Eggshell is essential for the reproduction of birds. The optical properties of their shell may have an impact on biological functions such as camouflage. While ultraviolet reflection by bird eggshells has been described in the scientific literature, the physical origin of this phenomenon remains poorly understood. In this master's thesis, reflectance peaks were observed by spectrophotometric measurements of hen, duck and quail eggshells. In addition, electron microscopy imaging revealed the presence of pores within the so-called "calcified shell" part (ie between ~20 µm and ~240 µm deep from the outer surface). Spectral measurements of excitation and emission by fluorescence provided characterization of fluorophores included in the shell. In addition, preliminary theoretical predictions using the Mie diffusion theory and the rigorous coupled-wave analysis suggest that these porous structures are responsible for the optical response observed in the UV.