warbler. This species winters in the Tropics and reaches New 

 Orleans about April 5, when the average temperature is 65 F. By 

 traveling north much faster than the spring season progresses, this 

 warbler reaches its breeding grounds in Manitoba the latter part of 

 May, when the average temperature is only 47 F. They encounter 

 progressively colder weather over their entire route and cross a strip 

 of country in the 15 days from May 1 1 to 25 that spring temperatures 

 normally take 35 days to cross. This "catching up" with spring is 

 habitual in species that winter south of the United States as well as in 

 most northern species that winter in the Gulf States. There appears 

 to be only six exceptions to this rule: the Canada goose, the mallard, 

 the pintail, the common crow, the red-winged blackbird, and the 

 robin. 



The snow goose presents a striking example of a late but very rapid 

 spring migration. Most all of these geese winter in the great coastal 

 marshes of Louisiana, where every year over 400,000 spend the 

 winter and congregations of 50,000 or more may be seen grazing in 

 the "pastures" or flying overhead in flocks of various sizes. Their 

 breeding grounds are chiefly on Baffin and Southampton Islands in 

 the northern part of Hudson Bay where conditions of severe cold 

 prevail except for a few weeks each year. The birds are not 

 stimulated to migrate even though the season in their winter 

 quarters is advancing rapidly while their nesting grounds are still 

 covered with a heavy blanket of ice and snow. This suggests the 

 stimulus for spring departure is regulated by an internal 

 mechanism, such as development of the gonads. Accordingly, blue 

 geese remain in the coastal marshes until the last of March or the first 

 of April, when the local birds are already busily engaged in 

 reproduction. The flight northward is rapid, almost nonstop so far as 

 the United States is concerned; although the birds are sometimes 

 recorded in large numbers in the Mississippi Valley, eastern South 

 Dakota, and southeastern Manitoba, there are few records anywhere 

 along the route of the great flocks that winter in Louisiana. When the 

 birds arrive in the James Bay region, they apparently enjoy a 

 prolonged period of rest because they are not seen in the vicinity of 

 their breeding grounds until the first of June. During the first 2 

 weeks of that month, they pour onto the Arctic tundra by the 

 thousands, and each pair immediately sets about the business of 

 rearing a brood. 



The American robin has been mentioned as a slow migrant, and, as 

 a species, it takes 78 days to make the 3,000-mile trip from Iowa to 

 Alaska, a stretch of country that is crossed by advancing spring in 68 

 days. In this case, however, it does not necessarily mean that 

 individual robins are slow. The northward movement of the species 

 probably depends upon the continual advance of birds from the rear, 

 so that the first individuals arriving in a suitable locality are the ones 

 that nest in that area, while the northward movement of the species is 

 continued by those still to come. 



There is great variation in the speed of migration at different 



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