360 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 39 



In an hour the gull flew 10 miles and covered 40. In 5 hours of 

 effortless flying he could have traveled 200 miles, or in 10 hours, 

 400. If, for the gull, we substitute a land bird and increase the 

 velocity of the wind, we have a natural answer as to how and why 

 migrants, without becoming exhausted, cross the Gulf of Mexico 

 in a single night. They ride the overhead gales that pour spring 

 into the eastern half of the United States. 



This explanation was forced on the writer after a spring night 

 2 years ago. On that night he took an airliner off at New Orleans, 

 bound for Atlanta, in a fresh southerly wind that increased in veloc- 

 ity to 60 miles an hour and shifted to south-southwest at 3,000 feet. 

 Even with throttles pulled back to reduce his air speed, he arrived 

 at Mobile and Montgomery far ahead of time. Northeast of Mont- 

 gomery the warm air began to overrun cold air at the surface, as 

 scud clouds beneath him attested. At Atlanta he landed down 

 through these clouds into a cold, northeast wind, although the 

 southerly gales were still aloft. The next morning the woods around 

 his home just outside of Atlanta were literally alive with migrants, 

 noisily happy in spite of the cold rain that was falling. There was 

 a natural deduction to be made — the birds had ridden across the 

 Gu^.f and as far inland as they could before being forced too far aloft 

 by the warm air running up the slope of the cold. 



From this deduction it is only a step to the general hypothesis 

 that, whenever possible, migrating birds ride the wind. It is, per- 

 haps, the most natural explanation that can be given, not only for 

 their crossing the Gulf of Mexico on what is a veritable Gulf Stream 

 of the air, but also why they seem to follow rivers on valley winds — 

 why they use mountain ridges and seacoasts when a quartering wind 

 creates a surf that will give them both lift and direction — why the 

 golden plover can ride nonstop from Nova Scotia to South America 

 around the rim of the "Bermuda High" but cannot come back the 

 same way — why land birds caught in a "cold front," or strong wind- 

 shift, over water must perish because the battling winds will not 

 allow them either to retreat or advance — why migrants land and 

 wait for days with a change of weather, for a change of weather is a 

 result of a change of winds — and finally why the bird's arrival and 

 departure dates fluctuate just as the schedule of the winds fluctuates. 



Spring and the birds came earl}'^ in 1938. Was one the cause and 

 the other the effect? Wliy not say that both are effects of the same 

 cause — that the influx of tropical air came early in 1938? The 

 birds migrate and the wind migrates. While it is a tilted earth 

 moving in its orbit that is the actual performance, the effect to us is 

 that the sun also migrates. The solar equator comes north in our 



