A monocular does most of what a binocular does at roughly half the size and weight — one barrel, one hand, and a jacket pocket to carry it in. It is the optic you take when you are not sure you will need one at all.
The range here comes from Hawke Sport Optics: the Endurance ED line in compact and full-size formats plus a marine version, alongside the Nature-Trek series. For two-eyed glassing see binoculars, for more magnification see spotting scopes, or browse Hawke Sport Optics.