Fig. 1

Positively selected genes identified among lineages of birds. The phylogenetic relationships of bird taxa follow previous studies [14,15,16,17,18,19,20,21,22,23,24,25] and the Tree of Life Web Project (http://tolweb.org/Passeriformes). The diel activity of taxonomic bird orders follows one previous study [1]. The diurnal bird orders that contain taxa with occasional nocturnal activity are shown in blue, bird orders that harbor regular nocturnal taxa are shown in black, and diurnal bird orders with no known nocturnal activity are shown in gray. Please see Additional file 1 for species used for each of the bird orders. Bold lines indicate branches subjected to positive selection analyses in this study. The letters (A-K) in parentheses indicate the branches on which PSGs were detected in this study. The PSGs found are shown along the branches. The three PSGs found along the ancestral bird branch in our recently published study [8] are also shown. Please see the text for details about the positively selected genes identified and their corresponding specific branches