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The Wilson Journal of Ornithology 123(2):411 —413, 2011 
Cavity-nesting by the Black-billed Magpie (Pica hudsonia) 
K. Richard Stauffer 1 and L. Scott Johnson 23 
ABSTRACT.—We describe the first known instance 
of Black-billed Magpies {Pica hudsonia) nesting in a 
fully enclosed, pre-formed cavity. Magpies built an 
undomed nest of sticks in a nest box designed for Wood 
Uucks (Aix spunsu) near Olds, Alberta. Canada, in 
-008, All nesting material was removed From the box 
after an apparently successful nesting attempt. Magpies 
built a new nest in the box and Hedged at least four 
young in 2009. These observations indicate that cavity 
nesting is a distinct, novel behavioral trait that can arise 
in this species, We describe several potential costs of 
cavity nesting in this species, which may explain in part 
why this trail hus not become established in any of the 
many studied magpie populations around the world. 
Received 23 August 2010. Accepted 21 November 2010. 
1 Stauffer-Henley Inc.. 5342 57 Avenue. Olds, AB T4H 
•13, Canada. 
: Biological Sciences. Towson University, Towson. MD 
21252, USA. 
'Corresponding author: e-mail:sjohnson@towson.edu 
Species in many avian families nest in pre-formed 
cavities in trees, rocks, or other substrates. Cavity 
nesting presumably evolved in lineages in which 
nesting outside of cavities is ancestral (e.g., 
Hirundinae; Winkler and Sheldon 199.3) when some 
individuals acted on a propensity lo construct at least 
part of the nest within a pre-existing enclosed space. 
Cavity nesting then spread in the population because 
it resulted in relatively high fitness and was also 
heritable, either genetically or culturally. 
Humans are rarely in a position to document the 
occurrence in nature of a distinctly novel, 
potentially adaptive behavior trait such as cavity 
nesting. We provide the first recorded case of 
Black-billed Magpies (Pica hudsonia) nesting in a 
fully enclosed, pre-formed cavity. 
BACKGROUND AND OBSERVATIONS 
Magpies of the genus Pica are permanent 
residents throughout much of the northern hemi- 
