384 YEARBOOK OF THE DEPARTMENT OF AGRICULTURE, 



birds, these average weather conditions are interspersed with occa- 

 sional drops of temperature that reduce insect-eating birds to the 

 verge of starvation. The purple martin, being an early migrant, is 

 peculiarly liable to such accidents. A storm in late June, 1903, in 

 southern New Hampshire swept the air of the bird's insect prey for 

 so long that all the young birds starved in their nesting boxes and a 

 large proportion of the old birds perished. Conversely, birds go 

 south in fall until they reach a district where usually they can ob- 

 tain sufficient food throughout winter. But sometimes they do not 

 go far enough to be out of reach of an exceptional blizzard. The 

 coast of South Carolina was visited in February, 1899, by a heavy 

 snowstorm, with the severest cold known there in two hundred years. 

 Thousands of fox sparrows, snowbirds, and woodcock starved, and 

 probably nine-tenths of the bluebirds and pine warblers shared their 

 miserable fate. 



The soundness in general of the birds' instincts is vindicated by 

 the fact that all these catastrophes, appalling though they are, do not 

 permanently diminish the bird population. Provided bad weather 

 has not permanently reduced the food supply, the birds eventually 

 regain their former numbers. 



Take the striking case of the bluebird. The winter of 1894-95 

 killed off so many of the bluebirds east of the Mississippi River that 

 in the spring of 1895 not a bluebird warble was heard in many a 

 town where the year before there had been a full chorus. Since then 

 their numbers have gradually increased, until now, were it not for 

 persecution by the English sparrow, the ever-w r elcome bluebirds 

 would be as numerous as ever. 



BIRDS PREFER MIGRATING IN WARM WEATHER. 



It is well known that migration is retarded by severe cold weather 

 and is accelerated by unusually warm weather. The 10 years of 

 observations at Lanesboro the most accurate record that has ever 

 been made in the United States show about 50 per cent more arrivals 

 during the warmer than during the colder days. The number of 

 birds that migrate during periods of low temperature is, however, 

 surprisingly large, and it might be objected that many of the birds 

 recorded during cold days really came unnoticed during a previous 

 warm spell, but the chances are that the errors of omission would 

 count most heavily in the opposite direction, since shivering birds are 

 apt to sink into silence and seclusion, while on warm days both melody 

 and motion betray their presence. 



A rise in temperature is interpreted by the birds as a signal for 

 migrating. At the end of a cold snap that has halted the advance, 

 the birds do not wait until the mercury rises to normal, but start 

 north as soon as there is a marked change for the better. The Lanes- 



