Unusual sperm morphology in two sedentary songbird species

These data describe the morphology of bird sperm cells. The primary species are white-breasted nuthatch (Sitta carolinensis) and wrentit (Chamaea fasciata), for which we provide data from light microscopy and scanning electron microscopy (SEM). We additionally provide SEM data for Eurasian and Azores bullfinches (Pyrrhula pyrrhula and P. murina). For reproducibility, we provide summarised data on ecological and life history traits. We use that data in phylogenetic analyses to understand the evolution of the unusual sperm shape that is the focus of the paper.