'The Wilson Journal 
of Ornithology 
Published by the Wilson Ornithological Society 
VOL. 124, NO. 2 June 2012 PAGES 199-428 
The Wilson Journal of Ornithology 124(2): 199-207, 2012 
POST-FLEDGING ECOLOGY OF NORTHERN PYGMY-OWLS IN THE 
ROCKY MOUNTAINS 
GRAHAM G. FRYE 1 - 1 AND HARRY R. .IAGEMAN 2 
ABSTRACT.—We investigated the post-Hedging ecology of the Northern Pygmy-Owl ( Glaucidium gnoma) at two study 
areas in the Rocky Mountains of Montana and Idaho from 2002 to 2009. Wc observed 16 successful nesting attempts that 
fledged from two to seven young. Fledging dates ranged from I8 June to 5 August and all nests were vacated within a 2-day 
period. Post-fledging behavioral data were collected regularly from Hedging through initiation of natal dispersal from five 
radiomarked family groups and opportunistically from three additional family groups Post-Hedging movement data were 
collected from eight family groups and two males that were suspected of nesting. Adults attended broods for 9 to 30 days 
(females) and 31 to 34 days (males) postfledging, after which they were not observed associating with their young. Young 
remained within the natal territory fur I to 10 days following departure of adult males, after which they abruptly initiated 
natal dispersal. Areas used by family groups during the post fledging dependency period ranged from 34.6 to 94.5 ha. 
Family groups were active throughout the day, hut activity was notably more intense during crepuscular periods. Our 
earliest observations of young hunting occurred 9 days after Hedging and 47% of all fledgling hunting attempts observed 
(» - 75) were successful. Adults and fledglings used vocalizations in contexts consistent With previous descriptions with 
the exception of an undcscribcd two-note vocal i/at inn that appeared to function as a contact call preceding prey deliveries. 
Received 6 August 2011. Accepted 0 December 2011. 
The post-fledging period is a crucial stage in 
the life history of birds. Fledglings develop the 
skills necessary for foraging (Weathers and 
Sullivan 1989. Bustamante 1993), (light (Busta¬ 
mante and Hiraldo 1989. Bustamante 1993), and 
predator avoidance (Weathers and Sullivan 1989) 
during this period, as well as acquire the energy 
reserves necessary for migration or dispersal 
Rocky Mountain Front Institute of Natural History . 226 
6" Avenue NE. Choteau. MT 59422. USA. 
Department of Fish and Wildlife Sciences. University of 
Idaho. Moscow. ID 83843. USA. 
Current address: Department of Biological Sciences. 
Boise State University, Boise, ID 83725, USA. 
4 Corresponding author; e-mail: ggfrye@rmf-inh.org 
(Wood el al. 1998). Adults provide fledglings 
with food (e.g.. Buitron 1988. Ogden and Stutch- 
bury 1997) and protection from predators (e.g., 
Greig-Smith 1980. Sergio and Bogliani 2001), 
w'hile serving as models for adaptive behavior 
(Galef and Laland 2005). 
Relatively few forest-nesting bird species have 
been studied during the post-fledging period 
because of the difficulty of collecting data from 
mobile family groups in forested environments 
(Ogden and Stutchbury 1997. Tarwater and 
Brawn 2010). Most post-fledging investigations 
have focused on estimating mortality, which can 
be an important factor in recruitment anil is often 
high (Lack 1954). For example, the mortality rate 
of fledgling Burrowing Owls (Athene cunicu/aria) 
199 
