Ball et al. • NOCTURNAL PROVISIONING OF THRUSHES 
513 
advantage of a longer active period by delivering 
more energy. Perhaps chick growth or digestive 
capacity was maximized and additional resources 
would be wasted. Alternatively, parents may have 
been provisioning at some optimal working 
capacity given the time and food resources 
available to fuel their own effort (Drent and Daan 
1980. Ydenberg 1994). We found little evidence of 
chick starvation in either study area (JRB. unpubl. 
data) suggesting that parents were not having 
difficulty meeting their chick’s energy needs. An 
extended provisioning period may improve repro¬ 
ductive performance if this was not the case. 
We did not find improvements in reproductive 
performance but we cannot conclude that other 
fitness benefits were not realized by parents that 
provisioned during the night period. Night-fed 
nestlings may have been heavier or structurally 
larger than non-night fed nestlings, which could 
increase their probability of surviving post- 
fledging (Monros el al. 2002). A longer active 
period and lower hourly provisioning rale could 
allow night-provisioning parents more lime to 
forage for themselves, which could increase 
survival through improvements in body condition 
and reduced risk-taking behavior. A lower hourly 
provisioning rale also would allow time for 
alternate fitness-related activities such as territo¬ 
rial defense, predator vigilance, or social interac¬ 
tions. We suggest researchers recognize the 
potential that birds can extend their active period 
well beyond the dawn to dusk period when 
comparing hourly provisioning rates between 
regions at different latitudes. We also suggest 
researchers consider fitness-related opportunities 
other than nesting success that may be provided 
by a lower hourly provision rate. 
ACKNOWLEDGMENTS 
We gratefully acknowledge the many technicians who 
assisted on this project. We especially thunk Craig Machtans 
for support in developing our northern research program on 
boreal songbirds. Sampling followed the Canadian Council 
on Animal Care Guidelines and Policies with approval from 
'he Binscicnces Animal Policy and Welfare Committee at the 
Lmvcrsity of Alberta (permit # 476505) and by permission of 
fnuronmcnl and Natural Resources. Government of the 
Northwest Territories (permit #‘s 3044, 4953) and Alberta 
Sustainable Resource Development. Fish and Wildlife 
Division. Government of Alberta (permit # 15096). Financial 
and in-kind support was provided by Environment Canada. 
Polar Continental Shelf Project of Natural Resources Canada. 
Northern Scientific Training Program of the Department of 
Indian and Northern Affairs (D1AND), Canadian Circumpo- 
,ar Institute of the University of Alberta, Alberta Conserva¬ 
tion Association, Alberta Cooperative Conservation Research 
Unit. Integrated Landscape Management Chair at the 
University of Alberta. Samson Security Solutions, Canadian 
Foundation for Innovation. Alberta Sport. Recreation, Parks 
and Wildlife Foundation. Canadian Helicopters Ltd. of Fort 
Simpson. NT, and the Litdlii Kue First Nation. Additional 
funding to JRB was provided by the University of Alberta. 
Alberta Ingenuity Fund, and the Natural Sciences and 
Engineering Research Council of Canada. We thank C. C. 
St. Clair. C. E. Braun, and 2 anonymous reviewers for 
valuable comments that improved our manuscript. 
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