It's still possible that the birds had a disease that was just not detectable after death.

这些鸟仍然有可能患有一种死后无法检测到的疾病。

Human DNA is not quite everywhere: it was not detectable in deep-ocean water, or on remote beaches closed to the public.

人类 DNA 并非无处不在：在深海或不对公众开放的偏远海滩上检测不到。