ABT. 18 PARASITIC HABIT IN DUCKS FRIEDMANN D 



lessness would only result in a form of check upon the increase of 

 the species population. The fact that the female ruddy ducks seem 

 to incubate but little after the first few days suggests that their eggs 

 may have a higher viability than most, or may be able to keep on 

 developing under rather adverse conditions. If this were so, then 

 the eggs laid at random in other birds' nests might well survive even 

 if only incubated a little now and then. It is therefore of pertinent 

 interest to find that such is definitely the case in the European ruddy 

 duck {Eris7natura leticocephala) . Henke " took some eggs of this 

 duck, and, after putting them in a bowl at room temperature, found 

 that they kept as warm as if they had been incubated. Not only was 

 slight cooling, such as room temperature, ineffective in harming 

 them, but extreme heat was likewise survived by the embryos. By 

 accident Henke left the eggs on a warm stove for some hours, and 

 then removed them, and after a week he was agi'eeably surprised to 

 see the eggs hatch. Apparently they were not injured by the stove 

 heat, but still the heat was probably considerably more than that of 

 ordinary incubation. This experiment, while crude and still un- 

 checked, serves to indicate the high degree of probability of ruddy 

 ducks' eggs surviving rather untoward conditions. 



Recently Meyer and Stresemann " have suggested that megapodes' 

 eggs and ruddy ducks' eggs hatch by virtue of the heat they retain or 

 generate themselves after the first few days of embryonic develop- 

 ment. The notion that the heat is supplied the megapodes' eggs by 

 the fermentation and decay of the vegetable matter in the mound is 

 thought to be questionable ; the mound may serve merely to prevent 

 the loss of heat from the eggs after the first few days, when the eggs 

 do actually receive heat from the mound or sun. As far as I know, 

 there is no positive evidence in favor of these eggs possessing any 

 mechanical or structural peculiarity in their thermal adjustments 

 not found in eggs of other birds, but the facts of their incubation 

 seem quite well founded. 



It seems, from the above, that in the ducks there is a tendency 

 to drop an occasional egg in another nest; this tendency becomes 

 more pronounced in some species, and reaches its climax in the ruddy 

 ducks and their near allies, and its very pinnacle in the parasitic 

 Heteronetta. With the growth of this tendency is correlated an 

 independent factor, namely, the heat-retaining, or perhaps heat- 

 generating, properties of the eggs. Thus it may be that the so- 

 called " dumping nests " of the redhead and canvasback, mentioned 

 by Bent, are extra nests of birds that have lost some of the single- 

 nest limitations and contain eggs that have been partially incubated 

 and that are left to their own heat resources. Wliether the eggs 



>»Zool. Garten, vol. 21, pp. 142-147. 1880. 

 " Orn. Monatsb., vol. 36, pp. 65-71, 1928. 



