Screw-shaped bird sperm swim faster -- but it comes at a cost

The research was part of the thesis of PhD student Hanna Nyborg Støstad, investigating the peculiar spiral shape of songbird sperm. Støstad compared sperm cells of 36 bird species, from house sparrows to tree swallows, and found that species whose sperm had a particularly distinct spiral or corkscrew shape also had sperm with high average swimming speed. However, those species also tended to have high rates of abnormal or damaged sperm.