Growth is fundamental live history trait in all organisms and closely related with individual fitness. In altricial birds growth is restricted to the short period between hatching and fledging and mostly depends on food availability and frequent feeding by the parents. Different studies of birds have already emphasized within and between species how variation in growth rates underlies ecological conditions such as food availability or sibling competition. One major goal of this study was to describe the growth of five body traits (body mass, tarsus, 3rd primary, bill, crest) of European Hoopoe (Upupa epops) nestlings and to investigate the impact of various factors on these traits. From beginning of May 2014 until end of July 2014 these five body traits were measured every four days from a total of 236 Hoopoe nestlings from 39 nests in the plain of the upper Rhône valley in the canton Valais, south-western Switzerland and subsequently the data was analysed by applying non-linear mixed models. Model selection determined number of siblings, hatching date and the rank of the nestlings within a brood as the factors with the strongest influence on the growth trajectories. In addition, no difference of growth variability between nestlings or between nests was found. Another goal of this study was to find suitable parameters for an accurate age determination of Hoopoe nestlings, whereby the body traits bill and 3rd primary appeared to be suitable. This is, to my knowledge, the first study that has investigated the growth of Hoopoe nestlings thoroughly and with the use of nonlinear mixed models. However, since the influence of weather and sex, which are likely to be additional prominent factors, was not investigated within the framework of this study, further studies should ascertain the impact of these factors.