884 BIEDS OF PASSAGE. 



migrations on the waters of the Rio Negro. When the 

 Orinoco begins to swell* after the vernal equinox, an innu- 

 merable quantity of ducks (patos careteros) remove from 

 the eighth to the third degree of north latitude, to the first and 

 fourth degree of south latitude, towards the south-south-east. 

 These animals then abandon the valley of the Orinoco, no 

 doubt because the increasing depth of waters, and the inun- 

 dations of the shores, prevent them from catching fish, in- 

 sects, and aquatic worms. They are killed by thousands in 

 their passage across the Bio Negro. When they go towards 

 the equator they are very fat and savoury ; but in the month 

 of September, when the Orinoco decreases and returns into 

 its bed, the ducks, warned either by the voices of the most 

 experienced birds of passage, or by that internal feeling 

 tvhich, not knowing how to define, we call instinct, return 

 from the Amazon and the Rio Branco towards the north. 

 At this period they are too lean to tempt the appetite of the 

 Indians of the Rio Negro, and escape pursuit more easily from 

 being accompanied by a species of herons (gavanes) which 

 are excellent eating. Thus the Indians eat ducks in March, 

 and herons in September. We could not learn what becomes 

 of the gavanes during the swellings of the Orinoco, and why 

 they do not accompany the patos careteros in their migration 

 from the Orinoco to the Bio Branco. These regular mi- 

 grations of birds from one part of the tropics towards 

 another, in a zone which is during the whole year of the 

 same temperature, are very extraordinary phenomena. The 

 southern coasts of the West India Islands receive also every 

 year, at the period of the inundations of the great rivers of 

 Terra Firma, numerous flights of the fishing-birds of the 

 Orinoco, and of its tributary streams. We must presume 

 that the variations of drought and humidity in the equinoc- 

 tial zone have the same influence as the great changes of 

 temperature in our climates, on the habits of animals. The 

 heat of summer, and the pursuit of insects, call the hum- 

 ming-birds into the northern parts of the United States, and 

 into Canada as far as the parallels of Paris and Berlin : in 



* The swellings of the Nile take place much later than those of the 

 Orinoco; after the summer solstice, below Syene; and at Cairo in the 

 beginning of July. The Nile begins to sink near that city generally 

 about the 15th of October, and continues sinking till the 20th of May. 



