
     
    

    
     The 1981 heron census people have achieved excellent results under often 
     
     difficult circumstances, and this data would not be available without their 
     
     perseverance and ready co—operation. Thanks to them, several points of curiosity 
     
     about great blue herons have been satisfied. An additional article on the Heron 
     
     Census will be presented in this newsletter in early 1982, with further information 
     
     on breeding success, including comparative results from New Brunswick and Nova 
     
     Scotia. 
     
    
   
   
    
     4