SHORT COMMUNICATIONS 
413 
magpies in contests for cavities as, in Europe, 
Common Kestrels (F. tinnunculus) frequently 
usurp magpie nests for their own nesting attempts 
(Prokop 2004: see also Becker 1987). 
In addition, both male and female magpies have 
elongated tail feathers that can grow to >30 cm in 
length. Tails could be prone to damage when 
entering and moving about in the confines of a 
cavity. Research in Spain suggests the extent to 
which a magpie's tail is damaged signals both age 
and individual quality and could affect social 
status and mating success (Blanco and de la 
Puente 2002). Magpies in Northern Ireland with 
unbroken and less abraded tails pair earlier and 
fledged more offspring than magpies with dam¬ 
aged tails; individuals with badly broken tails 
often remain unmated (Fitzpatrick and Price 
1997). 
The fate of a novel trait also depends on 
whether it can be inherited. Whether the propen¬ 
sity to nest in a certain location or to construct the 
nest in a certain manner is genetically or 
culturally transmitted to offspring in magpies is 
unknown. However, Trost (1999) noted that nest 
structure within populations varies substantially 
and suggested magpies may imprint on their natal 
nest structure. 
Our observations indicate that cavity nesting is 
a distinct variation in behavioral form that can 
arise in Black-billed Magpie populations. This 
trait appears to be extremely rare or non-existent 
m the many populations of magpies studied to 
date suggesting this form is maladaptive, perhaps 
for reasons discussed above. 
ACKNOWLEDGMENTS 
We thank Deborah Buitron, C. E. Braun, and an 
anonymous reviewer for comments on the manuscript, 
and Brian Schmidt of the U.S. Museum of Natural History 
and Ren6 Corado of the Western Foundation of Vertebrate 
Zoology for providing measurements of magpie specimens. 
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