“…For example, they appear at day eight in zebra finches ( Taeniopygia guttata , Passeriformes) and pigeons (Columbiformes), at day ten in chickens ( Gallus gallus , Galliformes), Japanese quail ( Coturnix coturnix , Galliformes), and Peking ducks ( Anas platyrhynchos , Anseriformes), at day 12 in budgerigars ( Melopsittacus undulatus , Psittaciformes), and at day 13 in Laysan albatross ( Phoebastria immutabilis , Procellariiformes; Bride & Gomot, ; Jacob & Ziswiler, and bibliography cited therein; Fukui, ; Fukui, ; Rehorek et al, ). However, only the characterization of the developmental stages of some of these species (i.e., Gallus gallus , Hamburger & Hamilton, ; Coturnix coturnix , Ainsworth, Stanley, & Evans, ; Phoebastria immutabilis , Rehorek, Smith, & Beeching, ) are available in the bibliography, including our species under study ( Myiopsitta monachus , Carril & Tambussi, ), and it is on these species that we base our comparisons. We rely on that embryological stages are an appropriate tool for comparison between birds because they standardize homologous morphological events which are independent of incubation time and body size, so that changes in development trajectories when comparing species could indicate heterochronies (Starck, ).…”