Testosterone and paternity loss. Back transformed means (± 95% credible intervals) of post-capture and GnRH-induced testosterone levels did not differ between males that lost or did not lose paternity, when sampled during mating. When sampled during the nestling provisioning phase males that lost paternity had lower baseline and GnRH-induced levels of testosterone than males that did not lose paternity (inset). Testosterone levels increased after the GnRH-challenge in all groups. Grey dots represent post-capture testosterone levels; black dots represent GnRH-induced testosterone levels.