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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. 2. June 2012 
TABLE 2. Timing of post-fledging events, estimated size of post-fledging range, and maximum distance from nest for 
Northern Pygmy-Owl family groups in the Rocky Mountains of Montana and Idaho. Blank spaces indicate insufficient data. 
Family group - 
Last female 
anendanee h 
Last male 
attendance 6 
Male return to 
nest stand’ 1 
Female return 
to nest stand' 1 
Initiation of 
natal dispersal 1 ’ 
Post-fledging 
range (nl 
Max diu 
lo nest 
MT-1 
12 
32 
39 
45 
42. 42 
91.8 ha (24) 
1.967 m 
MT-2 
22 
34 
45 
57 
35, 37 
92.5 ha (23) 
3.340 m 
MT-3 
19 
34 
50 
38 
40.2 ha (28) 
2.522 m 
MT-4 
10 
31 
37 
42 
34.6 ha (21) 
943 m 
ID-1 
30 
34 
Did not return 
e 
38.8 ha (23) 
1,200 m" 
ID-2 
9 
40 
ID-4 
48 
MT = Montana. ID = Idaho. 
Number of days after fledging. 
d Maximum distance that family groups were observed front nest sites, 
‘ Exact nest location unknown; location approximated on basis of first location that young were observed 
Male moved to new area at end of post-fledging period and did not return to nest stand during life of transmitter. 
in notebooks. We monitored five adults and two 
fledglings throughout the night for 1-3 nights 
each (10 nights total). We recorded owl locations 
every 2 hrs on those occasions. 
Data Analysis. —Date ranges (number of days 
after fledging) represent the earliest and latest dates 
on which specific events or behaviors were 
observed. The observation dates prior to and 
following an event were averaged to approximate 
the actual date il an event occurred between visits 
from an observer (mean lime between observation 
periods = 2.27 days, n = 78), Distances were 
measured in ArcMap 9.3.1 (ESRI 2008). We 
calculated the size of areas used by family groups 
between Hedging and initiation of natal dispersal 
(hereafter ‘post-fledging ranges’) in ArcMap 9.3.1 
with the Home Range Tools extension (100% 
Minimum Convex Polygon-Fixed Mean method: 
Rodgers et al. 2007). We use ‘males’ in reference 
to breeding males and ‘females’ in reference to 
breeding females. Gender of adults was classified 
on the basis ot behavior (vocalization and copula¬ 
tion) and presence/absence of brood patch. We did 
not classify gender of young due to the lack of non- 
invasive criteria for the species (Pyle 1997). 
RESULTS 
Movements and Family Group Association 
Fledging dates in Montana ranged from 28 June 
5 August (// = 11 ). Fledging dates in Idaho rani 
from 18 June to 1 July (n = 5). We direc 
observed young exiting the nest cavity at one ne 
* of seven ow|s 1,1 'ha* brood left the nest cav 
within a 6.5-hr period. The seventh owl did r 
leave the nest cavity until 23-29 hrs after the fir 
Brood size ranged from two to seven (median 
n — in). 
Young owls remained within —100 m of each 
other from the time of Hedging until the end of the 
dependency period, and were observed in groups 
with individuals spaced 0 to 30 m during 69% of 
observation periods (n = 91). Allopreening was 
observed between young during three observation 
periods, and between adults and young during 
four observation periods. 
Adult females attended young for 9 to 30 days 
after Hedging (Table 2). Females provisioned 
young with prey items that were delivered by 
males and prey they captured (54 and 46% of 
temule prey deliveries, respectively, n = 41). 
Males most often delivered prey to females and 
only rarely delivered prey directly to young 
during this period (88 and 12% of male prey 
deliveries observed during female attendance, 
respectively; n = 25). 
Females left their family groups 9 to 30 days 
after Hedging and were not observed associating 
with the young again. Family groups were 225 to 
1.178 m from nests when females terminated 
association with them. Females moved within 
their home ranges independently after departing 
family groups. Females used areas that did not 
overlap those used by the remaining family group 
members during this period with the exception of 
one female for a 3-day period. We did not 
observe this female associating with the remain¬ 
ing family group in that instance. We generally 
observed males within 200 m of family groups 
after females departed and prior to male depar¬ 
ture (84% of locations for which proximity was 
known, n = 37). Males continued to attend 
young until 31-34 days after fledging (Table 2). 
after which they were not observed associating 
with young again. 
