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BULLETIN 185, U. S. DEPARTMENT OF AGRICULTURE. 



morning to appease its hunger. Thus there would be 36 consecutive 

 hours without food, whereas by night migration the same journey 

 can be performed with only a 12 hours' fast. 



Migrating birds do not fly at their fastest. Their migration speed 

 is usually from 30 to 40 miles an hour and rarely exceeds 50. Flights 

 of a few hours a night, alternating with rests of one or more days, 



Fig. 1. — Distribution and migration of the bobolink, reedbird, or ricebird (Dolichonyx oryzivorus). Of 

 late years the bobolink has been extending its range into newly irrigated districts of -western United 

 States (indicated on the map by small encircled areas). Here we can witness the process of a growth in 

 the length of a migration route. So far those individuals, which have added a thousand miles to the 

 route and range into western Nevada, return over the old route and show no tendency to shorten the 

 trip by a direct flight across New Mexico to the Gulf coast of Texas. (See p. 37.) 



make the spring advance very slow, averaging for all species not 

 more than 23 miles a day, but with great variations of daily rate 

 among the different species. The exact number of miles which a 

 particular bird makes during one day's journey has not yet been 

 determined, and can not be ascertained until the tagging or banding 

 of birds by means of metal rings is carried out on a far more extensive 

 scale than has yet been possible. If migration were a steady 



