-4- 
     
    
   
   
    
     A very interesting feature of the report was the number of species that 
     
     must have overslept, or failed to heed the migration urge! Who would 
     
     expect to encounter, just before Christmas, such birds as: Pintail 
     
     Duck, Myrtle Warbler, White-throated Sparrow, Song Sparrow or American‘ 
     
     Goldfinch? 
     
    
   
   
    
     Bruce McLaren 
     
    
   
   
    
       
     
    
   
   
    
     EVENING GROSBEAK BEHAVIOR AT FEEDERS 
     
    
   
   
    
     At the last meeting of the Natural History Soceity, a brief disucssion 
     
     on Evening Grosbeaks at feeders was brought up. It was noted that there 
     
     existed an unequal sex ratio and a few ideas were brought up on what 
     
     factors caused this phenomenon. Coincidentally, one day later, the 
     
     Autumn 1976 issue of Bird Banding, a journal published by the North- 
     
     eastern Bird Banding Association arrived. While thumbing through it, I 
     
     noticed an article entitled "Some factors influencing observed sex 
     
    
   
   
    
     ratios in a population of Evening Grosbeaks" by M.H. Balph and D.F. 
     
     Balph. 
     
    
   
   
    
     The authors studied grosbeaks in Logan, Utah, during late winter and 
     
     spring of 1976. Most of their data, however, dealt with the period 
     
     between mid-April to mid-May. Observations of sex-ratios were made in 
     
     four situations: (a) crowns of vegetation, (b) during trapping and 
     
     banding operations, (c) at a large elevated tray, and (d) a small 
     
     elevated tray (both trays were provisioned with sunflower seeds). The 
     
     number of grosbeaks present in the area during the study period was 
     
     estimated to be between 700 and 800 birds. 
     
    
   
   
    
     The sex ratio of females to males at different observation spots 
     
     varied. Females predominated at the first three situations listed a— 
     
     bove and males predominated at the small food trays. 
     
    
   
   
    
     The authors suggest several factors which could influence the sex 
     
     ratios observed within the 200 square meter study area. Differential 
     
     mortality as a result of conspicuousness of males could account for a 
     
     higher number of females. This, however, could be countered by dif- 
     
     ferential mortality as a result of social status (i.e., females, being 
     
     subordinate in this species, may be at a disadvantage if food resources 
     
     were limited). Differential migration patterns were also suggested 
     
    

    
     as a reason for unequal sex ratios and banding records suggested that 
     
     females may winter further south than males. 
     
    
   
   
    
     The marked difference in the ratio of birds around the small feeding 
     
     tray was attributed to grosbeaks social behavior. Males readily 
     
     attacked females and forced them away from the feeding station. Hence, 
     
     as the size of the feeding station decreases, there is a greater pro- 
     
     bability of having more males than females in the area because aggres— 
     
     sive tendencies of the males would increase at a limited food source. 
     
    
   
   
    
     It was interesting to note that many of the factors mentioned in the 
     
     article were considered or implied during the brief discussion at the 
     
     annual meeting. The above reference is in Volume 47 of Bird Banding 
     
     pages 340-344. I'll bring a copy to the next meeting for anyone who 
     
     would like to find out more about factors influencing grosbeaks at 
     
     feeders. 
     
    
   
   
    
     Earle Hickey Jr. 
     
     231 Grafton Street 
     
     Charlottetown, P.E.I.