NISM researchers shellebrate the unveiling of UV scattering by bird eggs

A multidisciplinary team of researchers from NISM have recently unveiled the physical origin of UV scattering by eggshells.

Eggshells are essential for the reproduction of birds since the optical properties of shells have an impact on biological functions such as heating and UV protection, recognition by parents or camouflage. Whereas ultraviolet reflection by some bird eggshells was described in the literature, its physical origin had remained poorly understood until now and a prestigious oral contribution by NISM members to the Faraday Discussions held online in July this year. The oral presentation came along the publication of a peer-reviewed research article in the related journal of the Royal Society of Chemistry.

"In this study, we identified a porous structure in eggshells of several breeds of hen, duck and quail using techniques such as electron microscopy and mercury intrusion porosimetry. This structure was found in the so-called "calcified shell" (i.e., within the shell, at a depth ranging from ca. 20 µm to ca. 240 µm). With optical modelling, we found that these pores were responsible for reflectance peaks measured in the near-UV range by spectrophotometry.", explained Dr Sébastien Mouchet who supervised the project.

This UV response was analysed in terms of the distinct visual sensation of hens and humans: eggshells appearing achromatic (i.e., white) for humans proved to be chromatic for hens. It is hence very likely that this UV signal could play a biological role for birds. The optical simulations of the UV response from the observed porous structure relied on Mie scattering theory. This theory is known for explaining the white visual appearance of clouds and showed that light backscattering from the pores is the origin of the UV response from the investigated eggshells. Due to the similarities between the pore size distributions observed for beige hen eggshells and other investigated poultry eggshells, the research team comprising members of Prof. Olivier Deparis and Prof. Bao-Lian Su's labs expect Mie backscattering to be the origin of the UV response from the eggshells of many other bird species.

Mathieu Ladouce, Tarek Barakat, Bao-Lian Su, Olivier Deparis, Sébastien R. Mouchet, “Scattering of ultraviolet light by avian eggshells”, Faraday Discussions, May 2020, doi: 10.1039/D0FD00034E.

Mathieu Ladouce, Researcher, LPS,NISM, UNamur
Tarek Barakat, Postdoctoral Researcher, CMI, NISM, UNamur
Bao-Lian Su, Full Professor, CMI, NISM, UNamur
Olivier Deparis, Professor, LPS, NISM, UNamur
Sébastien R. Mouchet, FNRS Postdoctoral Researcher and Hon. Lecturer, LPS, NISM, UNamur