Beckett and Proudfoot • NORTHERN SAW-WHET OWL MIGRATION 
531 
Predicted adult : juvenile ratio 
0.01 -0.38 
0.39 - 0.63 
| 0.64- 0.82 
HI 0.S3 - 1.03 
iH 1.04-1.38 
; ■ 1.39-3.77 
Banding station 
with > 50 banding 
events 
FIG. 7A = predicted age distribution of migrating Northern Saw-whet Owls in eastern North America, 1999 2008, 
based on age ratios at 132 stations with >50 banding events. 7B = predicted age distribution of owls at 89 stations in 
irruption years. 7C = predicted age distribution of owls at 101 stations in non-irruption years. Interpolation uses inverse- 
distance weighting of adult: juvenile ratios at banding stations within a 3 radius around each predicted raster cell. Dashed 
lines represent interpolation boundary. 
analysis indicated that many owls are banded in 
high-latitude breeding regions and recaptured 
nearby in subsequent years. This suggests that 
some owls may consistently travel from historical 
breeding areas and maintain high migration route 
fidelity. For example, if a bird is repeatedly 
captured at the same site in Wisconsin in different 
years during migration, it is more likely to have 
bred repeatedly in the western Great Lakes Basin 
'ban in eastern Quebec. Thus, although Northern 
Saw-whet Owls may only rarely reoccupy the 
Sa roe breeding territory (Marks and Doremus 
2000), they may still remain regionally tailhful. 
Marks and Doremus (2000:302) noted “the 
best evidence for nomadism would be the capture 
of marked individuals at widely separated breed¬ 
ing sites in different years,” yet a decade later 
there is still limited banding effort during the 
breeding season, and insufficient data to fully 
understand the scale of nomadism in Northern 
Saw-whet Owls. We conclude, based on the level 
of migration route fidelity found in this study, this 
species has ordered movement during migration 
and is not moving haphazardly in search of food. 
Migration Direction.— Our results show a clear 
southbound movement pattern indicated by the 
directional distribution of Northern Saw-whet 
Owls banded and recaptured in the same migra¬ 
tion season (Fig. 5). Most studies assume a 
southward migration based on the accumulation 
of southbound movement via recapture reports in 
their study areas (Brinker et al. 1997, Erdman et 
