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The Wilson Journal of Ornithology 123(1): 158—160, 2011 
Lunar Influence on the Fall Migration of Northern Saw-whet Owls 
Jackie Speicher , 1 - 2 Lisa Schreffler , 1 and Darryl Speicher 1 
ABSTRACT. Seasonal migration is an importai 
component in the life cycle of Northern Saw-whet Ow 
(Aegolius acadicus). We evaluated the influence of tf 
tour lunar events (new moon, first quarter moon, fu 
moon, and last quarter moon) on nocturnal activity c 
orthem Saw-whet Owls based on captures during fa 
migration, 2000-2008. We found deferences betlee 
he lunar events with decreased capture rates during th 
full moon and the new moon. These results sugge< 
unar phase influences migratory movements In, 
behaviors in this species. This may be attributed ti 
predator avoidance during periods of relative brightnes 
19 OaTfr'toTt 1 ' ****** '° ^ 2 °° 9 ' Acce P'« 
The amount of light at night should be 
important variable to nocturnal migrants C 
potentially important influence on timing 
flights is the lunar cycle, which is described 
its four predictable conditions (first quarter moc 
full moon, last quarter moon, and new moo 
yle et al. (1993) reported that decreased lur 
hght was correlated with an increased number 
epartures during fall migration by landbirt 
S f eCtS behaV1OT * either mcreasi 
foraging behavior or predator avoidance. Lead- 
Storm Petrels (Oceanodroma leucorhoa) decrea 
activity during times of increased moonlight wh, 
PA18326°US V r ReSearCh Cent£r ’ R °‘ B °* Cresc 
2 Corresponding author; 
e-mail: Poconoavian@hotmail.com 
gull (Larus spp.) predation rates are relatively 
high (Watanuki 1986). This behavior modification 
suggests that petrels assess the risk of predation. 
Tropical Nightjars and other caprimulgids also 
increase foraging activity during periods of lunar 
illumination (Brigham and Barclay 1992, Jetz et al. 
2003). Changes in feeding behavior in association 
with changes in moonlight have also been noted for 
small mammals which are prey species (Price etal. 
1984, Gannon and Willig 1997, Lang et al. 2006. 
Schmidt 2006). Foraging activity typically decreas¬ 
es with increased lunar light. 
The Northern Saw-whet Owl (Aegolius acadi¬ 
cus) is a short-distance migrant that breeds in 
coniferous or mixed deciduous forests of North 
America. The adults are approximately 15-21 cm 
long (wingspan: 43 cm). Their weight ranges from 
65 to 151 g with females averaging slightly larger 
than males (Cornell Laboratory of Ornithology 
2009). Northern Saw-whet Owls prey primarily 
on small rodents, including mice (Peromyscus 
spp.) and voles ( Microtus spp.). 
The Northern Saw-whet Owl is also the potential 
prey of larger owls. Competing biological needs 
likely mean that owls react to lunar events in the 
context of foraging, avoiding predation, and 
movement. The full moon would be predicted to 
increase vigilance for predators leading to a 
decrease in foraging effort. Light conditions may 
also prompt a temporary pause in migratory flights 
or extended stopovers. We assessed the influence ot 
the lunar condition on the capture rate of Northern 
