SECT. XVI. 13. O F I N S T I N C T. 199 



2. They are fubjeft in their migrations to the 

 fame accidents and difficulties, that mankind are 

 fubjecl: to in navigation. 



3. The fame fpecies of birds migrate from fome 

 countries, and are refident in others. 



From all thefe circumftances it appears that the 

 migrations of birds are not produced by a necef- 

 fary inftincl:, but are accidental improvements, like 

 the arts among mankind, taught by their cotempo- 

 raries, or delivered by tradition from one genera- 

 tion of them to another. 



XIII. In the feafon of the year which fupplies 

 the nourimment proper for the expected brood, the 

 birds enter into a contract of marriage, and with 

 joint labour conftruct a bed for the reception of 

 their offspring. Their choice of the proper feafon, 

 their contracts of marriage, and the regularity 

 with which they conftrudt their nefts, have in all 

 ages excited the admiration of naturalifts ; and 

 have always been attributed to the power of in- 

 fHnft, which, like the occult qualities of the an- 

 tient philofophers, prevented all further enquiry. 

 We (hall confider them in their order. 



Their Choice of the Seafon. 



Our domeftic birds, that are plentifully fupplied 

 throughout the year with their adapted food, and 

 are covered with houfes from the inrlemeacy of the 

 weather, lay their eggs at any feafon: which evinces 

 that the fpring of the year is not pointed out to 

 them by a necelfary inftincl. 



Whilft the wild tribes of birds choofe this time 

 of the year from their acquired knowledge, that 

 the mild temperature of the air is more convenient 

 for hatching their eggs, and is foon likely to fupply 



. that 



