. The Canadian field-naturalist. 230 The Canadian Field-Naturalist Vol. 92 0) LU cc LU > o o LU CC U- O DC LU CQ TOO -I 80 60 • 40 20 (53). 0-25 26-50 5 75 '76-100 101-1350 INTERVALS OF RECOVERY DISTANCE (KM) Figure 1. Frequency histogram illustrating the pattern of recovery distances of 158 Great Horned Owls banded as nestlings. Figures in parentheses are percentage of total recoveries within the interval. Results Dispersal To gain an overview of horned owl move- ments in the north, we first examined the general pattern of band recoveries. Of 158 recoveries of birds banded as nestlings, 84
. The Canadian field-naturalist. 230 The Canadian Field-Naturalist Vol. 92 0) LU cc LU > o o LU CC U- O DC LU CQ TOO -I 80 60 • 40 20 (53). 0-25 26-50 5 75 '76-100 101-1350 INTERVALS OF RECOVERY DISTANCE (KM) Figure 1. Frequency histogram illustrating the pattern of recovery distances of 158 Great Horned Owls banded as nestlings. Figures in parentheses are percentage of total recoveries within the interval. Results Dispersal To gain an overview of horned owl move- ments in the north, we first examined the general pattern of band recoveries. Of 158 recoveries of birds banded as nestlings, 84 (53%) occurred within 25 km of the banding site. A frequency histogram of recovery distances (Figure 1) exhibited a sharp decline after 25 km, with the remaining recoveries spread over intervals of up to 1305 km. We thus arbitrarily defined all movements ^ 25 km as "non-dispersal" and those > 25 km as "; The proportion of banded owls recovered at distances > 25 km was highest (P < ) within the block of years of population decline (64 vs. 28%). This difference in apparent dispersal (Table 2) was also significant when annual recoveries within the 3-yr decreasing block were segregated and tested individually against years of population increase. Dispersal distances within each block of years were subjected to a log-transformation to ap- proximate a normal distribution before testing the difference between their means. The mean distance at which dispersing owls were recovered was greater (P < ) within the decreasing-year block (443 km) than during increasing years (323 km). The patterns of dispersal were also different: recoveries during years of increasing population were mainly (90%) within 100 km of the banding site, but five of the seven birds that exceeded this distance had moved beyond 700 km. Recoveries during declining years, on the other hand, were more continuously distri- buted, with only 51% at less than 100 km (Table
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