Structure and Composition of the Eggshell of a Passerine Bird, Setophaga ruticilla (Linnaeus, 1758)

The mineral composition of eggshells is assumed to be a conserved phylogenetic feature. Avian eggshells are composed of calcite, whereas those of taxa within Chelonia are aragonitic. Yet, the eggshells of a passerine bird were reported to be made of aragonite. Here, we report a new study of the same bird eggshells using a combination of in situ microscopy and chemical techniques. A microstructural analysis finds a similar arrangement to other avian eggshells, despite their very thin and fragile nature. Fourier transform infrared spectrometry (FTIR) and electron backscatter diffraction (EBSD) results also confirm that the eggshells are entirely composed of calcite. Our findings demonstrate that passerine eggshells are not an exception and similar to other birds and reinforce the phylogenetic placement of this bird species.

Automated summary

The mineral composition of bird eggshells has been considered a conserved phylogenetic feature, but a recent study found an exception in passerine bird eggshells, which are composed of aragonite rather than calcite like those of other bird species. Using a combination of in situ microscopy and chemical techniques, the research confirmed the unique mineral composition of passerine bird eggshells and reinforced their phylogenetic placement with other avian species.