SHORT COMMUNICATIONS 
823 
TABLE 1. 
Boreal and Black-capped 
chickadee foraging time in 21 distinct vertical 
and horizontal zone 
s corresponding 
to spatial foraging position 
in trees. 
Percent lime per /.one 
Vertical zones 
Black-capped Chickadee 
Basal Medial 
Terminal 
Vertical /ones 
Basal 
Medial 
Terminal 
1 
2 
3 
4 
5 
6 
7 
2.42 
1.77 
10.88 
2.51 
0.00 
2.79 
0.00 
0.74 
28.65 
6.51 
20.19 
0.00 
0.93 
0.00 
1.30 
7.63 
13.30 
0.00 
0.37 
0.00 
0.00 
1 
2 
3 
4 
5 
6 
7 
0.80 
5.50 
1.49 
0.00 
0.00 
0.00 
0.00 
16.44 
22.20 
12.97 
11.21 
0.27 
0.00 
0.00 
19.26 
6.67 
0.27 
1.60 
1.33 
0.00 
0.00 
why these species may have more overlap than 
predicted by chance: (1) Boreal and Black-capped 
chickadees use resources that are in sufficient 
abundance and each species can overlap spatially 
without competing, or (2) these two species are 
currently competing for food resources. Both s])ecies 
appear to have similar diets, foraging heavily 
(>50%) in winter for dormant caterpillars (hetero- 
campids), pupae, and insect eggs (Bent 1946, 
Haftom 1974. Oatman 1985. Smith 1991). Similar 
foraging strategies (Moreno 1990. Ficken el al. 
19%), and the general microhabitat used for foraging 
support Boreal and Black-capped chickadees ap¬ 
parent overlap in use of food resources in winter. 
Higher niche overlap was lound in our study than 
in that conducted on Boreal and Black-capped 
chickadee partitioning during summer (Vassallo and 
Rice 1982). This may indicate foraging behavior 
and extent of niche overlap varies seasonally. 
We conclude niche overlap between Boreal anti 
Black-capped chickadees its indicated by random 
models is likely high. However, the macroscale 
region within Black-capped Chickadee habitats 
where niche overlap occurs is small as indicated 
by: ( I ) Boreal Chickadees use of localized boreal 
TABLE 2. Observed versus expected mean niche 
overlap based on three null randomization algorithms 
which use Pianka's index. Lower and upper probabilities 
indicate the observed niche overlap is either less than or 
greater than expected by chance (in the null model), 
respectively. 
forest regions, and (2) foraging overlap with Black- 
capped Chickadees in only three conifer species. 
Boreal Chickadees used the dense medially-located 
foliage of conifer crowns significantly more than 
Black-capped Chickadees. This may indicate dif¬ 
ferential resource use. hut further research is needed. 
ACKNOWLEDGMENTS 
We thank Joseph Youngman. Will Lewis, and Skye Haas 
for field assistance, the NMU Department of Biology tor 
supplies and equipment, and Scott Hickman. Alan Rebertus, 
and Susan Fawcett for comments on the study design and 
manuscript. 
Model 
Mean niche overlap 
Probability 
Observed 
Expected 
Lower 
Upper 
RA2 
0.676 
0.617 
0.719 
0.281 
RA3 
0.676 
0.306 
0.978 
0.022 
RA4 
0.676 
0.379 
0.964 
0.036 
LITERATURE CITED 
AI.ATAI.O, R. V,. D. Eriksson. L. Gustafsson, and K. 
Larsson. 1987. Exploitation competition influences 
the use of foraging sites by tits: experimental evidence. 
Ecology 68:284-290. 
Bi-NT A C 1946. Life histories of North American jays, 
croWS, and titmice. U.S- National Museum Bulletin 
191. „ . , 
BiNr-ORD. L C. 2006. Birds of the Keweenaw Peninsula. 
Michigan. Miscellaneous Publication 195. Museum ol 
Zoology University of Michigan. Ann Arbor. USA. 
Cabin, R. L and R. J. MITCHELL. 2000. To Bonferroni or 
not to Bonferroni: when and how are the questions. 
Bulletin of the Ecological Society of North America 
81:246-248. 
Dhondt. A. A. 1989. Ecological and evolutionary effects of 
interspecific competition in tits. Wilson Bulletin 
101:198-216. 
Evers. D. C. 1991. Boreal Chickadee (Poecile hudsonicus). 
Pages 322-323 in The atlas of breeding birds of 
Michigan (R. Brewer. G. A. McPeek. and R. J. Adams). 
Michigan State University Press. East Lansing. USA. 
Ficken, M. S.. M. A. McLaren, and J. P. Mailman. 1996. 
Boreal Chickadee <Poecile hwbonicas). The birds of 
North America. Number 254. 
Foote. J. R.. D. J. Menniel. L. M. Ratcliffe. and S. M. 
