title: Developmental stage affects eggshell-breaking strength in two ground-nesting birds: the partridge (Alectoris rufa) and the quail (Coturnix japonica).
abstract: We examined the relationship between embryo development and egg hardness in two ground nesting bird species, the red-legged partridge (Alectoris rufa; n = 165 eggs) and the quail (Coturnix japonica; n = 148 eggs). For both species, we observed a strong effect of developmental stage on egg hardness. Eggs near hatching were significantly weaker than unincubated eggs (partridge: 18 and 23 N, respectively, and the quail 7 and 10 N, respectively). We additionally explored the effect of incubation on egg hardness in a control sample of non-fertilised quail eggs (i.e., without embryo development). The control eggs maintained in the incubator for the full incubation time (17 days) were significantly harder (7-9 N) than eggs containing fully developed chicks (5-7 N). Thus, the incubation conditions of high temperature and humidity alone seem not to have a significant effect on egg hardness, and support the important effect of calcium uptake.
authors.affiliation: Departamento de Biodiversidad y Biología Evolutiva, Museo Nacional de Ciencias Naturales (CSIC-MEC), C/José Gutiérrez Abascal 2, Madrid, Spain. aurora@mncn.csic.es
authors.forename: Aurora M
authors.initials: AM
authors.lastname: Castilla
authors.forename: Anthony
authors.initials: A
authors.lastname: Herrel
authors.forename: Guillém
authors.initials: G
authors.lastname: Díaz
authors.forename: Amadeu
authors.initials: A
authors.lastname: Francesch
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D004528:Egg Shell / Q000502:physiology*; D046094:Galliformes / Q000502:physiology*; D009425:Nesting Behavior / Q000502:physiology*; D010063:Ovum / Q000254:growth & development*