1S04 *1 Chapman on the Origin of Bird Migration. Ij 



Their case seems to me to be closely parallel to that of the sea- 

 birds previously cited. It is probable that in both cases these 

 colonies owe their origin to the instinct which guides a bird to 

 return to the place of its birth. Those individuals which selected 

 the most favorable breeding ground would rear their young in safety 

 and the young returning would aid in forming a future colony. 

 On the other hand, the progeny of those birds which did not 

 select so safe a home would be less likely to survive. 



Of this wonderful 'homing instinct' which plays so important a 

 part in the migration of birds I have no explanation to offer. We 

 know, however, that it exists, not only in birds, but in many other 

 animals. It is this instinct, aided by the "heredity of habit,' which 

 guides a bird to its nesting ground. The Carrier Pigeon is taught 

 its lines of flight by gradually extending its journeys ; a species 

 learns its routes of migration by gradually extending its range. 



As for the desertion of the breeding grounds and consequent 

 fall migration, there seems to be no question that it is due mainly 

 to the failure of the food-supply. Nevertheless, many species of 

 birds migrate long before there is apparently any reason for their 

 doing so. Early in July the Snipes and Plovers begin to appear 

 from their nesting grounds in the north. The first of August 

 finds numbers of our land-birds crossing the Gulf of Mexico en 

 route to their southern homes. Now, it has been frequently asked, 

 if failure of the food-supply is the cause of the fall migration, why 

 do these birds leave their breeding grounds at so early a date? 

 In reply I would ask, why should they remain? The object for 

 which they came is accomplished, and unless they are offered 

 some special inducement to stay, why should they not return to 

 the regions in which — and I would emphasize this — many of 

 them pass two-thirds of the year? 



The sea-birds I have mentioned desert their barren homes as 

 soon as their young are on the wing. The Arctic-nesting Snipe 

 and Plover hasten from the north to more fruitful feeding grounds 

 further south. In fact, as soon as the cares of the nesting season 

 are over, the summer home seems to possess few attractions. 

 Some birds at once hurry back to their southern resorts, while 

 others wander at will around the country, pausing wherever food 

 is abundant, and do not retreat southward until they are actually 

 forced to do so. 



