Frye and Jageman • NORTHERN PYGMY-OWL POST-FLEDGING ECOLOGY 
205 
independence simultaneous with or only slightly 
before they begin to disperse from their natal 
territory. Similarly, young Flammulated Owls 
become independent of adults only slightly before 
initiating natal dispersal (independence at 25 to 
32 days after fledging, dispersal at 30 to 35 days 
after fledging; Linkhart and Reynolds 1987). 
Eurasian Pygmy Owl fledglings become indepen¬ 
dent from adults at 27-34 days (Marks et al. 1999), 
which coincides with the range of independence 
dates we observed for Northern Pygmy-Owls (31 — 
34 days; Table 2). Ferruginous Pygmy-Owls 
disperse from their natal territory 7-8 weeks after 
fledging, the young often traveling >1 km in the 
first day (Proudfoot and Johnson 2000). Similarly, 
our observations indicate abrupt initial dispersal 
movements, assuming that signal losses were not 
due to transmitter failure in our study (an 
assumption we believe to be justified on the basis 
of expected battery life). Young either made abrupt 
movements of 965 to 2.015 m upon apparent 
initiation of natal dispersal, or their transmitter 
signals were lost. 
Our observations of abrupt movements to new 
areas by five males immediately after the post- 
fledging dependency period indicate variability in 
movement patterns after males stop attending 
young. Radiotelemetry data collected in our study 
areas between February and November suggest 
large abrupt movements are uncommon for adults 
during most of the year, but can occur for males 
both before and after the nesting season (unpubl. 
data). We hypothesize that some males shift home 
ranges seasonally to facilitate breeding with more 
sedentary females. Differential seasonal move¬ 
ments have been documented for other species of 
owls. Female Boreal Owls (Aegolius funereus), 
for example, will often move nomadically post- 
breeding, whereas associated males remain in the 
breeding territory (Wallin and Andersson 1981, 
Solheim 1983. Korpimaki 1986. Ldfgren et al. 
1986, Hayward et al. 1993). 
Previous descriptions of diel activity patterns 
during the post-fledging period are lacking, but 
increased crepuscular activity of adult Northern 
Pygmy-Owls has been noted during acoustical 
surveys (Nobel 1990, Sateret al. 2006) and during 
nest observations (Holt and Norton 1986, Rashid 
1999). We observed increased vocal activity and 
movements (including foraging) during morning 
and evening hours. It is possible the nearly 
persistent diurnal activity of young during obser¬ 
vation periods was stimulated by the observer’s 
presence, but we do not believe that was the case. 
Calls of fledglings were heard from a distance as 
observers approached family groups on most 
occasions, indicating they were active before our 
arrival. Previous reports suggesting that Northern 
Pygmy-Owls arc exclusively diurnal and crepus¬ 
cular were based on a lack of observed nocturnal 
activity (Holman 1926, Holt and Norton 1986, 
Noble 1990), rather than observed nocturnal 
inactivity of radio-marked owls. Our observations 
of nocturnal inactivity are consistent with previ¬ 
ous reports suggesting Northern Pygmy-Owls are 
primarily or exclusively diurnal and crepuscular. 
Contexts of most vocalizations observed in our 
study u'ere consistent with those described by 
Holt and Peterson (2000) and Frye (2005). 
However, to our knowledge, the use of the two- 
note call has not been described previously. This 
vocalization appeared to function as a contact call 
preceding prey deliveries. 
We were unable to estimate post-fledging 
mortality rates because of the limited number of 
young with transmitters. We suspected mortality 
of one fledgling in each of three family groups 
(MT-1. MT-4, ID-3) on the basis of reduced brood 
counts, but fates of those owls were unconfirmed. 
Estimating rates and sources of mortality during 
the post-fledging period should he a priority for 
future Northern Pygmy-Owl investigations. 
The patterns in post-fledging movements, 
behaviors, and development we documented 
advance our understanding of the ecology of this 
poorly studied species. Results from our two study 
areas, separated by >325 km and characterized by 
different forest composition, were highly consis¬ 
tent. Our sample sizes were small, but the size of 
post-fledging ranges, maximum distances that 
family groups were observed from nests, and 
estimated durations of post-fledging dependence 
should aid managers in minimizing impacts on 
Northern Pygmy-Owls during this critical life 
history stage. 
ACKNOWLEDGMENTS 
We thank those who made this project possible, but 
whose long list of names is impractical to include. We 
especially thank volunteer field assistants T. L. Gray. S. M. 
Westberg. K. K. Rogers, E. E. Fairbank. and S. L. Hahn for 
long hours in helping to capture owls and collect data. 
Funding was provided by the Rocky Mountain Front 
Institute of Natural History. Conservation Research Foun¬ 
dation. Wilson Ornithological Society. Nnormss Wildlife 
Foundation. University of Idaho Kvale and Norbcre/ 
Meiners awards. Pa/ouse Audubon Society, Clearwater 
