First, shall it be the male's or the female's weight? This 

 is decidedly important, for there is a great difference in the 

 weights of the two sexes with many birds — it may be 20% 

 in the ostrich, and the male prairie falcon's weight is but 

 33 1-3% as much as its mate; and the female European 

 sparrow hawk (Accipiter nisus) is said to weigh, at times, 

 twice as much as its mate (181). Secondly, it is necessary 

 to take a season which may possibly have the greatest in- 

 fluence, if any, over the length of incubation, i. e., the breed- 

 ing season, for it will probably be found that a bird's weight 

 follows most closely a normal at this time of the bird's 

 physiological year, and hence be less fluctuating and more 

 influential. 



If now one tries to study a comparison between birds' 

 weights and the duration of their incubation periods, there 

 arises at once an awkward obstacle, namely, a ridiculous 

 paucity of data on bird weights. The following list gives 

 all the records of bird weights which have come to light in 

 the prosecution of this study, plus those determined by the 

 writer. 



TABLE NO. 3 



Weights of Birds in Ounces Aiwirdupois 



Weight Authority- 

 Ostrich $ avg. 4000.00 141 



Kiwi 64.00 42 



" 60.00 168 



Emperor Penguin 1440.00 20 



Adelie Penguin 42.50 20 



Albatross 224-288.00 185 



Yellow-billed Tropic Bird 14.00 26 



Pelican (Pelicanus mitratus) 512.00 181 



White Pelican $ , Juv. October 240.00 78 



Great Blue Heron 96-128 180 



Heron (Ardea cinerea) 64.00 181 



Wood Ibis 144-192 180 



Domestic Duck (Eouen) 9 128.00 34 



Shoveller Duck— $ —May 11 17.25 78 



Grey Wild Geese 9 160.00 34 



Greater Snow Goose 80-104.00 180 



Canada Goose 128-224.00 180 



Brant 64.00 180 



Whistling Swan 192-304 180 



California Vulture avg. 320.00 100 



Gyrfalcon (Falco rusticola gyrfalco) 84.00 180 



Prairie Falcon 9 72.00 145 



" " $ Dec. 3 22.30 78 



" " $ 24.00 145 



Western Sparrow Hawk 9 July 4.76 78 



21 



