UR28M EIN noise (self-noise) level not in specs

I’m comparing audio interfaces for a field recording project where signal is verrrry low (animal very far away) but so is environmental noise, which means my success probably depends on the interface, and my mic, having lowest possible self-noise (e.g., thermal noise from resistors in preamps). I was surprised to not find this sort of information, like EIN in units of dBu, on the Steinberg website for their UR28M interface, which I own. Does anyone know this information for the UR28M? I’d be plugging into one of the Yamaha mic preamps and recording by USB. Thanks, John Thaden