SHORT COMMUNICATIONS 
403 
successfully in both 2008 and 2009 in an area with 
relatively high rates of nest failure. Thus, Female 
A may have destroyed the eggs in an attempt to 
mate exclusively with this high-quality male. 
Cerulean Warblers are predominantly monoga¬ 
mous. but evidence of clustered territoriality or 
semi-coloniality (Oliamyk and Robertson 1996. 
Roth and Islam 2007) and occasional polygyny 
exists. We observed six males feeding nestlings at 
simultaneous nests (of 100 males banded and over 
250 nests monitored) from 2007 to 2010 in the 
Cumberland Mountains. It is possible that Female 
A was either a secondary mate of the banded 
male, or wanted to become his mate and 
committed egg destruction to improve her chances 
of breeding exclusively with him. Similar causes 
of egg destruction and infanticide in the highly 
polygnous societies of Great Reed Warblers and 
House Sparrows have been documented (Hannsen 
et al. 1997, Veiga 2004). 
Female A may also have attempted to decrease 
local competition for resources by destroying the 
eggs. Food availability may have been low and 
Female A was attempting to decrease competition 
for that limited resource. Nests also contain 
limited resources (e.g.. spider webbing), but none 
of the nest material was used after the egg 
destruction, so this is an unlikely explanation. 
We did observe Female A return to the nest after 
destroying the eggs and apparently consume yolk, 
but resource exploitation seems an unlikely 
explanation for the behavior because nutritional 
gain was probably exceeded by the costs of the 
behavior (e.g., risk of injury and energy expend¬ 
ed). Female A may also have destroyed the eggs 
to reduce the number of young Cerulean Warbler 
nestlings/fledglings near her nest because a 
reduction in density of young may attract fewer 
predators to the area (Gunnarson et al. 2006). 
Conspecific egg destruction by Cerulean War¬ 
blers may he adaptive, but it may also be 
pathological with no adaptive value. Female A 
possessed unusual characteristics including a 
slight breast band, some streaking on her belly, 
sides, and flanks, and behavior that mimicked 
male aggression (wing Hicks and using her teet to 
grip Female B). Few female Cerulean Warblers 
that we have observed display these traits (<1% 
of females display breast bands or behave in this 
manner; TJB, pers. obs.). Egg destruction has not 
been documented in Parulidae despite the family 
being well-studied, and this case may be an 
aberration. However, Cerulean Warblers may be 
unique as a semi-colonial parulid, and they have 
been studied much less than many other parulid 
species. No previous study has documented egg 
predators or alternative causes of nest failure. 
Thus, conspecific egg destruction may be more 
common than we currently acknowledge. 
ACKNOWLEDGMENTS 
This study was performed in conjunction with the 
Cerulean Warbler Forest Management Experiment, which 
is funded by the National Fish and Wildlife Foundation, 
U.S. Fish and Wildlife Service, Nature Conservancy, and 
the National Council for Air and Stream Improvement. We 
thank L. M. Sicffennan and two anonymous reviewers for 
helpful comments on this manuscript. 
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