overcrowding which would necessarily ensue should they remain is prevented by 

 the spring exodus northward. No such movement occurs toward the correspond- 

 ing southern latitudes. 



It is said the weather in the winter home has nothing to do with starting the 

 birds on the spring migration, except in the case of a few. such as some ducks and 

 geese, which press northward as fast as open water appears. There is no change 

 in the temperature to warn the hundred or more species of North American birds 

 that it is time to migrate northward. "It must be a force from within," says the 

 Bulletin, "a physiological change warning them of the approach of the breeding 

 season," which causes the flight. 



Most of the birds migrate at night, though some fly during the day. Their 

 flight begins after dark and stops before dawn, they cover more distance before 

 midnight than they do after, though they do not fly at their greatest speed, seldom 

 traveling more than forty miles an hour. The average for all species in the spring 

 is not more than twenty-three miles a day forward advance ; the advance is slow 

 because the birds zigzag so much in search of food. 



Some Ijirds make \ery rapid and lengthy flights: the pur])le martin, for in- 

 stance, lias made the trip from New Orleans to Winnipeg in twelve nights, an 

 average of one hundred and twenty miles a night. The fact that most birds 

 can fly several hundred miles without stopping is proven by their flying across 

 the Gulf of Mexico, from five to seven hundred miles. 



Among the long-distance fliers are some of our commonest birds. The scar- 

 let tanger goes from Canada to Peru, the bobolink from New England to Brazil : 

 the martins, swallows, nighthawks and some thrushes, also to South America. 

 The black-poll warblers nest in Alaska and winter in South America — a 5,000 

 mile flight. The nighthawk has probably the longest land bird migration, he flies 

 7,000 miles from Alaska to Argentina. 



These distances are beaten by the shore birds, nineteen species of which nest 

 north of the Arctic circle, they all winter in South America and six species go 

 to Patagonia, a migration trip of 8,000 miles. The most amazing of all migrants 

 is the golden plover, whicli makes a single flight of 2,400 miles, the longest known 

 flight of any bird. Coming down from the Arctic the golden plover makes his 

 great non-stop flight from Nova Scotia ; leaving the coast the birds by the thou- 

 sands fly due south across the ocean to South America without a stop, it is not 

 fcnown how long it takes the birds. The golden plover of the Pacific makes a 

 2,000 mile flight straight across the islandless Pacific from Alaska to Hawaii. 



"It seems incredible that the birds do not lose their way," says the Bulletin, 

 but the fact remains that they return each year to their old haunts or nests and 

 never seem to be exhausted after their long flights. 



The habits of the chimney swift form an interesting mystery in the migratory 

 habits of birds. For five months they absolutely disappear, as if they went to an- 

 other planet. The flock slowly drifts south, joining with others until on the coast 

 of the Gulf of Mexico they become an innumerable host. Then they are gone. 



537 



