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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123, No. 1, March 2011 
Our study design incorporated an audio lure to 
attract migrating owls into the nets. This increases 
the probability of captures (Whalen and Watts 
1999, Project Owlnet 2000). Longland and Price 
(1991), in a study ot Barred Owls (Strix varia) using 
a taped audio playback, ascertained that Barred Owl 
response diminished with increased light. The risk 
of predation during the full moon may have 
deterred owls from investigating the audio lure. 
This explains decreased capture rates during full 
moon. The anomaly of a total lunar eclipse in 2004 
caused an uncharacteristic increase in capture rate. 
Increased light may prompt increased predator 
vigilance. Our results indicate owls are less likely to 
be moving or respond to an acoustic lure, when it 
was bright or dark. The Northern Saw-whet Owl 
has ditficult trade-offs as they must assess risk and 
combine feeding with predator vigilance. Increased 
predator vigilance was shown with lower capture 
rates during (he full and new moons. The Northern 
Saw-whet Owl apparently waits for a low risk 
situation to continue on migration and feeding. 
Significant differences in capture rates during each 
lunar event suggest the full moon effectively 
interrupts typical migration patterns. 
There was a total lunar eclipse during the full 
moon in 2004 which was associated with a 
substantial increase in number of Northern Saw- 
whet Owls captured. This small natural experi¬ 
ment provides further evidence that migratory 
movements by Northern Saw-whet Owls are 
influenced by lunar illumination. 
Moonlight is an exogenous factor that effectively 
decreases nocturnal activity in a variety of prey 
species. A1 varez-Castaneda et al (2004) found that 
number of rodents in Barn Owl (Tyto alba ) pellets 
ecreased during the full moon. In our study, body 
mass (unpubl. data) was lowest in the third quarter, 
suggesting a period of decreased foraging may occur 
prior to that interval. Further study may provide 
more insight into Northern Saw-whet Owl foraging 
behaviors during migration. Studies incorporating 
use of telemetry may enhance our understanding of 
night patterns of this species. Combining data from 
multiple studies will be a valuable resource in 
understanding the overall influence of lunar condi- 
tions on nocturnal migratory owls. 
for their support of this project. We also appreciate the 
support and encouragement of researchers connected with 
Project Owlnet. We especially thank Dawn Konkoly, Dan 
Zmoda, Doug Burton, Steve Clay, and John Leiser. Two 
anonymous reviewers provided exceptional comments on 
this manuscript. 
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