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THE WILSON JOURNAL OF ORNITHOLOGY • Vol 124. No. 4. December 2012 
be one such strategy (Nores and Nores 1994. Jones 
et al. 2007). Several accounts document kleptopar- 
asites obtaining material from a single host nest 
repeatedly, suggesting the behavior is not entirely 
opportunistic but that kleptoparasites actively seek 
out material from host nests, at least once a suitable 
host nest has been found (Haverschmidt 1952. Lev¬ 
el al. 1997. VanderWerf 1998. Jones et al. 2007). 
That we observed nest material kleptoparasitism 
suggests its benefits outweighed the costs of 
potentially aggressive encounters with the host 
and possible transmission of nest parasites. Appro¬ 
priate nesting material seemed abundant near 
ground level at the study site, suggesting kleplo- 
parasitism was likely not driven by overall scarcity 
oi material in the environment. However, birds 
often build nests using highly stereotyped move¬ 
ments and may find only certain pieces of 
ostensibly suitable material useful for construction 
(Hansel1 2000). Thus, by taking high quality 
construction materials from hosts’ nests, klepto¬ 
parasites may reduce locomotive energy expendi¬ 
tures and search time, potentially increasing time 
available for nest guarding. The kleptoparasites we 
observed transported only a single piece of nest 
material each time, suggesting kleptoparasitism did 
not reduce predation risk at their own nest by 
reducing the number of visits. We noted that 
Red-faced Spinetails (8 ± 2 m. mean ± SE, ,, = 
10 encounters). Thick-billed Euphonias (12 ± 
1 m - n = 11), and Golden-faced Tyrannulets (10 
± 1 m. n = 19) at our study site spent much of 
their time in the midstory, the same stratum 
occupied by the two Red-faced Spinetail nests 
(9 m for both nests). This vertical overlap is 
consistent with the hypothesis that kleptopara¬ 
sites reduce predation risk associated with nest 
material gathering by stealing material from 
existing nests in a familiar forest stratum and 
avoiding gathering material from less familiar 
strata such as the ground (Jones et al. 2007). We 
also observed Red-faced Spinetails re-using 
material from the older nest. Given that nest 
material recycling carries a risk of transmission 
of nest parasites, our observations of nest 
material recycling suggest its benefits out¬ 
weighed its potential costs. Our observations of 
nest material kleptoparasitism and re-use were 
limited, and we encourage collection of addi¬ 
tional data that might refine the hypotheses 
presented here. 
Identifying the exact source of nest material is 
often challenging under field conditions, which 
makes the prevalence of nest material kleptopar- 
asitism in birds difficult to assess. This behavior 
may be further under-reported in the literature 
because nest material kleptoparasitism is seidom 
addressed as a major topic. Others have suggested 
that nest material kleptoparasitism might have 
important ecological roles such as shaping the 
breeding seasons of bird species (VanderWerf 
1998). We encourage ornithologists to document 
instances ol nest material kleptoparasitism iii the 
literature. Video camera studies at bird nests, 
especially in the nest building stage, would be 
useful for evaluating the prevalence of nest 
material kleptoparasitism within a geographic or 
phylogenetic comparative framework. 
ACKNOWLEDGMENTS 
Our observations were possible because ol funding 
Provided by the U.S, Fish and Wildlife Service, (he 
National Fish and Wildlife Foundation, and (he National 
Council lor Air and Stream Improvement for an unreluted 
project on Cerulean Warblers (Setop/uiga cerul«l). D. L. 
Singer was supported by a Director's Associaleship Award 
bom the Ohio Agricultural Research and Development 
C enter. We thank J. M. Correa for access to field sites and 
U. J. Colorado for logistical help. We thank F. G. Stiles for 
sharing observations of nest material kleptoparasitism in 
neotropical birds and two anonymous reviewers for helpful 
comments on this manuscript. 
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