4 T HB, AUDUBON, BU sie isle 
where there was a probability of its referring to a nesting bird. Also, the 
increase and decline in numbers of summer residents, such as the redstart, 
show no appreciable variation from strictly migrant birds. This would 
indicate that the number of birds among our summer resident species, 
actually nesting in our area, is very small in relation to the number that 
pass on north. 
Assuming that the beginning date of the “maximum” period in table 1 
corresponds to the “average arrival” date in “Birds of the Chicago Region,” 
my greatest variation in arrival dates is in the case of the myrtle warbler, 
which I show to be May 5 as contrasted with April 12 for the Chicago list. 
I have only six records of the myrtle warbler prior to April 12, and my 
later average date may be partially due to the fact that I spent compara- 
tively little time in the field previous to that date. It is most significant 
though that I saw 67 birds the week following April 12, but the first week 
in May I recorded 87, and the second week 123, which indicates the trend 
was still upward when I was making observations regularly. However, 
there is a very wide fluctuation in the numbers of this warbler and addi- 
tional earlier observations could change my averages materially. I saw 
only one from May 5 to May 11 in 1988. For the same period in 1944 I 
saw 30, and on May 9, 1987, I recorded 34. 
The Connecticut and mourning warblers, which, unlike the myrtle are 
seen in very small numbers, offer interesting comparisons with the Chicago 
list both as to arrival dates and relative abundance. It shows the “average 
arrival” of the Connecticut warbler to be May 15 and the mourning warbler, 
May 16. I recorded one of the former on May 5 in 1941, and one of the 
latter May 19, 1940, another May 20, 1938, and all others of both species 
on May 21 or later. Furthermore, about half of the mourning warblers 
were recorded after May 23. Although the total of the two species observed 
amounts to only 28, one or the other was recorded at least once each year 
during the ten-year period. These facts seem to indicate very definitely 
that the average date of these birds is May 21 or later. 
My figures on the relative abundance of these two warblers also varies 
from the Chicago list. It describes the Connecticut as “fairly common” 
and the mourning warbler as “uncommon,” but I have seen the former 
only 11 times and the latter 17 times. This reverse order of the numbers 
seen is not important as a few additional years’ observations could easily 
change this order. The significant fact is that out of nearly 4,000 warblers 
entered in my records, a species that was seen only 11 times and recorded 
only 6 out of 10 years is listed as “common.” 
I do not regard the “earliest” date as listed in table 1 as very important 
since the real increase in numbers in many cases does not start until a 
week or ten days later. As an illustration of this point, I show the “earliest” 
record for the yellow-throat to be April 30, 1942, and during the next six 
days I saw only three more, but by May 7 there was a definite upward 
trend with six on that date. 
I am well aware of the fact that there are many factors that influence 
any compilation of the type I have made. One of the most obvious of these 
