SHORT COMMUNICATIONS 
831 
The Wilson Journal of Ornithology 123(4):831-835, 2011 
Evidence of Medullary Bone in Two Species of Thrushes 
Maria E. Squire , 14 Joe C. Brague , 1 Robert J. Smith , 1 and Jennifer C. Owen 2 3 
ABSTRACT—We used micro-computed tomogra¬ 
phy to examine if medullary bone was present in Wood 
Thrush (Hylocichla mustelina) and Veery (Catharus 
fuscestens). two species of Passeriformes. Wc scanned 
twnes from males and females collected during spring 
and fail migration, and the breeding season. Medullary 
bone was found in the humerus, radius-ulna, and 
tibiotanius-ftbula of a breeding female Wood Thrush 
and a breeding female Veery, both of which were 
ovulatory at necropsy. Two other breeding female 
Wood Thrush, both post-ovulatory at necropsy, did 
not have medullary bone. We did not observe medullary 
bone in females collected during spring or tall 
migration, nor in any males. Our findings support the 
presence of medullary bone in breeding female 
passerines, but future studies with larger, targeted 
sample sizes are needed to examine the phenology ot 
medullary bone formation and resorption, and to 
explore the extent of medullary bone's role in eggshell 
formation in passerines. Received 20 January 2011. 
Accepted 19 April 2011. 
Calcium is an essential micronutrient necessary 
for successful breeding in birds (Perrins 1996) 
with the majority (98%) of the dry mass of the 
eggshell being calcium hydroxyapatite, the pri¬ 
mary mineral component in bone (Reynolds et al. 
-004). Successful egg formation requires ade¬ 
quate dietary calcium, yet little is known about 
calcium intake, storage, and utilization in wild 
birds (Reynolds and Perrins 2011). Studies have 
provided evidence that calcium limitations in wild 
birds have adverse reproductive consequences 
'Reynolds and Perrins 2011: table 2.2) including 
increased eggshell defects, reduced egg size, and 
incomplete clutches. Evidence suggests females 
are dependent upon calcium-rich foods in the days 
leading up to production of an eggshell ( Reynolds 
and Perrins 2011) and generally do not store 
calcium long-term (Graveland and van Gijzen 
'994). However, the possibility of wild birds 
1 Department of Biology. The University of Scranton. 
Scranton. PA 18510, USA 
Department of Biological Sciences. University o 
Southern Mississippi, Hattiesburg. MS 39406, USA. 
Current address: Department of Fisheries and Wildlife, 
Michigan Slate University, East Lansing. Ml 48824. USA. 
4 Corresponding author; e-mail: squirem 2 @scranton.edu 
storing calcium for the short-term in bone, and in 
particular as medullary bone, remains unclear. 
Medullary bone occurs in long bones of some 
female birds (Kyes and Potter 1934, Zambonin- 
Zallone and Mueller 1969. Clunies et al. 1992), 
and its predominant role is as a labile calcium 
resource that can be used to produce calcified 
eggshells (Dacke et al. 1993). Medullary bone 
presence and use as a calcium reservoir for 
eggshell production is well documented in 
Galliformes. including Domestic Chickens (Gal- 
lus galtus) (Mueller et al. 1964, Zambonin- 
Zallone and Mueller 1969. Clunies et al. 1992), 
White-tailed Ptarmigan (Lagopus leucura ) (Lar- 
ison cl al. 2001), and Japanese Quail (Cotumix 
japonica) (van de Velde et al. 1985. Yamamoto 
and Nagai 1992). Female pigeons (Columbi- 
formes) are known to form medullary bone in 
preparation for egg-laying (Kyes and Potter 
1934). Many of these studies (Kyes and Potter 
1934. Zambonin-Zallone and Mueller 1969, van 
de Velde el al. 1985, Clunies et al. 1992, 
Yamamoto and Nagai 1992) used histologic 
techniques to provide direct evidence for the 
presence of medullary bone. 
The presence of medullary bone in other taxa 
is not well established and, in particular for 
passerines, the evidence of medullary bone is 
equivocal. Most studies in passerines have used 
indirect methods to assay for medullary bone. 
Evidence including the uptake ol radioactive 
calcium in skeletons of female egg-laying Zebra 
Finches (Taeniopygici guttata) (Reynolds 1997), 
and differences in total body calcium in post- 
laying versus pre-laying and laying female House 
Sparrows (Passer domestic"*) (Krementz and 
Ankney 1995) suggest the presence of medullary 
bone. Ankney and Scott (1980) reported heavier 
leg bones in female Brown-headed Cowbtrds 
(Molothms ater) about to start laying and laying 
versus those finishing laying, suggesting the 
presence of medullary bone. Researchers, using 
a similar technique, concluded that female Great 
Tits (Parus major) do not have medullary bone 
(Graveland and van Gijzen 1994). 
Direct evidence for medullary bone presence in 
