THE NATURAL HISTORY SURVEY. I3 



many species of birds select this area as a route for their migra- 

 tions, when every condition is so favorable to their needs. 



Occasionally, however, our area has had changes of tempera- 

 ture or other weather conditions which have been very severe for 

 bird life at times. The destruction of the more delicate of our 

 smaller birds during the spring migration period by a sudden 

 dropping of the temperature, high northeasterly winds and cold 

 rain storms, sometimes occurs. This may account for the scar- 

 city of certain species some years when during the previous year 

 they may have been common. This destruction from natural 

 causes is well explained by the observations of Dr. Joseph L. 

 Hancock.* He says: "Usually at this time of year (May 20) 

 the small land birds have passed us on their northward migration, 

 but this spring (1888) the weather has been so unfavorable that 

 they have been much delayed, the Warblers, especially, and have 

 suffered great loss of life. 



"While it is usual to see many of these birds passing from 

 tree to tree in the city, this spring on May 12 they were observed 

 in great numbers scattered over the ground in open lots, and on 

 the larger prairies within the city. Many were likewise noticed 

 in the thronged thoroughfares in the business part of the town 

 where some were run down by passing vehicles, and others met 

 their death under the feet of pedestrians. They would permit 

 a close approach, but when almost stepped upon would make a 

 spasmodic effort to mount into the air, only to find themselves 

 dropping back to the ground again, helpless, weak, and benumbed 

 by the cold. This strange effect of the weather on the birds 

 extended over many miles of country and across Lake Michigan 

 to the east. The shores between Lake Forest, Evanston, and Chi- 

 cago were bestrewn with lifeless birds which had been washed 

 up by the waves." Dr. Hancock found that many species of 

 birds were profoundly affected by the weather, allowing approach 

 which would be next to impossible under ordinary conditions. 

 He says the warblers could easily have been taken in a small 

 hand net. 



The destruction of bird life through the changes of tempera- 

 ture is very great, and often accounts for the scarcity of certain 

 birds or the change of their route of migration during some years. 

 ' The effect of severe weather which destroyed countless hundreds 

 of bluebirds in 1895 is splendidly described by Mr. Otto Widmah, 



*Auk. Vol. V, 1888, 432-433. 



