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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123. No. 4. December 2011 
view?of 2 ,hp M H CrOCT J mageS (1 ° Mm resolution * anterior 
view) of the radius and ulna from Wood Thrush # 16 (left) 
hon Z ! 10 (righ,) dc P ict ' n 8 .he presence of medulla^ 
bone m both females, The medullary bone in Wood Thn.sT 
f ! 6 was present throughout the entire length of both the 
adius and ulna. The medullary bone in Veery # |() was 
present ,n the prox.mal half of the radius Z ulna bu 
absent in the remainder of both bones. 
Anknev 1995). It is likely that studies unable 
thTTp l t,r dl " lar> ' braK in P as se™«. such 
lhat of Pah] et al. 1 1997), did not collect fcmal 
during the relatively short interval durine whi 
medullaty bone was present. 
gen^v? b ‘T- aS “ l0bile calcium f^erve 
ovulahon IT "nn'^utcly prior to onset 
ceases (Daeke T™ 
medullary hone in two P f “ | 
conjunction with its absence in the two post¬ 
ovulatory females, breeding males, and migrating 
males and females supports the hypothesis lhat 
these species of passerines, and perhaps all 
species of passerines as well as other avian 
Orders, form medullary bone to use as a labile 
source of calcium during eggshell production 
(Mueller et al. 1964. Zambonin-Zallone and 
Mueller 1969, Ankney and Scott 1980, Clunk' 
et al. 1992, Krementz and Ankney 1995). 
We found medullary bone in the long bones of 
female Wood Thrush and Veery during a period 
when these females were forming eggshells. We 
did not observe medullary bone in post-ovulatory 
females, males, or in female birds collected during 
other, non-breeding phases of the avian annual 
cycle. Our study was unique in that it used micro- 
computed tomography to directly image medul¬ 
lary bone in these specimens. We hypothesise that 
absence of medullary bonc in passerine females in 
this and other studies (Ankney and Scott 1980, 
Pahl et al. 1997, Ecva et al. 2000) may be a 
consequence of when birds were collected during 
the breeding season. Studies that actively target a 
larger number of females throughout the breeding 
season, permitting a more in-depth examination of 
the timeline of medullary bone formation and 
resorption in passerines, are required to evaluate 
this assumption. Future studies are needed to 
explore the extent of the role medullary bone has 
in eggshell formation in passerine birds. 
ACKNOWLEDGMENTS 
Funding for this research was provided by The 
University of Scranton. Pennsylvania Department oi 
Conservation and Natural Resources Wild Resource 
Conservation Program, and a National Science Foundation 
MR1 grant # 0722751. Operations at the Johnson Bayoiund 
Fort Morgan Peninsula study sites were funded r; J 
National Science Foundation LTREB grant to F. R 
|IOB 0078189J. The donation of bones from • T n a 
chicken by Robert Elkin is greatly appreciated. We thanlT 
R. Moore for allowing us to collect specimens at Jsihnson 
Bayou and Fort Morgan Peninsula, and Anna Bwhkt’ tor 
permission to collect specimens in northeastern Pemsyha- 
nia. We thank our many field assistants along with the 
undergraduates from The University of Scranton who 
contributed to this work. 
LITERATURE CITED 
Ankney, C. D. and D. M. Scott. 1980. Change "J 
nutrient reserves and diet of breeding Brown-headed 
Cowbirds. Auk 97:684-696. 
Barrow, w. C., C.-C. Chen, R. B. Hamilton, k 
Ouchley, AND T. J. Spengler. 2000. Disruption »» 
