No. 391.] OBSERVATIONS ON OWLS. 569 
resultant number by the total number of owls divided by the 
number of days. The second vertical column of Table II shows 
which of the two species of owls were present each day, by the 
abbreviations “acc.” and “ wils.” for Asto acciptrinus and A. 
wilsonianus respectively. In the third vertical column of both 
tables ‘Micr. penn.” stands for Microtus pennsylvanicus 
(meadow mouse); “ Micr. pinet., for M. pinetorum (pine 
mouse); ‘‘ Micr. undet.,’’ for species of Microtus which could 
not be determined owing to the poor state of preserva- 
tion of the remains; “Mus,” for Mus musculus (house 
mouse) ; ‘‘ Peromyscus,” for P. leucopus (white-footed mouse) ; 
“« Zapus,” for Z. hudsonius (jumping mouse); “ Blar. brev.,” 
for Blarina brevicauda ; and “ Blar. parva,” for B. parva. 
For each owl on the arbor vitæ tree the daily average of 
small mammals, in the different weeks, varied from 1.57 to 
2.16. The collection of pellets made on January 8 had been 
accumulating for an undetermined period antecedent to that 
date. It is interesting to note that in the especially cold and 
stormy month of February the amount of food obtained by the 
owls was up to the average. The contents of these pellets 
may be summarized: 2 birds, 1 Blarina, 2 Peromyscus leucopus, 
1 Mus musculus, 6 Microtus pinetorum, 319 M. pennsylvanicus, 
and 18 undetermined individuals of Microtus. 
For the owls on the Norway spruce the daily average of 
small mammals per owl was 1.2 one week, and only .57 another; 
for the week given in the second transverse column of this 
table it would be 2.42, provided two owls were present each 
day, which I have good reasons to suppose to be the case, 
though I did not see the two each day. I could not determine 
how long the pellets had been accumulating which are given in 
the first transverse column. To summarize the pellets of this 
table: 1 Cambarus, 5 birds, 2 Blarina parva, | Zapus hud- 
sonius, and 105 Microtus pennsylvanicus. On the Norway 
spruce the short-eared owl was the regular resident, the long- 
eared owl more irregular in occurrence; and it is probably due 
to the differences in the feeding habits of the former that the 
bones in the pellets were more badly broken than is the case 
with long-eared owls, and that the daily food average was smaller. 
