1908.] , NATURAL SCIENCES OF PHILADELPHIA. 137 



After consideratin-j; many methods it seems that the best date to 

 select is that upon Wiiich the species had arrived at half of the stations, 

 leaving out of consideration entirely the last quarter of the stations 

 that recorded the species, in order to eliminate the probably erroneous 

 or misleading dates. 



Dropping the last quarter of the stations in the case of the Ovenbird, 

 we shall have left for consideration in the three years twenty-three, 

 twenty-four and twenty-six records respectively, i.e. : 



1905— April 25, 28, 29 (8), 30 (10), May 2, 3, 4. 



1906— April 28 (2), 29 (7), 30 (4), Mav 1 (5), 2 (3), 3 (3). 



1907— April 26 (2), 27, 28 (4), 29 (5), 30 (2), May 1 (5), 2 (2), 5 (4), 6. 



The dates by which the species had reached half these stations will 

 then be 1905 April 30, 1906 April 30, 1907 April 30. This is perhaps 

 a poor example as the Ovenbird is such a regular migrant. Indeed a 

 mere glance at the records will show that the bulk of arrivals occurred 

 in 1905 on April 29 and 30, in 1906 on the same days and in 1907 on 

 April 28 and 29, which represents almost the same thing.^ 



In other cases,. however, the massing of arrivals upon a few days is by 

 no means so evident, and some such method as the above is absolutely 

 necessary. For example: 

 Pipilo erythrophthalmus (Towhee). 

 1905— March 24, April 11 (2), 12 (2), 14 (3), 18, 19, 20, 21 (2), 22 (2), 



23(3),24, 25(3),26(2),29, 30. 

 1906— March 6, April 7, 12, 15 (3), 16, 17, 19 (4), 20, 21 (5), 22 (3), 23, 



24, 25 (2), 27 (2), 30 (2). May 8. 

 1907— March 23, 30 (2), April 3, 4, 6, 14, 16, 20, 24, 26 (5), 27 (3), 28, 

 May 1, 4, 5, 6. 



Rejecting the last quarter of the records in each year and selecting 

 the middle one of those remaining, as before, we get: 

 1905 April 19, 1906 April 19, and 1907 April 20. 



Hirundo erytlirogastra (Barn Swallow). 



1905— April 7, 20 (3), 21, 23 (3), 24, 25 (3), 27, 29, 30 (4), May 6, 7, 9. 

 1906— April 11, 12, 14, 17, 19, 21 (2), 22 (3), 25 (4), 26, 28 (2), 30, 



May 3, 6, 19. 

 1907— March 27, April 6, 20, 21, 22 (2), 24 (3), 26 (2), 27, 28 (3), 30, 



May 1, 2, 4, 5 (3), 8 (2), 10, 11, 12, 14. 



1905 April 23, 1906 April 22, 1907 April 26. 



Toxostoma rufum (Brown Thrasher). 



1905— April 9, 13, 14 (2), 16, 18 (2), 19 (2), 21 (2), 22 (6), 23 (3), 24 (4), 

 25(2),26,29, 30, May3. 



' While the migration of 1907 was ver_y late, so far as most of the April and all 

 the May migrants were concerned, a wave just at this time brought the Oven- 

 birds at their normal date. 



