90 
THE CONDOR 
| VoL.VIII 
combining the same records into four centers or clusters of observers, north, south, 
east and west of the city, and selecting the earliest date for each species in each of 
the four groups, we find the range of variation reduced to a day or two. [See also 
Table III.] 
In this way it can readily be seen that every report, no matter how fragmentary, 
is of value. It may contain one or two observations not noted at any other of the 
neighboring stations, while its deficiencies are made up in their records. 
I do not propose to quote a host of dates and figures, which are uninteresting 
and hard to follow, but I trust I may have made clear to you the value of combined 
local records and also the probability that the correct statement of migration at 
any given point will not be the citation of a single date but by some such state- 
ment as follows: “Stragglers of a certain species were arriving at Philadelphia 
from April 23 to 27 and the bulk movement occurred on April 28 and 29.” 
Migration constantly invites us to theorize and generally we find that we are 
working with very slender chains of evidence. What we need in the future, it 
seems to me, is more detailed and accurate data; and the plan of organizing large 
corps of observers at several important centers, as above described, is suggested 
as a means toward that end. 
TABLE I. Showing average (4 years) date of arrival at four stations within ten miles of 
Philadelphia and three stations over twenty miles distant. 
Station 
A 
B 
C 
D 
E 
F 
G 
Distance from Philadelphia 6 mi. 
8 mi. 
10 mi. 
10 mi. 
21 mi. 
22 mi. 
33 mi. 
Chcctura pelagica 
Apr. 19 
Apr. 22 
Apr. 23 
Apr. 23 
Apr. iS 
Apr. 21 
Apr. 23 
Pi rang a erythromelas 
May 6 
May 9 
May 8 
May 6 
May 9 
May 9 
May 8 
Seiurus aurocapillus 
Apr. 30 
May 3 
May 2 
Apr. 28 
Apr. 29 
'Apr. 30 
May 4 
Hylocichla mustelina 
Apr. 27 
May 3 
Apr. 30 
Apr. 29 
May 1 
Apr. 30 
Apr.' 30 
Savor n is phcebe 
Mch. 14 
Mch. 20 
Mch. 27 
Mch. 18 
Mch. 24 
Mch. 20 
Mch. 27 
TABLE II. Showing how first arrival reports from stations about Philadelphia are massed 
on certain days. 
Chimney Swift ( Chcetura pelagica). 
1903 
1904 
I9°5 
April 12 
arrived at 
1 station 
April 15 arr. at 2 sta. 
April 13 arr. 
at 1 sta. 
17 
<< i i 
1 “ 
21 “ “ 1 “ 
18 “ 
“ 2 “ 
19 
a 1 < 
6 “ 
22 “ “ 2 “ 
20 “ 
“ 9 “ 
20 
i < < < 
6 “ 
23 “ “ 1 “ 
21 “ 
“ 16 “ 
21 
U ( ( 
2 “ 
24 “ “8 “ 
22 “ 
“ 2 “ 
22 
< < < < 
3 “ 
25 “ “16 “ 
23 “ 
“ 3 “ 
23 
3 “ 
Wood Thrush ( Hylocichla mustelina). 
24 “ 
“ 4 “ 
1903 
1904 
1905 
April 23 
arr. at 1 sta. 
April 22 arr. at 2 sta. 
April 23 arr. 
at 1 sta. 
30 
“ “ 6 ‘ 
26 “ “ 1 “ 
24 “ 
“ 2 “ 
May 1 
“ “ 1 ‘ 
28 “ “ 1 “ 
25 “ 
“ 2 “ 
2 
“ “ 6 ‘ 
29 “ “ 6 “ 
26 “ 
“ 1 “ 
3 
“ “ 2 “ 
30 “ “ 7 “ 
27 “ 
“ 1 “ 
4 
“ “ 2 “ 
May 1 “ “ 6 “ 
28 “ 
“ 5 “ 
5 
“ “ 4 “ 
29 “ 
“ 2 “ 
30 “ 
“ 9 “ 
May 1 1 ‘ 
“ 2 “ 
TABLE HI. Illustrating method of combining data from 12 local observers into several 
“centers.” 
Chcctura pelagica, 1902: April 19 (1 sta.), April 21 (1), April 22 (5), April 23 (1), April 24 (2), 
April 26 (1), April 27 (1). Grouping the stations in four sections, or 
“centers," and taking the earliest date for each section, we have: Section A, 
April 21; B, April 22; C, April 19; I), April 22. 
Toxostoma rufum , 1902: April 22 (2), April 23 (1), April 24 (4), April 25 (1), April 26 (2), April 
27 (1), May 1 (1). Grouping them we have: Sect. A, April 22; B, April 22; C, 
April 23; D, April 24. 
Philadelphia, Pa. 
