19 



PHI! i IP3, " I <u'i/. 



I \lllv 



1 Vprll 



Examples of this great potential accuracy could be multiplied 

 indefinitely, but we will confine ourselves to some of the most 

 striking. Cooke's report of Bird Migration in the years 1884 anil 

 1885 bear out the w onderful uniformity of progression i»t the Oriole. 

 t 'ooke sn\ s K " Were the surface of the earth le\ el and the climate 

 absolutely uniform, birds would arrive at a given place on approxi- 

 mately thesamedaj eachyear In the records of the Biological 

 survey the best example of uniformity in arrival is that of the 

 Chimnej Swift at New Market, Va., as noted in George M, Neese, 

 The dates of each year from 1884 to \ooo are respectively, April 

 16, 16, 15, it'-. \0. 11,9, 15,21, 11. 15, ll. 12, 7. 16, 14, L6, L2, LI, 

 9, 12, 12, 10." 



Dixon* quotes the case of the Puffins which arrive at St, 

 Kilda very regularly on the first day of May. while the Bartailed 

 Godwits reach the south coast o( England so near a certain date 

 that the twelfth oi May is known as ' Godwit-day.' 



Think for a moment what this means; a start from a more or 



less changeless climate, where environmental stimuli can hardly 

 account for a in oi the accuracy we have pointed out, with a 



journey ^i two thousand miles or more, fraught with innumerable 

 variations in wind, precipitation, (ood supply, etc., and in the ease 

 oi these first instances, an arrival at Boston, estimating the total 

 journey to occupy about two months, with an average error oi 



onlv l) This is comparable to a train being thirteen ami one- 



half minutes late in a journey of one hundred miles at forty miles 

 per hour. Yet if vve take into consideration that the bird has no 

 watch to start on, we ought really to figure its possible error of 



spring arriv al as t ho per cent of its total sojourn in w inter quarters, 



plus the time of its northern journey, which total period must 



be reckoned to be nearly eight months. This gives us an error o( 

 onlv _. I'\ . With the ease of the Chimney Swift the actual average 

 error as Cooke remarks is onlv 2.2 days in the whole period of 

 twenty -three v ears. 



It is natural that a v erv exceptional season, sueh as tin 1 eold 

 Mav of 1907, tuav have a \ erv marked effect on bird arrivals. 



1 The Migrator) Movements of Birds in Relation to the Weather. Year-book of 



\ v . 1910 p 

 'Dixon, rhe Migration of Birds, 1807 p 134 



