54 HOW BIRDS MIGRATE 



is based on the automatic and mechanical registration of the road 

 followed, continued to work, in spite of the chloroform, absolutely 

 like other mechanical functions the circulation of the blood, the 

 digestive organs, and respiration in some way, without the knowl- 

 edge of the animal." 



Watson's experiments were made with Sooty and Noddy Terns, 

 among which he passed the breeding season of 1907 on their nesting- 

 ground on Bird Key, Dry Tortugas. He first captured and marked six 

 Noddies, and had them released at distances varying from 19.5 to 65.8 

 miles from the Key. All returned within from one and three-quarters 

 to about three and a half hours after being released. 



July 8, two Noddies and two Booties were captured and marked 

 and sent to Havana (108 miles) where they were released early on the 

 morning of the llth; all returned to the Key on the 12th. 



None of these birds, however, were sent beyond the normal range 

 of their species and it may be claimed that they were simply traveling 

 over a route with which they were familiar. In any event, the journey 

 was made unassisted by any trend of migration or established migratory 

 movement which they had simply to join. When breeding, these birds 

 are closely confined to the vicinity of their homes. Watson found that 

 they rarely went further than 15 knots from Bird Key. Some of the 

 birds returned alone, evidently dependent only on themselves for 

 guidance. 



A third test, in which the surrounding conditions were ideal, was made 

 with three Noddies and two Sooties which were captured and marked 

 on June 13, and sent from Bird Key to Key West. Here they were 

 transferred to the hold of the steamship ' Denver' where they were 

 both watered and fed while en route. On June 16, the birds were 

 released about 12 miles east of Cape Hatteras, approximately 1,081 

 miles by water from Bird Key. Both the Sooties were found on their 

 respective nests on the morning of June 21, and one of the Noddies 

 was observed several days later. 



Neither the Noddy nor Sooty Tern range, as a rule, north of the 

 Florida Keys. There is small probability, therefore, that the individuals 

 released off Hatteras had ever been over the route before and, for the 

 same reason, they could not have availed themselves of the experience 

 or example of migratory individuals of their own species; nor, since the 

 birds were released at the height of the nesting season, was there any 

 marked southward movement of birds in the line of which they might 

 follow. 



Even had there been such a movement, it is not probable that it 

 would have taken the birds southwest to the Florida Keys and thence 

 west to the Tortugas. This marked change in direction, due to the 

 fact that the birds' maritime habits would force tham to take a course 

 over the water, removes the direction of the wind as a possible guiding 

 agency, while the birds' unfamiliarity with the coast-line makes it 

 improbable that sight was of service to them in finding their way. In 



