SHORT COMMUNICATIONS 
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0 O O (3 
(B) (D) (F) (H) 
FIG. 1. MicroCT images of a representative cross section of the humerus (10 pm resolution) from an (A) female and 
(B) male Wood Thrush collected during spring migration, a (C) female and (D) male Wood Thrush collected during the 
breeding season, a (E) female and (F) male Wood Thrush collected during fall migration, and a representative cross section 
of the tibia (18 pm resolution) from a (G) female and (H) male Domestic Chicken. These images depict the presence of 
medullary bone only in the breeding female Wood Thrush and in the female Domestic Chicken. 
•ound in the humerus, radius-ulna (Fig. 2), and 
libiotarsus-fibula in both Wood Thrush # 16 and 
Veery # 10. 
The breeding status of females was assigned 
based on the presence of ovum formation in the 
oviduct, brood patch, and/or a nest. Wood Thrush 
# 16 had a fully vascularized brood patch and the 
nest was also found with four eggs. There was no 
evidence of ov um formation in the oviduct. Veery 
# 10 had a fully pigmented egg in the uterus, and 
two ova were found with only the yolk present. 
The remaining two Wood Thrush females had no 
e vidence of ovum formation in the oviduct nor 
had fully vascularized brood patches, indicating 
they were not incubating eggs. 
DISCUSSION 
Evidence in the literature of medullary bone in 
Passerines has been equivocal, even in studies that 
have directly looked for its presence (Ankney and 
Scott 1980, Pahl et al. 1997, Eeva et al. 2000). 
Histological analysis of breeding female Great 
Tits revealed the presence of medullary bone in 
the tibiotarsus, although it appeared sparse in 
some bones (Eeva et al. 2000), Medullary bone 
was found in 80% of pre-laying (without evidence 
of postovulatory follicles) and 100% oi laying 
(either with oviducal egg or evidence of postovu¬ 
latory follicles) female Brown-headed Cowbirds 
examined (Ankney and Scott 1980). However, 
radiographs of bones from Tree Swallows (7a- 
chxcineta bicolor), Brown-headed Cowbirds, and 
Great Tits demonstrated no difference in leg bone 
density between pre-laying (collected 9-22 days 
prior to laying) and post-laying (collected 17— 
25 days after completion of clutch) females, 
which suggests an absence ot medullary bone 
(Pahl et al. 1997). A possible confounding factor 
across these studies, including ours, is when birds 
were collected relative to the phenology of 
breeding. For example, both females with medul¬ 
lary bone in our study were collected during 
ovulation, whereas two female Wood Thrush that 
did not have medullary bone were post-oviposi- 
tion. There is increasing support that calcium 
storage in medullary bone may occur only a few 
days prior to and disappear shortly after egg 
laying (Ankney and Scott 1980, Krementz and 
