Why are passerine eggshells spotted? Using calcium supplementation as a tool to explore eggshell pigmentation

Brulez, Kaat (2013). Why are passerine eggshells spotted? Using calcium supplementation as a tool to explore eggshell pigmentation. University of Birmingham. Ph.D.

Preview

Brulez13PhD.pdf
PDF - Accepted Version
Download (4MB)

Abstract

The eggshells of many avian species are spotted in appearance but the functional significance of such maculation is poorly understood. Protoporphyrin, responsible for brownish-red colouring on eggshells, is postulated to reinforce the structural integrity of eggshells under conditions when dietary calcium (Ca) is scarce. Within the context of this hypothesis, this thesis documents the use of Ca supplementation of two common British passerine species, blue (Cyanistes caeruleus) and great tits (Parus major), to explore the relationships between eggshell Ca and protoporphyrin content and visible pigment spotting. It further assesses the diversity of avian eggshell coloration using museum eggshells of 73 British passerine species. Despite low soil Ca availability, females were not necessarily Ca-limited but Ca-supplements may still influence eggshell traits and breeding behaviour, possibly by providing females with more time to invest in other activities. The importance of quantifying eggshell pigment concentrations directly, rather than using a proxy, is highlighted. Finally, this thesis shows that passerine eggshell pigment concentrations are highly phylogenetically conserved, thereby encouraging future studies testing key hypotheses to compare eggshell pigmentation of closely related species. This phylogenetic association may be essential to explain the functional significance of eggshell coloration of avian species.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):