36 



HOMING AND RELATED ACTIVITIES OP BIRDS. 



Table 2. 



been incorporated. This summary will deal (1) with the migration of the 

 birds; (2) with the food and feeding instincts; (3) nesting activities; (4) swim- 

 ming activities; (5) retention of nesting habits. 



MIGRATION. 



The time of the northern migration apparently is variable. Some statistics 

 have been made of the approximate time of arrival at Bird Key by the warden 

 of the Department of Agriculture and the Audubon 

 Societies. This warden, since Tortugas was set aside 

 as a game reserve, is present throughout the breeding 

 season. Through the kmdness of Dr. T. S. Palmer we 

 are able to give, in table 2, the data of the time of 

 arrival at Bird Key. It will be seen that the time of 

 arrival is variable. The birds appear upon the island 

 rather suddenly, noddies and sooties coming together 

 in large flocks. They come in usually from the south 

 and southwest. Their route is unknown. It is pre- 

 sumed, however, that the group leaves the Caribbean 



Sea and comes to the southern shore of Cuba, and then takes a northwesterly 

 route to Tortugas. 



The southern migration begins some time in the latter part of August and 

 early part of September. Dr. Palmer furnishes us the dates given in table 3. 



Again we see that the date for the southern migra- 

 tion is variable.* The birds apparently leave in 

 flocks in a southwesterly direction. It would be in- 

 teresting to know if the old birds leave first, deserting 

 the immature birds. This seems quite improbable in 

 view of the fact that the eggs are laid durhig about 

 4 to 5 weeks in May and early June. This means, of 

 course, that the young birds mature from about the 

 middle of August to the middle of September. The 

 birds laying first would be ready to leave first with 

 their young. Many anecdotes are told about this colony and others to the 

 effect that the young are left by the parents and that an "enormous pilot 

 bird" appears always in time to lead the young to their distant and unknown 

 winter goal. 



*The impulse to migrate does not concern us in the present paper. It seems worth mention- 

 ing, however, that neither temperature nor food conditions (?) vary much from August 20 to 

 September 20. Dr. Mayer furnished us the 

 accompanying table of temperatures (given 

 in degrees Fahrenheit) covering the period of 

 August 9 to September 27. It will be seen 

 that the average temperature is practically 

 constant during the entire period of migra- 

 tion. These records tend to support the 

 commonly accepted view that the stimulus 

 to migration is an intraorganic one. (See 

 Chapman, Birds of Eastern North America, 

 p. 56.) 



Table 3. 



