SHORT COMMUNICATIONS 
379 
et al. 2007b). and invasive earthworms continue to 
spread ihroughout most of north temperate North 
America (Hendrix et al. 2008). It is not econom¬ 
ically or logistically feasible to remove earth¬ 
worms, and it is important to prevent invasions into 
the remaining undisturbed areas. My study pro¬ 
vides evidence that some Lumhricus -free forest 
patches may provide optimal habitat conditions for 
supporting exceptionally high breeding densities of 
Hermit Thrushes. Additional research is required to 
clarify the relative influence of Lumhricus inva¬ 
sions, habitat characteristics of nest sites and 
patches, and abundance of important nesting 
substrates (e.g., clubmosses), on patterns of Hermit 
Thrush abundance. Research is also needed to leant 
if invasive earthworms provide a food benefit to 
Hemiit Thrushes, and whether a benefit could 
outweigh any adverse effects of earthworms to 
forest floor habitat. Finally, investigation of Hermit 
Thrush density in relation to invasion patterns 
across regional spatial scales will clarify whether 
earthworms are a significant concern for conser¬ 
vation of this species. 
ACKNOW LEDG M ENTS 
Field research was funded by the American Museum of 
Natural History, Bell Museum of Natural History, Dayton 
W'ilkie Foundation, Explorer's Club. Minnesota Ornithol¬ 
ogists’ Union, and Wisconsin Society for Ornithology. 
SRL was supported by a University of Minnesota 
Graduate School Fellowship and a National Science 
Foundation IGERT grant: Risk Analysis for Introduced 
Species and Genotypes (NSP DGF.-0653827). I thank 
C. C. Hakseth. L. E. Lambert. J. C. Mulligan, M. W. 
Shairow, Tammy Johns. H. M. Sireby. S. M. Peterson. B. 
M. Breen, C.-M. Hung, and S. S. Loss for Held assistance. 
• also thank R. B. Blair, L. E. Frelich. D, E. Andersen, and 
P. V. Bolstad. for guidance. B. M. Breen. H. M. Streby. 
and K. S G. Sundar for comments that improved the 
manuscript, and the Cable Natural History Museum for 
housing and office support. Fieldwork was conducted with 
appropriate permits and approval by the University of 
Minnesota Institutional Animal Care and Use Committee 
(protocol 0904A63062 ). 
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