ART. 18 PARASITIC HABIT IN DUCKS rRIEDMANN 7 



the water, and from then on any place is home to them. Hence the 

 territory lasts only as long as the incubation activities of the parents. 

 Thus it seems that the cause of the diminution of the potency of 

 territorialism is dependent on the lessening of the incubation activi- 

 ties. Inasmuch as the lessening of incubation is merely a step in the 

 path toward a complete lack of incubation, such as in the case of 

 those eggs laid in strange nests (that is, lack of incubation on the 

 part of the bird that laid the eggs), it follows that as this diminishes, 

 approaching zero as a limit, so too the territory as such becomes less 

 and less real and finally vanishes. In an analysis of the cyclical 

 instincts of birds during the reproductive period, the nest is merely 

 something constructed within a territory for the purpose of being a 

 receptacle for the eggs that are to come. Therefore, with the dis- 

 appearance of the territory as such, there must inevitably come about 

 a loss of the nest-building instinct. It is impossible to construct 

 something in a nonexistent space. Hence it follows that the loss of 

 the nest-building instinct is also dependent on the decrease in the 

 amount of incubation given the eggs by the female parents. Further- 

 more, to carry this idea a little further, it appears that the origin of 

 the parasitic habit in the Anatidae is bound up with the heat 

 adaptability of the eggs of the ruddy and black-headed ducks. If 

 their eggs did not have this peculiarity, any lessening of incubation 

 would have resulted in the extermination of the species; the fact 

 (?) that they have, has allowed for the development of parasitism 

 in this group of birds. 



v. S. •OVi;rNIIENT PBINTIHS office: 1992 



