SHORT COMMUNICATIONS 
645 
April May 
FIG. 4. Progressively early departures of female Eastern Screech-Owls from nest box during three successful nestling 
periods, 1999-2010, Falmouth, Massachusetts. 
2000, 35 days in 2002, and 31 days in 2010. The 
different lengths may be dependent on availability 
of food, which influenced growth of the owlets, 
and on the number of nestlings which Hedge on 
successive days. The observed range is in 
agreement with those given in other reports of 
Eastern Screech-Owl nestling periods, e.g., 30- 
32 days (Sherman 1911). 31-35 days (Kelso 
1950). 30-32 days (Johnsgard 1988). and 24- 
32 days (Gchlhach 1994). The increasingly earlier 
departures of the females during the nestling 
period has been reported earlier (Allard 1937, 
Gehlbach 1994) and most likely were due to the 
increasing food demand of the nestlings and. 
presumably, the increased crowding in the nest 
box as the owlets grow. Neither of the adults 
stayed in the box during the day in the last 4 to 
6 days of the nestling period, except for brief 
periods when they tied mobbing by other birds 
and sought refuge in the box. 
The departure delays reported here are longer 
'han those for more southerly locations, such as 
Washington. D.C. (Allard 1937) or Texas (Gehl¬ 
bach 1994). The Texas data are for M. a. 
Imbroucki) whereas my study deals with M. a. 
naevius (Gehlbach 2003). Allard's observations 
"ere for an area close to the intergrade zone 
between M. a. naevius and the nominate subspecies 
M. a. asio (Gehlbach 2003). The observed 
behavioral differences among populations of the 
three studies may aid in distinguishing between 
subspecies, but differences in length of twilight at 
the different latitudes, orientation of nest boxes 
with respect to sunset azimuth, and different foliage 
canopy may also have a role. The lack of any 
significant difference between male and female 
departure times appears to be unique to this study. 
ACKNOWLEDGMENTS 
1 thank F. R. Gehlbach for helpful correspondence during 
the early years of this work. R. R. Eakin, A. B. Hennessey, 
Ivan Valiela. and D. W. Holt for comments on the 
manuscript, and C. E. Braun for caretul editing. 
LITERATURE CITED 
Allard, H. a. 1937. Activity of the Screech Owl. Auk 
54:300-303. 
BOSAKOWSKI. T. 1989. Observations on the evening 
departure and activity of wintering Short-eared Owls 
in New Jersey. Journal of Raptor Research 23:162- 
166. 
Cavanagh, P. M. and G. RrrcuiSON. 1987. Variation in 
the bounce and whinny songs of the Eastern Screech- 
Owl. Wilson Bulletin 99:620-627. 
Delaney, D. K., T. G. Grubb, and P. Beier. 1999. 
Activity patterns of nesting Mexican Spotted Owls. 
Condor 101:42—49. 
Gehlbach. F. R. 1994. The Eastern Screech Owl. Texas 
A&M University Press. College Station. USA. 
Gehlbach, F. R. 2003. Body size variation and evolution- 
