1 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 Sooties were captured and marked 
and sent to Havana (108 miles) where they were released early on the 
morning of the 11th; 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 
