Scratching beyond the surface: the evolution and functional role of avian eggshell surfaces

Birds are the largest and most diverse group of tetrapods living today. Their evolutionary success is in part attributed to the rapid evolution and diversification of their eggshell structure, allowing them to breed in nearly all habitats including glaciers, lakes, swamps and deserts.

Specific eggshell surface features may have evolved to improve the viability of avian eggs under different breeding conditions by (i) preventing debris from entering pores and clogging them, (ii) moderating gas and water vapour diffusion through pores, (iii) contributing to eggshell colouration and UV protection, and (iv) preventing embryo infection by impeding bacterial movement.

Our research

As most studies on eggshell surface structures have focused on one or several species, the full extent of eggshell surface variation and their function among birds is poorly understood. The aim of this study is to describe the surface structures and general topography of ~450 species of bird, randomly selected across the avian tree to capture variation in eggshell surface traits, and test whether life-history traits or phylogeny determine eggshell topography.

Eggshell surface topography characterisation was completed using scanning electron microscopy, or non-destructive impressions of the eggshell surface for more precious specimens. Three-dimensional (3D) surface profiles of the eggshell surface were accomplished using optical profilometry to quantify and compare surface roughness and structural complexity across species.

Preliminary results revealed high interspecific variation in the topography of the eggshell surface, and are potentially linked to the incubation environment. Using a multidisciplinary approach, our future work will attempt to verify the function of different surface features identified in this study, and its relevance to specific incubation conditions.


Attard MRG, Bowen J, Corado R, Hall LS, Dorey RA, Portugal SJ (minor revisions, manuscript ID: rsif-2021-0488) Ecological drivers of eggshell wettability in birds. Journal of Royal Society Interface.

Attard MRG, Portugal SJ (Under consideration) Global diversity and adaptations of avian eggshell thickness. Ecology Letters.

Research Collaborators:

  • James Bowen (Open University, UK)
  • RenĂ© Corado and Linnea Hall (Western Foundation of Vertebrate Zoology, California)
  • Douglas Russell (Natural History Museum, UK)
  • Steve Portugal (Royal Holloway University of London and Natural History Museum UK)