142 



ORNITHOLOGIST 



[Vol. 9-No. 12 



and scientific study of the subject is as yet 

 possible, and the present records are given 

 as being the best that can now be obtained, 

 and as furnishing some material for the 

 use of the future student. The records of 

 fifty eight species for the spring of 1883, 

 give an average speed of twenty-three 

 miles a day for an average distance of four 

 hundred and twenty miles. A slightly 

 smaller number of species for the spring 

 of 1884. give exactly the same average 

 speed over an average distance of eight 

 hundred and sixty-one miles. This coinci- 

 dence, notwithstanding the very different 

 meteorological conditions of the two 

 springs, make it probable that future re- 

 cords will not materially change this rate. 

 A study of last year's records led to the 

 statement that birds migrate more rapidly 

 in the northern portion of their route than 

 in the southern. As this was based on the 

 notes of only one year, it became a matter 

 of much interest to know whether this 

 would hold good as a general law, or 

 whether it had been the result of specially 

 favorable conditions in the latter part of 

 the season. Accordingly this year, twenty- 

 five species of well known birds were se- 

 lected, that had full records, and a careful 

 study reveals the fact that they bear out 

 last year's statement. The distance trav- 

 elled was divided as nearly as possible into 

 two equal portions, and the speed calcu- 

 lated for each. Some of the records do 

 not admit of division, others show an equal 

 speed throughout, while six of them show 

 an increase of seventy-seven per cent in 

 speed for the northern half, and three show 

 an increase of forty-seven per cent. It 

 will thus be seen that the record is strongly 

 in favor of the increase. We can arrive at 

 the same result by calculating the average 

 speed of these twenty-five species for the 

 different months. We get the following 

 results: the average speed for March is 

 nineteen miles : for April, twenty-three 

 miles, and for May twenty-six miles per 

 day. This year's record also bears out the 



statement that the later in the season a 

 bird migrates, the higher average speed it 

 will attain. This would naturally be sup 

 posed from the preceding statements. 



These calculations are average and give 

 us the rate that the bird would travel, pro- 

 vided it moved regularly each clay. But 

 we know that many pauses occur, that on 

 many days there is no advance, hence on 

 the days of movement, the sj^eed must be 

 much higher than that calculated. This is 

 clearly seen in the case of the Purple Mar- 

 tin (P. subis.) From 38 40 to 46° its aver- 

 age rate is but thirteen miles a day. But 

 we have good reason to believe that there 

 was a pause from April 3d to April 18th. 

 and another from April 18th to May 3d. 

 Taking out the first of these pauses, it 

 raises the rate from 38 4l) to 43 43 to thirty- 

 five miles a day, and not counting the sec- 

 ond pause, the rate for the rest of the dis- 

 tance is twenty-eight miles. 



We must also take into consideration 

 the fact that in all probability the same 

 bird seldom migrates for several nights in 

 succession, but after a flight of a night or 

 two stops to rest for several days. So that 

 the birds migrating one night are not the 

 same individuals that were moving the 

 night before. 



We have said that the average rate for 

 April is greater than that for March, and 

 is exceeded by that for May, but we cannot 

 say that the actual number of miles per- 

 formed in a night's journey is therefore 

 greater. It may be so, and probably is, 

 but the known facts would be sufficiently 

 explained if we remember that the later in 

 the season a species moves, the less hind- 

 rance it will meet from the elements, and 

 the less number of enforced pauses there 

 will be in its journey. During the month 

 of May there are few if any nights that 

 migration does not take place, while a bird 

 that migrates in March must expect for at 

 least one week out of the four, to be 

 stopped by storms. 



