Evidence of Medullary Bone in Two Species of Thrashes

We used micro-computed tomography to examine if medullary bone was present in Wood Thrush (Hylocichla mustelina) and Veery (Catharus fuscescens), two species of Passeriformes. We scanned bones from males and females collected during spring and fall migration, and the breeding season. Medullary bone was found in the humérus, radius-ulna, and tibiotarsus-fibula 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 fall 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 of medullary bone formation and résorption, and to explore the extent of medullary bone's role in eggshell formation in passerines.