How patterning is timed during embryonic development is a fundamental question in developmental biology. To understand this, I have compared the development of the wings of different sized avian species: quails, chicks and turkeys. I find that development is accelerated in the smaller quail compared to the larger chick, and this occurs during the first 12 hours of limb outgrowth. Using tissue grafting techniques and gene expression analyses I have implicated the extrinsic signal, retinoic acid, in setting developmental timing in avian wings, in relation to a fixed growth rate between species. However, retinoic acid does not appear to set species-specific growth during the time frame analysed in my study. My work elucidates the influence of extrinsic signals on intrinsic timing mechanisms in specifying cell fates in the wing, and has significant implications for how patterning is timed and scaled in different sized species during embryonic development.