.>->(> Stone, m •,■ ram, ljuly 



\pnl .'< Building their nest . 



May L2. Brought out their young, 

 isim m.i\ is BtoM ou1 their brood. 

 L805. March is. Pair and begin building their nest, 



May 18. Bro't out their young brood, 

 L808. March 9, Bluebirds pair 

 isis v pril ;;. Building their nest, 



\pril 22, Bluebird lays eggs, 



M;i\ is \ oung Bluebirds, 

 1819 Mi\ . Bluebird brought out their first brood which are under 

 protection of the father whilst the hen is laying tor the 

 next t'.itniU . 

 1820. March 16. Building nest. 



Comparison ov Migration Data with Recent Records. 



The thought thai will naturally occur to anyone who Has road 

 the foregoing record is: I low do Bartram's dates of arrival compare 

 w it h t hose tW* a century later? 



1 have called at tout ion elsewhere to the difficulty of securing 

 results of \aluo by comparing individual migration records. 1 By 

 comparing dates oi first arri\ al w e may ha\ e in one instance a \ ery 

 oarl\ straggler and in another the beginning o( the main Bight, 

 records which are really not comparable at all. Furthermore 

 1 have shown that i ho average dates oi arrival tor a number o( 

 years will differ materially in the records o( equally good observers 



situated only a few miles apart, owing to the fact that the first 



migrants o( a given species maj he present tor some days in one 

 neighborhood before an\ are seen in a nearby locality. 



For this reason it seems to me that reliable results can only he 



obtained l>\ combining the reeorils of a number of observers clus- 

 tered around a given center and selecting as a date for comparison 

 the da\ upon which the species has reached a majority o( the 

 stations, dropping oil' a definite proportion of obviously late records 



under eaeh species. 



The Delaware Valley Ornithological Club has had For twelve 



years a eorps o( from 20 to 35 observers recording migration 



immediately about Philadelphia and the results o( their work is 

 published annually in 'Cassinia.' 



i tYiv load, n.u Sci, PhiU LOOS, p i.; i 





